580 Pflanzen (Botanik)
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To fire action-potential-like electrical signals, the vacuole membrane requires the two-pore channel TPC1, formerly called SV channel. The TPC1/SV channel functions as a depolarization-stimulated, non-selective cation channel that is inhibited by luminal Ca\(^{2+}\). In our search for species-dependent functional TPC1 channel variants with different luminal Ca\(^{2+}\) sensitivity, we found in total three acidic residues present in Ca\(^{2+}\) sensor sites 2 and 3 of the Ca\(^{2+}\)-sensitive AtTPC1 channel from Arabidopsis thaliana that were neutral in its Vicia faba ortholog and also in those of many other Fabaceae. When expressed in the Arabidopsis AtTPC1-loss-of-function background, wild-type VfTPC1 was hypersensitive to vacuole depolarization and only weakly sensitive to blocking luminal Ca\(^{2+}\). When AtTPC1 was mutated for these VfTPC1-homologous polymorphic residues, two neutral substitutions in Ca\(^{2+}\) sensor site 3 alone were already sufficient for the Arabidopsis At-VfTPC1 channel mutant to gain VfTPC1-like voltage and luminal Ca\(^{2+}\) sensitivity that together rendered vacuoles hyperexcitable. Thus, natural TPC1 channel variants exist in plant families which may fine-tune vacuole excitability and adapt it to environmental settings of the particular ecological niche.
Key message
Mobile laser scanning and geometrical analysis revealed relationships between tree geometry and seed dispersal mechanism, latitude of origin, as well as growth.
Abstract
The structure and dynamics of a forest are defined by the architecture and growth patterns of its individual trees. In turn, tree architecture and growth result from the interplay between the genetic building plans and environmental factors. We set out to investigate whether (1) latitudinal adaptations of the crown shape occur due to characteristic solar elevation angles at a species’ origin, (2) architectural differences in trees are related to seed dispersal strategies, and (3) tree architecture relates to tree growth performance. We used mobile laser scanning (MLS) to scan 473 trees and generated three-dimensional data of each tree. Tree architectural complexity was then characterized by fractal analysis using the box-dimension approach along with a topological measure of the top heaviness of a tree. The tree species studied originated from various latitudinal ranges, but were grown in the same environmental settings in the arboretum. We found that trees originating from higher latitudes had significantly less top-heavy geometries than those from lower latitudes. Therefore, to a certain degree, the crown shape of tree species seems to be determined by their original habitat. We also found that tree species with wind-dispersed seeds had a higher structural complexity than those with animal-dispersed seeds (p < 0.001). Furthermore, tree architectural complexity was positively related to the growth performance of the trees (p < 0.001). We conclude that the use of 3D data from MLS in combination with geometrical analysis, including fractal analysis, is a promising tool to investigate tree architecture.
Ecophysiological adaptations of the cuticular water permeability within the Solanaceae family
(2024)
The cuticle, a complex lipidic layer synthesized by epidermal cells, covers and protects primary organs of all land plants. Its main function is to avoid plant desiccation by limiting non-stomatal water loss. The cuticular properties vary widely among plant species. So far, most of the cuticle-related studies have focused on a limited number of species, and studies addressing phylogenetically related plant species are rare. Moreover, comparative studies among organs from the same plant species are still scarce.
Thus, this study focus on organ-specificities of the cuticle within and between plant species of the Solanaceae family. Twenty-seven plant species of ten genera, including cultivated and non- cultivated species, were investigated to identify potential cuticular similarities. Structural, chemical and functional traits of fully expanded leaves, inflated fruiting calyces, and ripe fruits were analyzed.
The surface morphology was investigated by scanning electron microscopy. Leaves were mainly amphistomatic and covered by an epicuticular wax film. The diversity and distribution of trichomes varied among species. Only the leaves of S. grandiflora were glabrous. Plant species of the Leptostemonum subgenus had numerous prickles and non-glandular stellate trichomes. Fruits were stomata-free, except for S. muricatum, and a wax film covered their surface. Last, lenticel- like structures and remaining scars of broken trichomes were found on the surface of some Solanum fruits.
Cuticular water permeability was used as indicators of the cuticular transpiration barrier efficiency. The water permeability differed among plant species, organs and fruit types with values ranging up to one hundred-fold. The minimum leaf conductance ranged from 0.35 × 10-5 m s-1 in S. grandiflora to 31.54 × 10-5 m s-1 in S. muricatum. Cuticular permeability of fruits ranged from 0.64 × 10-5 m s-1 in S. dulcamara (fleshy berry) to 34.98 × 10-5 m s-1 in N. tabacum (capsule). Generally, the cuticular water loss of dry fruits was about to 5-fold higher than that of fleshy fruits.
Interestingly, comparisons between cultivated and non-cultivated species showed that wild species have the most efficient cuticular transpiration barrier in leaves and fruits. The average permeability of leaves and fruits of wild plant species was up to three-fold lower in comparison to the cultivated ones. Moreover, ripe fruits of P. ixocarpa and P. peruviana showed two-times lower cuticular transpiration when enclosed by the inflated fruiting calyx.
The cuticular chemical composition was examined using gas chromatography. Very-long-chain aliphatic compounds primarily composed the cuticular waxes, being mostly dominated by n- alkanes (up to 80% of the total wax load). Primary alkanols, alkanoic acids, alkyl esters and branched iso- and anteiso-alkanes were also frequently found. Although in minor amounts, sterols, pentacyclic triterpenoids, phenylmethyl esters, coumaric acid esters, and tocopherols were identified in the cuticular waxes. Cuticular wax coverages highly varied in solanaceous (62- fold variation). The cuticular wax load of fruits ranged from 0.55 μg cm−2 (Nicandra physalodes) to 33.99 μg cm−2 (S. pennellii), whereas the wax amount of leaves varied from 0.90 μg cm−2 (N. physalodes) to 28.42 μg cm−2 (S. burchellii). Finally, the wax load of inflated fruiting calyces ranged from 0.56 μg cm−2 in P. peruviana to 2.00 μg cm−2 in N. physalodes.
For the first time, a comparative study on the efficiency of the cuticular transpiration barrier in different plant organs of closely related plant species was conducted. Altogether, the cuticular chemical variability found in solanaceous species highlight species-, and organ-specific wax biosynthesis. These chemical variabilities might relate to the waterproofing properties of the plant cuticle, thereby influencing leaf and fruit performances. Additionally, the high cuticular water permeabilities of cultivated plant species suggest a potential existence of a trade-off between fruit organoleptic properties and the efficiency of the cuticular transpiration barrier. Last, the high cuticular water loss of the solanaceous dry fruits might be a physiological adaptation favouring seed dispersion.
A novel method for detecting and delineating coppice trees in UAV images to monitor tree decline
(2022)
Monitoring tree decline in arid and semi-arid zones requires methods that can provide up-to-date and accurate information on the health status of the trees at single-tree and sample plot levels. Unmanned Aerial Vehicles (UAVs) are considered as cost-effective and efficient tools to study tree structure and health at small scale, on which detecting and delineating tree crowns is the first step to extracting varied subsequent information. However, one of the major challenges in broadleaved tree cover is still detecting and delineating tree crowns in images. The frequent dominance of coppice structure in degraded semi-arid vegetation exacerbates this problem. Here, we present a new method based on edge detection for delineating tree crowns based on the features of oak trees in semi-arid coppice structures. The decline severity in individual stands can be analyzed by extracting relevant information such as texture from the crown area. Although the method presented in this study is not fully automated, it returned high performances including an F-score = 0.91. Associating the texture indices calculated in the canopy area with the phenotypic decline index suggested higher correlations of the GLCM texture indices with tree decline at the tree level and hence a high potential to be used for subsequent remote-sensing-assisted tree decline studies.
Sphingolipid long-chain bases (LCBs) are the building blocks of the biosynthesis of sphingolipids. They
are defined as structural elements of the plant cell membrane and play an important role
determining the fate of the cells. Complex ceramides represent a substantial fraction of total
sphingolipids which form a major part of eukaryotic membranes. At the same time, LCBs are well
known signaling molecules of cellular processes in eukaryotes and are involved in signal transduction
pathways in plants. High levels of LCBS have been shown to be associated with the induction of
programmed cell death as well as pathogen-derived toxin-induced cell death. Indeed, several studies
confirmed the regulatory function of sphingobases in plant programmed cell death (PCD):
(i) Spontaneous PCD and altered cell death reaction caused by mutated related genes of sphingobase
metabolism. (ii) Cell death conditions increases levels of LCBs. (iii) PCD due to interfered sphingolipid
metabolism provoked by toxins produced from necrotrophic pathogens, such as Fumonisin B1 (FB1).
Therefore, to prevent cell death and control cell death reaction, the regulation of levels of free LCBs
can be crucial.
The results of the present study challenged the comprehension of sphingobases and sphingolipid
levels during PCD. We provided detailed analysis of sphingolipids levels that revealed correlations of
certain sphingolipid species with cell death. Moreover, the investigation of sphingolipid biosynthesis
allowed us to understand the flux after the accumulation of high LCB levels. However, further
analysis of degradation products or sphingolipid mutant lines, would be required to fully understand
how high levels of sphingobases are being treated by the plant.
Epidermal fragments enriched in guard cells (GCs) were isolated from the halophyte quinoa (Chenopodium quinoa Wild.) species, and the response at the proteome level was studied after salinity treatment of 300 mM NaCl for 3 weeks. In total, 2147 proteins were identified, of which 36% were differentially expressed in response to salinity stress in GCs. Up and downregulated proteins included signaling molecules, enzyme modulators, transcription factors and oxidoreductases. The most abundant proteins induced by salt treatment were desiccation-responsive protein 29B (50-fold), osmotin-like protein OSML13 (13-fold), polycystin-1, lipoxygenase, alpha-toxin, and triacylglycerol lipase (PLAT) domain-containing protein 3-like (eight-fold), and dehydrin early responsive to dehydration (ERD14) (eight-fold). Ten proteins related to the gene ontology term “response to ABA” were upregulated in quinoa GC; this included aspartic protease, phospholipase D and plastid-lipid-associated protein. Additionally, seven proteins in the sucrose–starch pathway were upregulated in the GC in response to salinity stress, and accumulation of tryptophan synthase and L-methionine synthase (enzymes involved in the amino acid biosynthesis) was observed. Exogenous application of sucrose and tryptophan, L-methionine resulted in reduction in stomatal aperture and conductance, which could be advantageous for plants under salt stress. Eight aspartic proteinase proteins were highly upregulated in GCs of quinoa, and exogenous application of pepstatin A (an inhibitor of aspartic proteinase) was accompanied by higher oxidative stress and extremely low stomatal aperture and conductance, suggesting a possible role of aspartic proteinase in mitigating oxidative stress induced by saline conditions.
Soil salinity is a major environmental constraint affecting crop growth and threatening global food security. Plants adapt to salinity by optimizing the performance of stomata. Stomata are formed by two guard cells (GCs) that are morphologically and functionally distinct from the other leaf cells. These microscopic sphincters inserted into the wax-covered epidermis of the shoot balance CO\(_2\) intake for photosynthetic carbon gain and concomitant water loss. In order to better understand the molecular mechanisms underlying stomatal function under saline conditions, we used proteomics approach to study isolated GCs from the salt-tolerant sugar beet species. Of the 2088 proteins identified in sugar beet GCs, 82 were differentially regulated by salt treatment. According to bioinformatics analysis (GO enrichment analysis and protein classification), these proteins were involved in lipid metabolism, cell wall modification, ATP biosynthesis, and signaling. Among the significant differentially abundant proteins, several proteins classified as “stress proteins” were upregulated, including non-specific lipid transfer protein, chaperone proteins, heat shock proteins, inorganic pyrophosphatase 2, responsible for energized vacuole membrane for ion transportation. Moreover, several antioxidant enzymes (peroxide, superoxidase dismutase) were highly upregulated. Furthermore, cell wall proteins detected in GCs provided some evidence that GC walls were more flexible in response to salt stress. Proteins such as L-ascorbate oxidase that were constitutively high under both control and high salinity conditions may contribute to the ability of sugar beet GCs to adapt to salinity by mitigating salinity-induced oxidative stress.
A first assessment of canopy cover loss in Germany's forests after the 2018–2020 drought years
(2022)
Central Europe was hit by several unusually strong periods of drought and heat between 2018 and 2020. These droughts affected forest ecosystems. Cascading effects with bark beetle infestations in spruce stands were fatal to vast forest areas in Germany. We present the first assessment of canopy cover loss in Germany for the period of January 2018–April 2021. Our approach makes use of dense Sentinel-2 and Landsat-8 time-series data. We computed the disturbance index (DI) from the tasseled cap components brightness, greenness, and wetness. Using quantiles, we generated monthly DI composites and calculated anomalies in a reference period (2017). From the resulting map, we calculated the canopy cover loss statistics for administrative entities. Our results show a canopy cover loss of 501,000 ha for Germany, with large regional differences. The losses were largest in central Germany and reached up to two-thirds of coniferous forest loss in some districts. Our map has high spatial (10 m) and temporal (monthly) resolution and can be updated at any time.
Intercomparison of satellite-derived vegetation phenology is scarce in remote locations because of the limited coverage area and low temporal resolution of field observations. By their reliable near-ground observations and high-frequency data collection, PhenoCams can be a robust tool for intercomparison of land surface phenology derived from satellites. This study aims to investigate the transition dates of black spruce (Picea mariana (Mill.) B.S.P.) phenology by comparing fortnightly the MODIS normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI) extracted using the Google Earth Engine (GEE) platform with the daily PhenoCam-based green chromatic coordinate (GCC) index. Data were collected from 2016 to 2019 by PhenoCams installed in six mature stands along a latitudinal gradient of the boreal forests of Quebec, Canada. All time series were fitted by double-logistic functions, and the estimated parameters were compared between NDVI, EVI, and GCC. The onset of GCC occurred in the second week of May, whereas the ending of GCC occurred in the last week of September. We demonstrated that GCC was more correlated with EVI (R\(^2\) from 0.66 to 0.85) than NDVI (R\(^2\) from 0.52 to 0.68). In addition, the onset and ending of phenology were shown to differ by 3.5 and 5.4 days between EVI and GCC, respectively. Larger differences were detected between NDVI and GCC, 17.05 and 26.89 days for the onset and ending, respectively. EVI showed better estimations of the phenological dates than NDVI. This better performance is explained by the higher spectral sensitivity of EVI for multiple canopy leaf layers due to the presence of an additional blue band and an optimized soil factor value. Our study demonstrates that the phenological observations derived from PhenoCam are comparable with the EVI index. We conclude that EVI is more suitable than NDVI to assess phenology in evergreen species of the northern boreal region, where PhenoCam data are not available. The EVI index could be used as a reliable proxy of GCC for monitoring evergreen species phenology in areas with reduced access, or where repeated data collection from remote areas are logistically difficult due to the extreme weather.
Farmland tree cultivation is considered an important option for enhancing wood production. In South India, the native leaf-deciduous tree species Melia dubia is popular for short-rotation plantations. Across a rainfall gradient from 420 to 2170 mm year\(^{–1}\), we studied 186 farmland woodlots between one and nine years in age. The objectives were to identify the main factors controlling aboveground biomass (AGB) and growth rates. A power-law growth model predicts an average stand-level AGB of 93.8 Mg ha\(^{–1}\) for nine-year-old woodlots. The resulting average annual AGB increment over the length of the rotation cycle is 10.4 Mg ha\(^{–1}\) year\(^{–1}\), which falls within the range reported for other tropical tree plantations. When expressing the parameters of the growth model as functions of management, climate and soil variables, it explains 65% of the variance in AGB. The results indicate that water availability is the main driver of the growth of M. dubia. Compared to the effects of water availability, the effects of soil nutrients are 26% to 60% smaller. We conclude that because of its high biomass accumulation rates in farm forestry, M. dubia is a promising candidate for short-rotation plantations in South India and beyond.
Freely available satellite data at Google Earth Engine (GEE) cloud platform enables vegetation phenology analysis across different scales very efficiently. We evaluated seasonal and annual phenology of the old-growth Hyrcanian forests (HF) of northern Iran covering an area of ca. 1.9 million ha, and also focused on 15 UNESCO World Heritage Sites. We extracted bi-weekly MODIS-NDVI between 2017 and 2020 in GEE, which was used to identify the range of NDVI between two temporal stages. Then, changes in phenology and growth were analyzed by Sentinel 2-derived Temporal Normalized Phenology Index. We modelled between seasonal phenology and growth by additionally considering elevation, surface temperature, and monthly precipitation. Results indicated considerable difference in onset of forests along the longitudinal gradient of the HF. Faster growth was observed in low- and uplands of the western zone, whereas it was lower in both the mid-elevations and the western outskirts. Longitudinal range was a major driver of vegetation growth, to which environmental factors also differently but significantly contributed (p < 0.0001) along the west-east gradient. Our study developed at GEE provides a benchmark to examine the effects of environmental parameters on the vegetation growth of HF, which cover mountainous areas with partly no or limited accessibility.
To reach their target site, systemic pesticides must enter the plant from a spray droplet applied in the field. The uptake of an active ingredient (AI) takes place via the barrier-forming cuticular membrane, which is the outermost layer of the plant, separating it from the surrounding environment. Formulations are usually used which, in addition to the AI, also contain stabilizers and adjuvants. Adjuvants can either have surface-active properties or they act directly as barrier-modifying agents. The latter are grouped in the class of accelerating adjuvants, whereby individual variants may also have surface-active properties. The uptake of a pesticide from a spray droplet depends essentially on its permeability through the cuticular barrier. Permeability defines a combined parameter, which is the product of AI mobility and AI solubility within the cuticle. In recent decades, several tools have been developed that allowed the determination of individual parameters of organic compound penetration across the cuticular membrane. Nevertheless, earlier studies showed that mainly cuticular waxes are the barrier-determining component of the cuticular membrane and additionally, it was shown that mainly the very-long-chain aliphatic compounds (VLCAs) are responsible for establishing an effective barrier. However, the barrier-determining role of the individual VLCAs, being classified according to their respective functional groups, is still unknown.
Therefore, the following objectives were pursued and achieved in this work: (1) A new ATR-FTIR-based approach was developed to measure the temperature-dependent real-time diffusion kinetics of organic models for active ingredients (AIs) in paraffin wax, exclusively consisting of very-long chain alkanes. (2) The developed ATR-FTIR approach was applied to determine the diffusion kinetics of self-accelerating adjuvants in cuticular model waxes of different VLCA composition. At the same time, wax-specific changes were recorded in the respective IR spectra, which provided information about the respective wax modification. (3) The ATR-FTIR method was used to characterize the diffusion kinetics, as well as to determine the wax-specific sorption capacities for an AI-modeling organic compound and water in cuticular model waxes after adjuvant treatment. Regarding the individual chemical compositions and structures, conclusions were drawn about the adjuvant-specific modes of action (MoA).
In the first chapter, the ATR-FTIR based approach to determine organic compound diffusion kinetics in paraffin wax was successfully established. The diffusion kinetics of the AI modelling organic compounds heptyl parabene (HPB) and 4-cyanophenol (CNP) were recorded, comprising different lipophilicities and molecular volumes typical for AIs used in pesticide formulations. Derived diffusion coefficients ranged within 10-15 m2 s-1, thus being thoroughly higher than those obtained from previous experiments using an approach solely investigating desorption kinetics in reconstituted cuticular waxes. An ln-linear dependence between the diffusion coefficients and the applied diffusion temperature was demonstrated for the first time in cuticular model wax, from which activation energies were derived. The determined activation energies were 66.2 ± 7.4 kJ mol-1 and 56.4 ± 9.8 kJ mol-1, being in the expected range of already well-founded activation energies required for organic compound diffusion across cuticular membranes, which again confirmed the significant contribution of waxes to the cuticular barrier. Deviations from the assumed Fickian diffusion were attributed to co-occurring water diffusion and apparatus-specific properties.
In the second and third chapter, mainly the diffusion kinetics of accelerating adjuvants in the cuticular model waxes candelilla wax and carnauba wax were investigated, and simultaneously recorded changes in the wax-specific portion of the IR spectrum were interpreted as indications of plasticization. For this purpose, the oil derivative methyl oleate, as well as the organophosphate ester TEHP and three non-ionic monodisperse alcohol ethoxylates (AEs) C12E2, C12E4 and C12E6 were selected. Strong dependence of diffusion on the respective principal components of the mainly aliphatic waxes was demonstrated. The diffusion kinetics of the investigated adjuvants were faster in the n-alkane dominated candelilla wax than in the alkyl ester dominated carnauba wax. Furthermore, the equilibrium absorptions, indicating equilibrium concentrations, were also higher in candelilla wax than in carnauba wax. It was concluded that alkyl ester dominated waxes feature higher resistance to diffusion of accelerating adjuvants than alkane dominated waxes with shorter average chain lengths due to their structural integrity. This was also found either concerning candelilla/policosanol (n-alcohol) or candelilla/rice bran wax (alkyl-esters) blends: with increasing alcohol concentration, the barrier function was decreased, whereas it was increased with increasing alkyl ester concentration. However, due to the high variability of the individual diffusion curves, only a trend could be assumed here, but significant differences were not shown. The variability itself was described in terms of fluctuating crystalline arrangements and partial phase separation of the respective wax mixtures, which had inevitable effects on the adjuvant diffusion. However, diffusion kinetics also strongly depended on the studied adjuvants. Significantly slower methyl oleate diffusion accompanied by a less pronounced reduction in orthorhombic crystallinity was found in carnauba wax than in candelilla wax, whereas TEHP diffusion was significantly less dependent on the respective wax structure and therefore induced considerable plasticization in both waxes. Of particular interest was the AE diffusion into both waxes. Differences in diffusion kinetics were also found here between candelilla blends and carnauba wax. However, these depended equally on the degree of ethoxylation of the respective AEs. The lipophilic C12E2 showed approximately Fickian diffusion kinetics in both waxes, accompanied by a drastic reduction in orthorhombic crystallinity, especially in candelilla wax, whereas the more hydrophilic C12E6 showed significantly retarded diffusion kinetics associated with a smaller effect on orthorhombic crystallinity. The individual diffusion kinetics of the investigated adjuvants sometimes showed drastic deviations from the Fickian diffusion model, indicating a self-accelerating effect. Hence, adjuvant diffusion kinetics were accompanied by a distinct initial lag phase, indicating a critical concentration in the wax necessary for effective penetration, leading to sigmoidal rather than to exponential diffusion kinetics.
The last chapter dealt with the adjuvant-affected diffusion of the AI modelling CNP in candelilla and carnauba wax. Using ATR-FTIR, diffusion kinetics were recorded after adjuvant treatment, all of which were fully explicable based on the Fickian model, with high diffusion coefficients ranging from 10-14 to 10-13 m2 s-1. It is obvious that the diffusion coefficients presented in this work consistently demonstrated plasticization induced accelerated CNP mobilities. Furthermore, CNP equilibrium concentrations were derived, from which partition- and permeability coefficients could be determined. Significant differences between diffusion coefficients (mobility) and partition coefficients (solubility) were found on the one hand depending on the respective waxes, and on the other hand depending on treatment with respective adjuvants. Mobility was higher in candelilla wax than in carnauba wax only after methyl oleate treatment. Treatment with TEHP and AEs resulted in higher CNP mobility in the more polar alkyl ester dominated carnauba wax. The partition coefficients, on the other hand, were significantly lower after methyl oleate treatment in both candelilla and carnauba wax as followed by TEHP or AE treatment. Models were designed for the CNP penetration mode considering the respective adjuvants in both investigated waxes. Co-penetrating water, which is the main ingredient of spray formulations applied in the field, was likely the reason for the drastic differences in adjuvant efficacy. Especially the investigated AEs favored an enormous water uptake in both waxes with increasing ethoxylation level. Surprisingly, this effect was also found for the lipophilic TEHP in both waxes. This led to the assumption that the AI permeability is not exclusively determined by adjuvant induced plasticization, but also depends on a “secondary plasticization”, induced by adjuvant-attracted co-penetrating water, consequently leading to swelling and drastic destabilization of the crystalline wax structure.
The successful establishment of the presented ATR-FTIR method represents a milestone for the study of adjuvant and AI diffusion kinetics in cuticular waxes. In particular, the simultaneously detectable wax modification and, moreover, the determinable water uptake form a perfect basis to establish the ATR-FTIR system as a universal screening tool for wax-adjuvants-AI-water interaction in crop protection science.
1. Pollination services of cacao are crucial for global chocolate production, yet remain critically understudied, particularly in regions of origin of the species. Notably, uncertainties remain concerning the identity of cacao pollinators, the influence of landscape (forest distance) and management (shade cover) on flower visitation and the role of pollen deposition in limiting fruit set.
2. Here, we aimed to improve understanding of cacao pollination by studying limiting factors of fruit set in Peru, part of the centre of origin of cacao. Flower visitors were sampled with sticky insect glue in 20 cacao agroforests in two biogeographically distinct regions of Peru, across gradients of shade cover and forest distance. Further, we assessed pollen quantities and compared fruit set between naturally and manually pollinated flowers.
3. The most abundant flower visitors were aphids, ants and thrips in the north and thrips, midges and parasitoid wasps in the south of Peru. We present some evidence of increasing visitation rates from medium to high shade (40%–95% canopy closure) in the dry north, and opposite patterns in the semi-humid south, during the wet season.
4. Natural pollination resulted in remarkably low fruit set rates (2%), and very low pollen deposition. After hand pollination, fruit set more than tripled (7%), but was still low.
5. The diversity and high relative abundances of herbivore flower visitors limit our ability to draw conclusions on the functional role of different flower visitors. The remarkably low fruit set of naturally and even hand pollinated flowers indicates that other unaddressed factors limit cacao fruit production. Such factors could be, amongst others, a lack of effective pollinators, genetic incompatibility or resource limitation. Revealing efficient pollinator species and other causes of low fruit set rates is therefore key to establish location-specific management strategies and develop high yielding native cacao agroforestry systems in regions of origin of cacao
Sphingolipid long-chain bases (LCBs) are building blocks for membrane-localized sphingolipids, and are involved in signal transduction pathways in plants. Elevated LCB levels are associated with the induction of programmed cell death and pathogen-derived toxin-induced cell death. Therefore, levels of free LCBs can determine survival of plant cells. To elucidate the contribution of metabolic pathways regulating high LCB levels, we applied the deuterium-labeled LCB D-erythro-sphinganine-d7 (D7-d18:0), the first LCB in sphingolipid biosynthesis, to Arabidopsis leaves and quantified labeled LCBs, LCB phosphates (LCB-Ps), and 14 abundant ceramide (Cer) species over time. We show that LCB D7-d18:0 is rapidly converted into the LCBs d18:0P, t18:0, and t18:0P. Deuterium-labeled ceramides were less abundant, but increased over time, with the highest levels detected for Cer(d18:0/16:0), Cer(d18:0/24:0), Cer(t18:0/16:0), and Cer(t18:0/22:0). A more than 50-fold increase of LCB-P levels after leaf incubation in LCB D7-d18:0 indicated that degradation of LCBs via LCB-Ps is important, and we hypothesized that LCB-P degradation could be a rate-limiting step to reduce high levels of LCBs. To functionally test this hypothesis, we constructed a transgenic line with dihydrosphingosine-1-phosphate lyase 1 (DPL1) under control of an inducible promotor. Higher expression of DPL1 significantly reduced elevated LCB-P and LCB levels induced by Fumonisin B1, and rendered plants more resistant against this fungal toxin. Taken together, we provide quantitative data on the contribution of major enzymatic pathways to reduce high LCB levels, which can trigger cell death. Specifically, we provide functional evidence that DPL1 can be a rate-limiting step in regulating high LCB levels.
Pivotal barrier properties of the hydrophobic plant cuticle covering aerial plant surfaces depend on its physicochemical composition. Among plant species and organs, compounds of this boundary layer between the plant interior and the environment vary considerably but cuticle-related studies comparing different organs from the same plant species are still scarce. Thus, this study focused on the cuticle profiles of Physalis peruviana, Physalis ixocarpa, Alkekengi officinarum, and Nicandra physalodes species. Inflated fruiting calyces enveloping fruits make Physalis, Alkekengi, and Nicandra highly recognizable genera among the Solanoideae subfamily. Although the inflation of fruiting calyces is well discussed in the literature still little is known about their post-floral functionalities. Cuticular composition, surface structure, and barrier function were examined and compared in fully expanded amphistomatous leaves, ripe astomatous fruits, and fully inflated hypostomatous fruiting calyces. Species- and organ-specific abundances of non-glandular and glandular trichomes revealed high structural diversity, covering not only abaxial and adaxial leaf surfaces but also fruiting calyx surfaces, whereas fruits were glabrous. Cuticular waxes, which limit non-stomatal transpiration, ranged from <1 μg cm\(^{−2}\) on P. peruviana fruiting calyces and N. physalodes fruits to 22 μg cm\(^{−2}\) on P. peruviana fruits. Very-long-chain aliphatic compounds, notably n-alkanes, iso-, and anteiso-branched alkanes, alkanols, alkanoic acids, and alkyl esters, dominated the cuticular wax coverages (≥86%). Diversity of cuticular wax patterns rose from leaves to fruiting calyces and peaked in fruits. The polymeric cutin matrix providing the structural framework for cuticular waxes was determined to range from 81 μg cm\(^{−2}\) for N. physalodes to 571 μg cm\(^{−2}\) for A. officinarum fruits. Cuticular transpiration barriers were highly efficient, with water permeabilities being ≤5 × 10\(^{−5}\) m s\(^{−1}\). Only the cuticular water permeability of N. physalodes fruits was 10 × 10\(^{−5}\) m s\(^{−1}\) leading to their early desiccation and fruits that easily split, whereas P. peruviana, P. ixocarpa, and A. officinarum bore fleshy fruits for extended periods after maturation. Regarding the functional significance, fruiting calyces establish a physicochemical shield that reduces water loss and enables fruit maturation within a protective microclimate, and promotes different seed dispersal strategies among plant species investigated.
Although a broad variety of classes of bioactive compounds have already been isolated from seaweeds of the genus Dictyota, most different species are still chemically and biologically unexplored. Dictyota species are well-known brown seaweeds belonging to the Dictyotaceae (Phaeophyta). The phytochemical composition within the genus Dictyota has recently received considerable interest, and a vast array of components, including diterpenes, sesquiterepenes, sterols, amino acids, as well as saturated and polyunsaturated fatty acids, have been characterized. The contribution of these valued metabolites to the biological potential, which includes anti-proliferative, anti-microbial, antiviral, antioxidant, anti-inflammatory, and anti-hyperpigmentation activities, of the genus Dictyota has also been explored. Therefore, this is the most comprehensive review, focusing on the published literature relevant to the chemically and pharmacologically diverse biopharmaceuticals isolated from different species of the genus Dictyota during the period from 1976 to now.
The plant hormone jasmonoyl-isoleucine (JA-Ile) is an important regulator of plant growth and defense in response to various biotic and abiotic stress cues. Under our experimental conditions, JA-Ile levels increased approximately seven-fold in NaCl-treated Arabidopsis thaliana roots. Although these levels were around 1000-fold lower than in wounded leaves, genes of the JA-Ile signaling pathway were induced by a factor of 100 or more. Induction was severely compromised in plants lacking the JA-Ile receptor CORONATINE INSENSITIVE 1 or enzymes required for JA-Ile biosynthesis. To explain efficient gene expression at very low JA-Ile levels, we hypothesized that salt-induced expression of the JA/JA-Ile transporter JAT1/AtABCG16 would lead to increased nuclear levels of JA-Ile. However, mutant plants with different jat1 alleles were similar to wild-type ones with respect to salt-induced gene expression. The mechanism that allows COI1-dependent gene expression at very low JA-Ile levels remains to be elucidated.
Plant transpiration is a key element in the hydrological cycle. Widely used methods for its assessment comprise sap flux techniques for whole-plant transpiration and porometry for leaf stomatal conductance. Recently emerging approaches based on surface temperatures and a wide range of machine learning techniques offer new possibilities to quantify transpiration. The focus of this study was to predict sap flux and leaf stomatal conductance based on drone-recorded and meteorological data and compare these predictions with in-situ measured transpiration. To build the prediction models, we applied classical statistical approaches and machine learning algorithms. The field work was conducted in an oil palm agroforest in lowland Sumatra. Random forest predictions yielded the highest congruence with measured sap flux (r\(^2\) = 0.87 for trees and r\(^2\) = 0.58 for palms) and confidence intervals for intercept and slope of a Passing-Bablok regression suggest interchangeability of the methods. Differences in model performance are indicated when predicting different tree species. Predictions for stomatal conductance were less congruent for all prediction methods, likely due to spatial and temporal offsets of the measurements. Overall, the applied drone and modelling scheme predicts whole-plant transpiration with high accuracy. We conclude that there is large potential in machine learning approaches for ecological applications such as predicting transpiration.
While much research has addressed the aboveground response of trees to climate warming and related water shortage, not much is known about the drought sensitivity of the fine root system, in particular of mature trees. This study investigates the response of topsoil (0–10 cm) fine root biomass (FRB), necromass (FRN), and fine root morphology of five temperate broadleaf tree species (Acer platanoides L., Carpinus betulus L., Fraxinus excelsior L., Quercus petraea (Matt.) Liebl., Tilia cordata Mill.) to a reduction in water availability, combining a precipitation gradient study (nine study sites; mean annual precipitation (MAP): 920–530 mm year\(^{−1}\)) with the comparison of a moist period (average spring conditions) and an exceptionally dry period in the summer of the subsequent year. The extent of the root necromass/biomass (N/B) ratio increase was used as a measure of the species’ belowground sensitivity to water deficits. We hypothesized that the N/B ratio increases with long-term (precipitation gradient) and short-term reductions (moist vs. dry period) of water availability, while FRB changes only a little. In four of the five species (exception: A. platanoides), FRB did not change with a reduction in MAP, whereas FRN and N/B ratio increased toward the dry sites under ample water supply (exception: Q. petraea). Q. petraea was also the only species not to reduce root tip frequency after summer drought. Different slopes of the N/B ratio-MAP relation similarly point at a lower belowground drought sensitivity of Q. petraea than of the other species. After summer drought, all species lost the MAP dependence of the N/B ratio. Thus, fine root mortality increased more at the moister than the drier sites, suggesting a generally lower belowground drought sensitivity of the drier stands. We conclude that the five species differ in their belowground drought response. Q. petraea follows the most conservative soil exploration strategy with a generally smaller FRB and more drought-tolerant fine roots, as it maintains relatively constant FRB, FRN, and morphology across spatial and temporal dimensions of soil water deficits.
Protein purification is the vital basis to study the function, structure and interaction of proteins. Widely used methods are affinity chromatography-based purifications, which require different chromatography columns and harsh conditions, such as acidic pH and/or adding imidazole or high salt concentration, to elute and collect the purified proteins. Here we established an easy and fast purification method for soluble proteins under mild conditions, based on the light-induced protein dimerization system improved light-induced dimer (iLID), which regulates protein binding and release with light. We utilize the biological membrane, which can be easily separated by centrifugation, as the port to anchor the target proteins. In Xenopus laevis oocyte and Escherichia coli, the blue light-sensitive part of iLID, AsLOV2-SsrA, was targeted to the plasma membrane by different membrane anchors. The other part of iLID, SspB, was fused with the protein of interest (POI) and expressed in the cytosol. The SspB-POI can be captured to the membrane fraction through light-induced binding to AsLOV2-SsrA and then released purely to fresh buffer in the dark after simple centrifugation and washing. This method, named mem-iLID, is very flexible in scale and economic. We demonstrate the quickly obtained yield of two pure and fully functional enzymes: a DNA polymerase and a light-activated adenylyl cyclase. Furthermore, we also designed a new SspB mutant for better dissociation and less interference with the POI, which could potentially facilitate other optogenetic manipulations of protein–protein interaction.