To avoid reaching lethal temperatures during periods of heat stress, plants may acclimate either their biochemical thermal tolerance, or leaf morphological and physiological characteristics to reduce leaf temperature (T leaf). While emerging evidence indicates that plants from warmer environments have a greater capacity to regulate T leaf, the extent of intraspecific variation and contribution of provenance is relatively unexplored. We tested whether upland and lowland provenances of four tropical tree species grown in a common garden differed in their thermal safety margins by measuring leaf thermal traits, midday leaf-to-air temperature differences (∆T leaf), and critical leaf temperature defined by chlorophyll fluorescence (T­ crit). Provenance variation was highly species- and trait- specific. Higher ∆T leaf and T­ crit were observed in the lowland provenance for Terminalia microcarpa, and in the upland provenance for Castanospermum australe, with no provenance differences observed in the other two species. Within-species covariation of T crit and ∆T leaf led to a convergence of thermal safety margins across provenances. These findings suggest that when grown under common conditions, lowland and upland provenances may not differ substantially in their vulnerability (defined here as thermal safety margin) to heat stress, despite differences in operating temperatures and T crit.

The massive leaf shedding in monoculture soybeans post-anthesis detrimentally impacts production, whereas relay strip intercropping can extend leaf area duration to enhance overall productivity. To reveal the reasons for leaf shedding in monoculture soybeans and how it affects the physiological and biochemical functions of source and sink organs, we conducted a four-year field experiment and a leaf-removal simulation experiment in relay strip intercropped soybeans to measure the phenotypic and physiological traits of leaves and nodules. The results showed that the strong self-shading of leaves in monoculture soybeans led to extensive defoliation, while the superior light environment in relay strip intercropped soybeans can promote the maintenance of a higher leaf area, nodule growth, and photosynthetic carbon allocation. With increasing leaf removal, leaf growth increased first and then decreased, and leaf defoliation gradually decreased. Extensive leaf-removal reduced Rubisco activity and sucrose phosphate synthase (SPS) activity in leaves, as well as the content of sucrose, malate, ATP, and energy charge (EC) in nodules, with a trade-off between leaf mass enhancement and weakened nodule growth. Notably, moderate leaf-removal could balance compensation and consumption. The total non-structural carbohydrates (TNC) in roots, N and Ureide in leaves and pods increased in unison, achieving the synergies between leaves and nodules to maintain a higher energy status and growth rate. Our study highlights that the favorable light environment in relay strip intercropping system shapes the coordinated functioning of above-ground and below-ground source-sink organs and effectively promoting photosynthesis and nitrogen fixation. These findings contribute to a better understanding of the underlying mechanisms of effective resource utilization in different cropping patterns, aiding in the sustainable development of food production.

A key challenge in molecular breeding is breaking trait coupling. Recently, Zhang et al. found inhibiting tissue-specific BR pathway expression in rice increases panicle number by over 40% without affecting grain size, offering a strategy to avoid hormonal negative effects by optimizing hormone spatial distribution.

Endoplasmic Reticulum-Plasma Membrane contact sites (ER-PM CS) are evolutionarily conserved membrane domains found in all eukaryotes, where the endoplasmic reticulum (ER) closely interfaces with the plasma membrane (PM). This short distance is achieved in plants through the action of tether proteins such as Synaptotagmins (SYTs). Arabidopsis comprises five SYT members ( SYT1-SYT5), but whether they possess overlapping or distinct biological functions remains elusive. SYT1, the best-characterized member, plays essential roles in the resistance to abiotic stress. This study reveals that the functionally redundant SYT1 and SYT3 genes, but not SYT5, are involved in salt and cold stress resistance. We also show that, unlike SYT5, SYT1 and SYT3 are not required for Pseudomonas syringae resistance . Since SYT1 and SYT5 interact in vivo via their SMP domains , the distinct functions of these proteins cannot be caused by differences in their localization. Interestingly, structural phylogenetic analysis indicates that SYT1 and SYT5 clades emerged early in the evolution of land plants. We also show that SYT1 and SYT5 clades exhibit different structural features, rationalizing their distinct biological roles.

The increased production and use of plastics have negative impacts on the environment. However, not only the polymers themselves, but also smaller particles used for instance in cosmetics or derived from decomposition are toxicologically relevant. In recent years, research has focused on the occurrence of micro- and nanoplastics (MNPs) in air, soil and water, whereas the entry into plants has hardly been investigated. To determine the load, translocation of MNPs and their effects on metabolism, pak choi, tomato, radish and asparagus have been exposed with fluorescent-labeled particles; poly(methyl methacrylate) (PMMA) or polystyrene (PS) of different sizes and surface modifications. By means of fluorescence microscopy the entry of NP regardless of their size (100 nm – 500 nm) and surface modification (unmodified, COOH or NH 2) has been demonstrated. Additionally, metabolic changes induced by MNPs have been determined by metabolomics. The entry could pose a potential risk to food safety as well as quality and needs greater concern and further research.

In Chlamydomonas, the directly light-gated, plasma membrane-localized (PM) cation channels channelrhodopsins ChR1 and ChR2 are the primary photoreceptors for phototaxis. Their targeting and abundance is essential for optimal movement responses. However, our knowledge how Chlamydomonas achieves this is still at its infancy. Here we show that ChR1 internalization occurs via light-stimulated endocytosis. Prior or during endocytosis ChR1 is modified and forms high molecular mass complexes. These are the solely detectable ChR1 forms in extracellular vesicles (EVs) and their abundance therein dynamically changes upon illumination. The ChR1-containing EVs are secreted via the PM and/or the ciliary base. In line with this, ciliogenesis mutants exhibit increased ChR1 degradation rates. Further, we establish involvement of two cysteine proteases in its turnover: CEP1, a papain-type C1A member, and a calpain. ΔCEP1 knock-out strains lack light-induced ChR1 degradation, whereas ChR2 degradation was unaffected. Low light stimulates CEP1 expression, which is regulated via phototropin, a SPA1 E3 ubiquitin ligase and cAMP. Further, mutant and inhibitor analyses revealed involvement of the small GTPase ARL11 and SUMOylation in ChR1 targeting to the eyespot and cilia. Our study thus defines the degradation pathway of this central photoreceptor of Chlamydomonas and identifies novel elements involved in its homeostasis and targeting.

Tree transpiration dynamics and mechanisms in karst habitats are not fully understood due to the heterogeneous environmental features and complex species composition. Two common coexisting tree species, Mallotus philippensis and Celtis biondii, were examined in soil- and rock-dominated (SD and RD) karst habitats. Soil moisture, plant transpiration, root distribution, and leaf water potential were measured over two years (2021 and 2022). The mean water content was significantly lower in the RD than in the SD habitat. Transpiration patterns also differed between habitats, although species-specific distinctions were driven by leaf and root physiological traits. M. philippensis showed an isohydric tendency in both habitats and a lower density of fine roots, mostly in the soil zone, in the RD habitat. The transpiration of M. philippensis followed the variation in soil moisture, being lower in the RD habitat. Conversely, an anisohydric tendency in both habitats and a higher density of fine roots in both the soil and bedrock zones in the RD habitat were found in C. biondii. This species showed higher transpiration in the RD habitat, arising from ample water availability from soil and epikarst. Our findings reveal the regulatory mechanisms of species-specific root-zone water availability in transpiration patterns across karst habitats.

The root cortex is an important anatomical phenes, and root cortical senescence (RCS) is closely associated with root absorptive function. However, characteristics and responses of RCS to drought stress in cotton have received little attention. This study subjected the drought-tolerant cotton variety “Guoxin 02” and the drought-sensitive variety “Ji 228” to drought stress (8% PEF6000) and no-stress (0% PEG6000) treatments to determine the characteristics and responses of cotton RCS to drought stress. The results showed that the RCS of the two varieties was significantly promoted under drought stress. The greater the distance from the root tip, the more severe the RCS occurrence under drought stress compared with non-stress treatment. The occurrence of RCS in “Guoxin 02” highered by 14.03%-20.18% compared to “Ji 228” under drought stress. Moreover, the RCS was significantly negatively correlated with root respiration but significantly positively correlated with total root length and leaf water potential ( p < 0.05). Indole-3-acetic acid (IAA) content increased, while abscisic acid (ABA) content decreased as the RCS increased. In summary, endogenous hormones regulated the occurrence of RCS, which reduced the root metabolic costs and seemingly achieved more resource redistribution to new roots, thereby expanding the water absorption capacity of roots to fully utilize deep water resources. Thus, the study demonstrates the potential of RCS in improving the drought stress tolerance of cotton.

Allotetraploid white clover formed during the last glaciation through hybridisation of two European diploid progenitors from restricted niches: one coastal, the other alpine. Here, we examine which hybridisation-derived molecular events may have underpinned white clover’s post-glacial niche expansion. We compared the transcriptomic frost responses of white clovers (inbred line and an alpine-adapted ecotype), extant descendants of its progenitor species and a resynthesised white clover neopolyploid to identify genes that were exclusively frost-induced in the alpine progenitor and its derived subgenomes. From these analyses we identified galactinol synthase, the rate-limiting enzyme in biosynthesis of the cryoprotectant raffinose, and found that the extant descendants of the alpine progenitor as well as the neopolyploid white clover rapidly accumulated significantly more galactinol and raffinose than the coastal progenitor under cold stress. The frost-induced galactinol synthase expression and rapid raffinose accumulation derived from the alpine progenitor likely provided an advantage during early post-glacial colonisation for white clover compared to its coastal progenitor.

Early sowing can help summer crops escape drought and can mitigate the impacts of climate change on them, but it exposes them to cold stress during initial developmental stages, which has both immediate and long-term effects on development and physiology. To understand how early night-chilling stress impacts plant development and the yield, we studied the reference sunflower line XRQ under controlled, semi-controlled and field conditions. We performed high-throughput imaging of the whole plant parts and obtained physiological and transcriptomic data from leaves, hypocotyls and roots. We observed morphological reductions in early stages under field and controlled conditions, with a decrease in root development, an increase in reactive oxygen species content in leaves and changes in lipid composition in hypocotyls. A long-term increase in leaf chlorophyll suggests a stress memory mechanism that was supported by transcriptomic induction of histone coding genes. We highlighted leaf transcriptomes in cold-acclimation genes such as chaperone, heat shock and late embryogenesis abundant proteins. We identified genes in hypocotyls involved in lipid, cutin, suberin and phenylalanine ammonia lyase biosynthesis and ROS scavenging. This comprehensive study describes new phenotyping methods and candidate genes to understand phenotypic plasticity better in response to chilling and study stress memory in sunflower.

Mesophyll conductance ( g m ) describes the efficiency with which CO 2 moves from substomatal cavities to chloroplasts. Despite the stipulated importance of leaf architecture in affecting g m , there remains a considerable ambiguity about how and whether anatomy influences g m . This is, in part, because studies exploring the relationship between leaf architecture and g m have often relied on simple linear or exponential models to identify correlations. Here, we employed non-linear machine learning models to more comprehensively assess the relationship between ten leaf architecture traits and g m . These models achieved excellent predictability of g m , which depended on the leaf architecture traits considered as predictors. Dissection of the importance of leaf architecture traits in the models indicated that cell wall thickness and chloroplast area exposed to internal airspace have a large impact on interspecific variation in g m . Additionally, other leaf architecture traits, such as: leaf thickness, leaf density, and chloroplast thickness emerged as important predictors of g m . We found significant differences in the predictability between models trained on different plant functional types (PFTs): those trained on woody species could predict g m by anatomical traits on other woody PFTs, ferns, and C 3 herbaceous plants, whereas the converse did not hold in general. By moving beyond simple linear and exponential models, our analyses demonstrated that a larger suite of leaf architecture traits drive differences in g m than has been previously acknowledged. These findings pave the way for modulating g m by strategies that modify its leaf architecture determinants.

Changes in leaf temperature are known to drive stomatal responses, because the leaf-to-air water vapor gradient (Δ w) increases with temperature if ambient vapor pressure is held constant, and stomata respond to changes in Δ w. However, the direct response of stomata to temperature (DRST; the response when Δ w is held constant by adjusting ambient humidity) has been examined far less extensively. Though the meager available data suggest the response is usually positive, results differ widely and defy broad generalization. As a result, little is known about the DRST. This review discusses the current state of knowledge about the DRST, including numerous hypothesized biophysical mechanisms, potential implications of the response for plant adaptation, and possible impacts of the DRST on plant-atmosphere carbon and water exchange in a changing climate.

Gummy stem blight (GSB), a severe and widespread disease causing great losses to cucurbit production, is a major threat to melon production. However, the melon-GSB interaction remains largely unknown, which significantly impedes the genetic improvement of melon for GSB resistance. Here, full-length transcriptome and widely targeted metabolome were used to reveal the early defense responses of resistant (PI511890) and susceptible (Payzawat) melon to GSB. Differentially expressed genes were specifically enriched in the secondary metabolite biosynthesis and MAPK signaling pathway in PI511890, while in carbohydrate metabolism and amino acid metabolism in Payzawat. More than 1000 novel genes were identified in PI511890, which were enriched in the MAPK signaling pathway. There were 11,793 alternative splicing events identified and involved the defense response to GSB. A total of 910 metabolites were identified, with flavonoids as the dominant metabolites. Integrated full-length transcriptome and metabolome analysis showed that eriodictyol and oxalic acid may be used as marker metabolites for GSB resistance in melon. Moreover, post-transcription regulation was widely involved in the defense response of melon to GSB. These results improve our understanding of the interaction between melon and GSB and may facilitate the genetic improvement of GSB resistance of melon.

Illuminated leaves assimilate CO 2 via gross photosynthesis and liberate CO 2 via photorespiration and ‘day respiration’, often denoted as R d. Day respiration is a minor CO 2-exchange component of net photosynthesis but is important for carbon use efficiency, computations of internal conductance, or the interpretation of net photosynthetic 12C/ 13C fractionation. Unfortunately, there is no simple method to measure R d and tracing the origin of C-atoms found in day-respired CO 2 is difficult. As a result, a common misconception is that day respiration is simply a catabolic, CO 2-producing flux through ordinary catabolism (glycolysis and Krebs ‘cycle’). In the past few years, considerable progress has been made in our understanding of day respiration. It appears that R d is a net flux resulting from several CO 2-generating and CO 2-fixing reactions, not only related to catabolism but also to anabolism (biosyntheses). In addition, there is now direct evidence that decarboxylating reactions are partly fed by carbon sources disconnected from current photosynthesis and this effect has consequences for isotopic mass-balance. Therefore, leaf day ‘respiration’ is much more than just CO 2 production by respiratory catabolism. Rather, it reflects whole metabolic orchestration of leaves from N fixation to secondary metabolism and it perhaps deserves another name, such as “day decarboxylations”.

While dynamic regulation of photosynthesis in fluctuating light is increasingly recognized as an important driver of carbon uptake, acclimation to realistic patterns of light fluctuations is still largely unexplored. We subjected Arabidopsis thaliana (L.) plants to light fluctuations with distinct amplitudes and average irradiance. Using gas-exchange and thermal imaging, we examined how light fluctuations affected leaf structure, photosynthetic capacity, and water relations. We found a wider amplitude of fluctuations produced a stronger acclimation response. Large reductions of leaf mass per area under fluctuating light framed our interpretation of changes in pigment content and photosynthetic capacity, in that photosynthetic investment increased markedly on a mass basis, but only a little on an area basis. Moreover, leaf transpiration rose sharply, being nearly four times under fluctuating light. Our findings indicate that leaves growing under fluctuating light, although thinner, maintained their photosynthetic capacity; suggesting their photosynthesis may be more cost-efficient than those under steady light, but overall may incur increased maintenance costs. This is especially relevant for plant performance globally, because naturally fluctuating light created conflicting acclimation cues for photosynthesis and transpiration that may hinder progress towards ensuring food security under climate-related extremes of water stress.

Singlet Oxygen (SO) is among the most potent reactive oxygen species, and readily oxidizes proteins, lipids, and DNA. It can be generated at the plant surface by phototoxins in the epidermis, acting as a direct defense against pathogens and herbivores (including humans). SO can also accumulate within mitochondria, peroxisomes, cytosol, and the nucleus through multiple enzymatic and non-enzymatic processes. However, the primary location of SO in plants is in the chloroplast, where it results from transfer of light energy from PhotosystemII to triplet oxygen. SO accumulates in response to diverse stresses that perturb chloroplast metabolism, and while its short half-life precludes exiting the chloroplast, it participates in retrograde signaling through the EXECUTER1 sensor, generation of carotenoid metabolites, and possibly other unknown pathways. SO thereby reprograms nuclear gene expression and modulates hormone signaling and programmed cell death. While SO signaling has long been known to regulate plant responses to high-light stress, recent literature also suggests a role in plant interactions with insects, bacteria, and fungi. The goals of this review are to provide a brief overview of SO, summarize evidence for its involvement in biotic stress responses, and discuss future directions for the study of SO in signaling and defense.

Drought threatens plant growth and related ecosystem services. The emergence of plant drought stress under edaphic drought is well studied, whilst the importance of atmospheric drought only recently gained momentum. Yet, little is known about the interaction and relative contribution of edaphic and atmospheric drought on the emergence of plant drought stress. We conducted a gradient experiment, fully crossing gravimetric water content (GWC: field capacity-permanent wilting point) and vapour pressure deficit (VPD: 1-2.25kPa) using five wheat varieties from three species ( Triticum monococcum, T. durum & T. aestivum). We quantified the emergence of plant drought stress on molecular (ABA), cellular (stomatal conductance), organ (leaf water potential) and stand level (evapotranspiration). Plant drought stress increased with decreasing GWC across all organisational levels. This effect was magnified non-linearly by VPD after passing a critical threshold of soil water availability. At around 20% GWC plants lost their ability to regulate leaf water potential via stomata regulation, followed by the emergence of hydraulic dysfunction. The emergence of plant drought stress is characterized by changing relative contributions of soil vs. atmosphere and their non-linear interaction. This highly non-linear response, consequently, is likely to abruptly alter plant-related ecosystem services in a drying world.

Due to their stationery nature, plants are exposed to a diverse range of biotic and abiotic stresses, of which heavy metals stress poses as one of the most detrimental abiotic stresses, targeting crucial and vital processes. Heavy metals instigate the over-production of reactive oxygen species (ROS), and in order to mitigate the adverse effects of ROS, plants induce multiple defence mechanisms. Besides the negative implications of overproduction of ROS, these molecules play a multitude of signaling roles in plants, acting as a central player in the complex signaling network of cells. One of the signaling mechanisms it is involved in is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used to transduce extracellular stimuli into intracellular responses. Plant MAPKs have been implicated in signaling of stresses, phytohormones and cell cycle cues. However, the influence of various heavy metals on MAPKs activation has not been well documented. In this review, we will attempt to address and summarize several aspects related to various heavy metal-induced ROS signaling, how these signals activate the MAPK cascade and the downstream transcription factors that instigates the plants response to these heavy metals. Moreover, we will highlight a modern research methodology that could characterize the novel genes associated with MAPKs and their roles in heavy metal stress.