Although cell wall polymers play important roles in the tolerance of plants to abiotic stress, the effects of salinity on cell wall composition and metabolism in grasses remain largely unexplored. Here, we conducted an in-depth study of changes in cell wall composition and phenolic metabolism induced upon salinity in maize seedlings and plants. Cell wall characterization revealed that salt stress modulated the deposition of cellulose, matrix polysaccharides and lignin. The extraction and analysis of arabinoxylans by size-exclusion chromatography, two-dimensional NMR spectroscopy and carbohydrate gel electrophoresis showed a reduction of arabinoxylan content in salt-stressed roots, with no changes in xylose/arabinose ratios. Saponification and mild acid hydrolysis followed by RP-HPLC analysis revealed that salt stress also reduced the feruloylation of arabinoxylans. Determination of lignin content and composition by nitrobenzene oxidation and two-dimensional NMR confirmed the increased incorporation of syringyl units in lignin polymer. Our data also revealed the induction of the expression of genes and enzymes enrolled in phenylpropanoid biosynthesis under salinity. The UPLC-MS-based metabolite profiling confirmed the modulation of phenolic profiling by salinity and the accumulation of ferulate and its derivatives 3- and 4-O-feruloyl quinate. In conclusion, we present a model for explaining cell wall remodeling in response to salinity.

Examining how plant traits respond to and affect herbivory is a common approach to exploring plant-herbivore interactions and their impact on ecosystem processes and functioning. Despite plants being potentially exposed to both vertebrate and invertebrate herbivores simultaneously, fundamental differences in the ecology and evolution of these two herbivore guilds results in them often being studied separately. A synthesis of the literature is needed to understand the types of plant traits examined and their response to, and effect on (in terms of forage selection) vertebrate and invertebrate herbivory, and to identify associated knowledge gaps. Focusing on grassland systems and species, we found 139 articles that met our criteria: 40 invertebrate, 97 vertebrate and 2 focussed on both vertebrate and invertebrate herbivores. Invertebrate focussed research, research conducted in the Southern Hemisphere and research on non-domesticated herbivores was significantly underrepresented based on our search. Differences in study focus (trait response or trait affect), along with considerable differences in the types of traits examined, led to limited capacity for comparison between the two herbivore guilds. For both invertebrates and vertebrates however, plant traits related to growth, such as leaf nitrogen and photosynthetic capacity, were often positively associated with herbivory. Future research should prioritise understanding how invertebrates, and the combined impact of both invertebrates and vertebrates’ respond to and affect plant traits. This review can be used as a guide for future research to select plant traits which are commonly measured either within one, or across both guild/s, as to help improve comparability and the broader significance of results, while also extending research breadth and knowledge.

Plants can detect neighbouring plants through a reduction in the ratio between red and far-red light (R:FR). This provides a signal of plant-plant competition and induces rapid plant growth while inhibiting defence against biotic stress, two interlinked responses designated as the shade avoidance syndrome (SAS). Consequently, the SAS can influence plant-herbivore interactions that could cascade to higher trophic levels. However, little is known on how the expression of the SAS can influence tritrophic interactions. We investigated whether changes in R:FR affect the emission of herbivore-induced plant volatiles (HIPVs), and whether these changes influence the attraction of the zoophytophagous predator Macrolophus pygmaeus. We also studied how the expression of the SAS and subsequent inhibition of plant defences affects the reproduction of M. pygmaeus in both the presence and absence of the greenhouse whitefly ( Trialeurodes vaporariorum) as arthropod prey. The results show that changes in R:FR have little effect on HIPV emissions and predator attraction. However, a reduction in R:FR leads to increased reproduction of both the predator and the whiteflies. We conclude that shade avoidance responses can increase the population development of M. pygmaeus directly by reducing plant defences, and indirectly by supporting higher herbivore densities.

CO 2-induced chloroplast movement was reported in the monograph by Gustav Senn in 1908: unilateral CO 2 supply to the one cell-layered moss leaves induced the positively CO 2-tactic periclinal arrangement of chloroplasts. However, from the modern criteria, several experimental settings are unacceptable. Here, using a model moss plant Physcomitrium patens, we examined basic features of chloroplast CO 2-tactic relocation with a modernized experimental system. The CO 2 relocation was light-dependent and especially the CO 2 relocation in red light was substantially dependent on photosynthetic activity. Between the cytoskeletons responsible for chloroplast movement of P. patens, the microfilament mainly worked for CO 2 relocation, but the microtubule-based movement was insensitive to CO 2. The CO 2 relocation was induced not only by air with and without CO 2 but also by the more realistic difference in CO 2 concentration between the two sides. In the leaves placed on the surface of a gel sheet, chloroplasts avoided the gel side and positioned in the air facing surface. This was also shown to be photosynthesis dependent. Based on these observations, we propose a working hypothesis that the threshold light intensity between the light-accumulation and -avoidance responses of the photorelocation would be increased by CO 2, resulting in the CO 2-tactic relocation of chloroplast.

The linkage of stomatal behavior with photosynthetic processes is critical to understanding water and carbon cycles under global change. The slope ( g1) of stomatal conductance ( gs) versus CO 2 assimilation ( Anet) serves as a proxy of the marginal water cost of carbon acquisition and the trade-off between carbon gain and water loss. Here we use g1 to assess species differences in the response of stomatal behavior to experimental climate change manipulations, asking whether generalizable patterns exist across species and climate contexts. A total of 17,727 Anet- gs measurements made in a long-term open-air experiment under ambient and +3.3°C warming, and ambient and ~40% summer rainfall reduction provided > 2,700 estimates of g1 across 21 boreal and temperate tree species. All species became more conservative in their water use (lower g1) in warming and/or reduced rainfall treatments because of lower soil moisture. In contrast to these phenotypic responses, species from warmer and drier habitats tended to have slightly higher g1 and to be the least sensitive to the decrease in soil water. Overall, both warming and rainfall reduction consistently made stomatal behavior more conservative in terms of water loss per unit carbon gain across 21 species and a decade of experimental observation.

As sessile organisms, plants are constantly challenged by a dynamic growing environment. This includes fluctuations in temperature, water availability, light levels, and atmospheric conditions. In concert with changes in abiotic conditions, plants experience changes in biotic stress pressures, including plant pathogens, viruses, and herbivores. Human-induced increases in atmospheric carbon dioxide (CO 2) levels have led to alterations in plant growth environments that challenge their productivity and nutritional quality. Additionally, it is predicted that climate change will alter the prevalence and virulence of plant pathogens, further challenging plant productivity. A knowledge gap exists in the complex interplay between plant responses to biotic and abiotic stress conditions. Closing this gap is crucial for developing climate resilient crops in the future. Here, we review the physiological responses of plants to elevated CO 2, temperature, tropospheric ozone (O 3), and drought conditions, as well as the interaction of these abiotic stress factors with plant pathogen pressure. Additionally, we describe the crosstalk and trade-offs involved in plant responses to both abiotic and biotic stress, and outline targets for future work to develop a more sustainable future food supply in light of future climate change.

Various root-colonizing bacterial species can promote plant growth and trigger systemic resistance against aboveground leaf pathogens and herbivore insects. To date, the underlying metabolic signatures of these rhizobacteria-induced plant phenotypes are poorly understood. To identify core metabolic pathways that are targeted by growth-promoting rhizobacteria, we used combinations of three plant species and three rhizobacterial species and interrogated plant shoot chemistry by untargeted metabolomics. A substantial part (50-64%) of the metabolites detected in plant shoot tissue was differentially affected by the rhizobacteria. Among others, the phenylpropanoid pathway was targeted by the rhizobacteria in each of the three plant species. Differential regulation of the various branches of the phenylpropanoid pathways showed an association with either plant growth promotion or growth reduction. Overall, suppression of flavonoid biosynthesis was associated with growth promotion, while growth reduction showed elevated levels of flavonoids. Subsequent assays with twelve Arabidopsis flavonoid biosynthetic mutants revealed that the proanthocyanidin branch plays an essential role in rhizobacteria-mediated growth promotion. Our study also showed that a number of pharmaceutically and nutritionally relevant metabolites in the plant shoot were significantly increased by rhizobacterial treatment, providing new avenues to use rhizobacteria to tilt plant metabolism towards the biosynthesis of valuable natural plant products.

Xylem embolism resistance varies across species influencing drought tolerance, yet little is known about the determinants of the embolism resistance of an individual conduit. Here we conducted an experiment using the optical vulnerability method to test whether individual conduits have a specific water potential threshold for embolism formation and whether pre-existing embolism in neighbouring conduits alters this threshold. Observations were made on a diverse sample of angiosperm and conifer species through a cycle of dehydration, rehydration and subsequent dehydration to death. Upon rehydration after the formation of embolism, no refilling was observed. When little pre-existing embolism was present, xylem conduits had a conserved, individual, embolism resistance threshold that varied across the population of conduits. The consequence of a variable conduit-specific embolism threshold is that a small degree of pre-existing embolism in the xylem results in an apparently more resistant xylem in a subsequent dehydration, particularly in angiosperms with vessels. While our results suggest that pit membranes separating xylem conduits are critical for maintaining a conserved individual embolism threshold for given conduit when little pre-exisiting embolism is present, as the percentage of embolized conduits increases, gas movement, local pressure differences, and connectivity between conduits increasingly contribute to embolism spread.

The coordination of plant leaf water potential (ΨL) regulation and xylem vulnerability to embolism is fundamental for understanding the tradeoffs between carbon uptake and risk of hydraulic damage. There is a general consensus that trees with vulnerable xylem regulate ΨL more conservatively than plants with resistant xylem. We evaluated if this paradigm applied to three important eastern US temperate tree species, Quercus alba L., Acer saccharum Marsh., and Liriodendron tulipifera L., by synthesizing 1600 ΨL observations, 122 xylem embolism curves, and xylem anatomical measurements across ten forests spanning pronounced hydroclimatological gradients and ages. We found that, unexpectedly, the species with the most vulnerable xylem (Q. alba) regulated ΨL less strictly than the other species. This relationship was found across all sites, such that coordination among traits was largely unaffected by climate and stand age. Quercus species are perceived to be among the most drought tolerant temperate US forest species; however, our results suggest their relatively loose ΨL regulation in response to hydrologic stress occurs with a substantial hydraulic cost that may expose them to novel risks in a more drought-prone future. We end by discussing mechanisms that allow these species to tolerate and/or recover from hydraulic damage.

The biosynthesis of anthocyanins has been shown to be influenced by light quality. However, the molecular mechanisms underlying the light-mediated regulation of fruit anthocyanin biosynthesis are not well understood. In this study, we analyzed the effects of supplemental red and blue light on the anthocyanin biosynthesis in non-climacteric bilberry (Vaccinium myrtillus L.). After six days of continuous irradiation during fruit ripening, both red and blue light elevated concentration of total anthocyanins, but especially red light promoted accumulation of delphinidins. Transcriptomic analysis of ripening berries showed that both light treatments up-regulated all the major anthocyanin structural genes, the key regulatory MYB transcription factors and abscisic acid (ABA) biosynthetic genes. However, higher induction of specific genes of anthocyanin and delphinidin biosynthesis alongside ABA signal perception and metabolism were found in red light. The difference in red and blue light signaling was found in NCED, ABA receptor PYL and catabolic ABA-8’hydroxylase gene expression. Red light also up-regulated expression of SNARE domain transporters, which may indicate involvement of these proteins in vesicular trafficking of anthocyanins during fruit ripening. Our results suggest differential signal transduction and transport mechanisms between red and blue light in in ABA- regulated anthocyanin and delphinidin biosynthesis during non-climacteric fruit ripening.

Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating interspecific and intraspecific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin vs. non-kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behavior, allelochemical production, and soil microbial community composition, as well as carbon and nitrogen partitioning in the weeds. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non-kin mixtures. The effect was driven by kin recognition that induced altered root placement, established similar soil microbial communities, and altered weed carbon and nitrogen partitioning. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighboring collaborators (kin) or competitors and then adjust their growth, competitiveness and chemical defense accordingly.

This article comments on: ‘Short- and long-term effects of fire on stem hydraulics in Pinus ponderosa saplings’ by Partelli-Feltrin et al. (2020), https://doi.org/10.1111/pce.13881.

Summary: The hindrance of kernel development caused by waterlogging stress (WS) is the direct reason for the peanut yield reduction. Currently, the mechanism of kernel filling responding to WS remains unknown. The waterlogging-sensitive variety Huayu 39 was subjected to WS for 3 days after 7 days after gynophores touched the ground (DAG), and the key stage of WS affecting kernel filling is 14, 21, and 28 DAG. WS decreased the average filling rate and kernel dry weight. Therefore, transcriptome sequencing and widely-targeted metabolomic analysis were conducted on kernel to elucidate the mechanism for the decrease in average filling rate under WS, revealing that overexpression of the gene encoding tryptophan decarboxylase ( AhTDC), which caused the accumulation of melatonin, reduced kernel weight. The sucrose transformation rate was limited by the crosstalk between melatonin and ethylene, thereby reducing the kernel filling rate and hindering kernel development. Our results are crucial for formulating measures to alleviate the negative impact of WS on peanut yield and quality, providing a basis for exploring high-yield and high-quality cultivation, molecular-assisted breeding, and waterlogging prevention.

In plants, salicylic acid (SA) hydroxylation regulates SA homoeostasis, playing an essential role during plant development and response to pathogens. This reaction is catalyzed by SA hydroxylase enzymes, which hydroxylate SA producing 2,3- dihydroxybenzoic acid (2,3-DHBA) and/or 2,5-dihydroxybenzoic acid (2,5-DHBA). Several SA hydroxylases have been recently identified and characterized from different plant species; however, no such activity has been previously reported in maize. In this work, we describe the identification and characterization of a new SA hydroxylase in maize plants. This enzyme, with high sequence similarity to previously described SA hydroxylases from Arabidopsis and rice, converts SA into 2,5-DHBA; however, it shows different kinetics properties to those from previously characterized enzymes, and it also catalyzes the conversion of the flavonoid dihydroquercetin into quercetin in in vitro activity assays, suggesting that the maize enzyme may have different roles in vivo as those previously reported from other species. Despite this, ZmS5H can complement the resistance to pathogen and early senescence phenotypes of Arabidopsis s3h mutant plants. Finally, we characterized a maize mutant in the S5H gene ( s5hMu) that has altered growth, senescence and increased resistance against Colletotrichum graminicola infection, showing not only changes in SA and 2,5-DHBA but also variations in flavonol levels. Together, the results presented here provide evidence that SA hydroxylases in different plant species have evolved to show differences in catalytic properties that may be important to fine tune SA levels and other phenolic compounds such as flavonols to regulate different aspects of plant development and defense against pathogens.

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.

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.

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”.

With continued global warming, plants are forecast to increasingly experience abiotic stress(es). Stomata on leaf surfaces are the gatekeepers to plant interiors, regulating gaseous exchanges that are crucial for both photosynthesis and outward water release. To optimise future productivity, accurate modelling of how stomata govern plant-environment interactions will be crucial. Here, we synergise optical and thermal imaging data to enhance transpiration modelling during water and/or nitrogen stress. By utilising hyperspectral data and partial least squares regression analysis of six plant traits and fluxes in wheat ( Triticum aestivum), we have developed a new spectral vegetation index; the combined nitrogen and drought index (CNDI), which can be used to detect both water stress and/or nitrogen deficiency. Upon full stomatal closure during drought, CNDI reduces as leaf biochemistry changes unfold, and during a combined stress experiment (drought and nitrogen deficiency), this is reflected in CNDI showing a strong relationship with leaf relative water content ( r2 = 0.70). By incorporating CNDI transformed with a sigmoid function into thermal-based transpiration modelling, we have increased the accuracy of modelling water fluxes during abiotic stress. If employed using future remote sensing technologies, our findings have the potential to markedly improve agricultural water usage and yields.