Plant, Cell & Environment

Leaf gas exchange is the key driver of forest carbon uptake and directly determines forest carbon sink activity. Additionally, plants release a variety of biogenic volatile organic compounds (VOCs) acting as stress signals of trees. However, continuous hourly resolved measurements of leaf gas exchange and VOC emissions in tall tree canopies are challenging and remain scarce. To this end, we developed a sophisticated in-situ leaf gas exchange measurement system with 24 cuvettes deployed on mature Fagus sylvatica (n=3) and Pseudotsuga menziesii (n=3) individuals in a mixed temperate forest. We additionally measured sap flux density (Js), radial growth and tree water deficit (TWD) to gain a holistic picture of seasonal leaf and stem water and carbon flux dynamics during the summer of 2024. During midsummer, we found a gradual reduction of stomatal conductance (gs) and VOC emissions of sun, but not shade branchlets of P. menziesii in response to moderate atmospheric and edaphic drying. Decreased gs led to a downregulation of transpiration (E), Js, and carbon isotope discrimination accompanied by an increase in TWD and intrinsic water used efficiency. Leaf gas exchange of shade branchlets remained unaffected due to microclimatic buffering effects. Contrarily, sun leaves of F. sylvatica, profited from sunny midsummer conditions and increased leaf gas exchange, whereas shade leaves benefitted from more diffuse light during early summer exhibiting similar carbon assimilation, transpiration and VOC emissions as sun leaves. For both species we found a clear time lag of four to five hours between maximum leaf and stem water fluxes and a delay of up to 20 hours for the recovery of TWD, highlighting the role of stem water reserves. Pronounced seasonal and diurnal differences of leaf gas exchange, stem water fluxes and VOC emissions showed, that continuous data are essential to better understand variability of ecosystem flux dynamics.

Residual water losses after stomatal closure have recently been identified as key determinants of drought-induced hydraulic failure, particularly under heatwave conditions. However, little is known about the intraspecific variability of residual conductance (gres) and its thermal sensitivity. Here, we investigated the genetic and environmental sources of variation in gres and its associated thermal parameters (phase transition temperature T_, and temperature sensitivities Q10a and Q10b) in Abies alba Mill., together with vulnerability to xylem embolism (P50). Measurements were performed using the Drought-Box on seven French provenances grown in a common garden to assess genetic variability, and on trees growing across contrasting forest sites to quantify phenotypic plasticity. Seasonal dynamics and within-canopy microclimatic effects were also examined, and linked to needle biochemical traits. Residual conductance exhibited a marked seasonal decline, with high values in newly formed needles followed by a stabilization from late summer to the following spring, closely tracking the accumulation of cuticular waxes. In contrast, Klason lignin content showed little seasonal variation. Difference between provenances was weak for all investigated parameters, suggesting strong constraints on these safety-related traits. By contrast, gres showed significant environmental plasticity, with lower values at more climatically constrained sites, while thermal parameters and P50 remained relatively conserved. Our results identify gres as a developmentally dynamic and environmentally plastic trait in silver fir, potentially representing a key lever of acclimation to drought. Incorporating such variability into mechanistic models should improve predictions of tree vulnerability under future climates combining intensified droughts and heatwaves. Key message.Residual conductance in Abies alba is developmentally dynamic and environmentally plastic but genetically constrained, highlighting its key role in acclimation to drought and heatwave-driven hydraulic failure.

Woody stems conduct both photosynthetic assimilation and respiration. The two processes work in concert, as stem photosynthesis helps refix CO2 released by stem respiration, thereby increasing carbon-use efficiency and generating a local pool of non-structural carbohydrates supporting cambial growth and stem hydraulic function. Despite its importance, little is known about seasonal variation in stem photosynthesis and the factors underlying its activity throughout the season. To fill this gap, we measured stem gas exchange together with growth activity, water status and photosynthetic pigment contents in two temperate species, Acer platanoides L. and Prunus avium L., over the season. In both species, gross photosynthetic rates (Pg) and dark respiration (Rd) changed significantly over the season in a similar pattern, indicating strong coordination between the two processes. Both Pg and Rd reached the highest values in May, during the period of rapid leaf expansion and secondary growth, and declined later in the growing season. At each measurement date, Rd exceeded Pg, resulting in a net CO2 efflux from the stems. The seasonal changes in Pg and Rd translated into seasonal variability in relative refixation of CO2, ranging from 3 to 59% and gradually decreasing towards the end of the season. Additionally, the Pg corresponded with the tissue hydration and increased significantly with increasing stem water potential. In contrast, total chlorophyll content showed less pronounced seasonal variation and thus explained substantially lower seasonal variability in Pg, except for the chlorophyll a/b ratio, which changed dynamically over the season and reached a minimum during the peak of the growing season. Overall, our results reveal that stem photosynthesis varies seasonally in accord with stem growth and water status, while the chlorophyll content has a lower impact on the seasonal changes. These findings are important for our understanding of the carbon relations of trees.

Plants acclimate to mechanical stimuli such as touch and wind via thigmomorphogenesis, a suite of developmental responses that alter their growth and architecture. However, the early signaling mechanisms translating mechanoperception into long-term morphological changes remain incompletely understood. We investigated the role of the rapidly touch-induced transcription factor RRTF1 (REDOX RESPONSIVE TRANSCRIPTION FACTOR 1) in these processes. Phenotypically, under aggressive mechanical stimulation, rrtf1 mutant exhibited attenuated stunting (less height reduction). This suggests a key role for RRTF1 in promoting thigmomorphogenic responses under severe mechanical stimuli, though the rrtf1 mutant responded similarly to wild-type under gentle, repeated brushing. The alleviation of growth stunting in rrtf1 was largely jasmonic acid (JA)-independent. Transcriptome analysis at 10 minutes post-touch revealed that rrtf1 mutant maintained approximately 86% of wild-type touch-responsive gene expression. Nevertheless, RRTF1 modulated specific regulons, partly through an interplay with WRKY transcription factors, as evidenced by altered TF binding motif enrichment in RRTF1-specific differentially expressed genes. We conclude that RRTF1 acts as a modulator of early touch signaling in Arabidopsis shoots. It is not essential for the bulk of the initial transcriptional response but fine-tunes specific gene sets and plays a crucial role in calibrating long-term thigmomorphogenic development, particularly by promoting growth inhibition under severe mechanical stimulation. This study provides insights into the alleviation of touch-induced growth inhibition in rrft1 mutant, which might be relevant to breeding for crops that are planted in high density and experience constant physical contact with neighboring plants.

- Norway spruce (Picea abies) dominates many European mountain forests, yet their seasonal water uptake strategies in high-elevation mono-specific natural stands remain poorly understood. We quantified contributions of shallow (0-10 cm) and deep (50-70 cm) soil layers to tree water uptake over three consecutive growing seasons (2020-2022) using stable water isotopes and Bayesian mixing analysis. - Contrary to the prevailing view of spruce as a shallow-rooted species relying primarily on water from the upper 10-20 cm of soil, our results showed more than 50% water uptake from deeper soil (50-70 cm), with deeper soil contributions crossing 80% in 2020. - During the dry and warm summer of 2022, positive soil recharge and elevated atmospheric demand increased evapotranspiration, with spruce trees taking up recently infiltrated rainfall from different soil depths, including >50% uptake from deeper layers. - Spruce water uptake shifted from cold-season-recharged soil water early in the growing season to warm-season precipitation in late summer. The timing of this shift in mid-summer can be explained by soil water recharge from recent rainfall infiltrated into the entire soil profile. This reliance on summer precipitation increases vulnerability of mono-specific spruce stands to more frequent droughts and heat waves under future climate change.

Bud outgrowth is a major component of plant architectural plasticity and is influenced by light conditions. While the inhibitory effect of low light intensity on branching is well documented, the underlying regulators remain debated and, especially, the role of sugar availability has never been thoroughly evaluated. Here, we combined experiments with a computational approach quantifying carbon source-sink balance in single-axis rose plants to investigate how continuous and transient light limitation regulate bud outgrowth. Continuous low light reduced photosynthesis, leading to decreased sugar availability and inhibited bud outgrowth. In contrast, a transient period of low light followed by high light unexpectedly stimulated bud outgrowth, shortened the delay between outgrowth of successive buds, and produced an over-branched phenotype. This response resulted from a non-reversible reduction in the growth of apical organs appearing under low light, which lowered carbon demand and caused sugar over-accumulation after the return to high light. Manipulating carbon supply and demand through leaf masking, photosynthetic inhibition, and targeted sucrose feeding causally confirmed the central role of sugar availability in these contrasting responses. Beyond these findings, key requirements for models simulating branching plasticity were identified and this work provides a basis for predicting branching responses under fluctuating and complex light environments. HighlightBud outgrowth, a key component of plant plasticity, is regulated by light intensity through sugar availability. Continuous and transient low light have opposite effects by limiting sugar production and use, respectively.

BackgroundNon-optimal temperatures have become a major constraint on plant development under rapidly changing climatic conditions. Both sub- and supra-optimal temperatures reduce physiological activity, alter plant morphology, lead to plant mortality, and ultimately decrease crop productivity. Temperature-tolerant plants employ physiological and morphological mechanisms to mitigate such stress. In this study, we aimed to identify the source of temperature tolerance in warm-climate adapted melon (Cucumis melo L.). ResultsSuboptimal temperature-tolerant accession (Ananas Yoqneam; AY) and susceptible accession (PI414723) were reciprocally grafted and grown under controlled temperature regimes of 16 {degrees}C, 25 {degrees}C, and 35 {degrees}C. Physiological and morphological traits were measured to characterize tolerance mechanisms and whole-plant responses. Temperature emerged as the dominant factor governing plant performance. Whereas non-grafted parental lines maintained consistent differences across all temperature regimes, reciprocal graft combinations diverged mainly under suboptimal (16 {degrees}C) conditions. Under these temperatures, scion identity strongly determined whole-plant performance through biochemical limitations. ConclusionThese results highlight the importance of scion-derived traits in abiotic stress tolerance and their downstream influence on root function.

Light wavelengths modulate plant growth, metabolism, and physiology. Amaranthus, a C4 underutilized climate resilient crop with promising nutritional properties remained unexplored in terms of metabolite enrichment under monochromatic light wavelengths of visible spectrum. In current study, two cultivars of Amaranthus tricolor (green and red) were exposed to seven light regimes of photosynthetically active radiation (PAR; 400-700 nm): deep blue, blue, green, amber, red, deep red, far red, and their metabolic responses were captured using Gas Chromatography-Mass Spectrometry. The metabolic analysis revealed wavelength-specific reprogramming in the levels of organic acids, sugars, amino acids, fatty acids as well as phenolics. In both the green and red Amaranthus, branched-chain amino acids and phenylalanine, which are nutritionally essential, were significantly elevated under far-red light. While the phenolics such as caffeic acid and ferulic acid were elevated under green and deep blue light respectively in green Amaranthus, amber light wavelengths enhanced these phenolics in red Amaranthus. The study highlighted cultivar-specific metabolic rewiring triggered by specific wavelengths. Altogether, these findings provides insights into metabolic adaptation and demonstrate the ability of light wavelength to specifically enrich the targeted metabolite of nutritional relevance in Amaranthus. It offers strategies to improve the nutritional value of crops in controlled agriculture systems. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=167 HEIGHT=200 SRC="FIGDIR/small/714947v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@1a4477dorg.highwire.dtl.DTLVardef@518550org.highwire.dtl.DTLVardef@7682dorg.highwire.dtl.DTLVardef@4876e2_HPS_FORMAT_FIGEXP M_FIG C_FIG

Increasing frequency of drought under climate change threatens crop production and intensifies pest pressures, yet the interactive effects of drought and herbivory on plant metabolism and ecological outcomes remain incompletely understood. We subjected sugar beet (Beta vulgaris) plants to moderate and high drought, alone or with infestation by the beet leaf miner (Pegomya cunicularia), and analyzed plant physiology, central metabolites, and volatile organic compound (VOC) emissions. Drought alone reduced growth and photosynthetic efficiency, while combined stress led to accentuated metabolic reprogramming, including increased amino acids and organic acids, and a concurrent suppression and alteration of VOC emissions, especially in plants affected by high drought and leaf mining. The resulting changes in VOC blends reduced plant attractiveness to ovipositing females, leading to fewer eggs laid on severely stressed plants. Contrastingly, moderate drought generated a nutrient-rich environment: larvae feeding on these plants exhibited the highest growth rates, larger pupae and adults, and increased feeding damage. High drought strongly limited both plant water content and larval development. These findings reveal a stress-dependent tradeoff between enhanced leaf nutritional quality and reduced host detectability, underscoring the importance of integrating multi-stress plant biology for future pest management and crop resilience. HighlightCombined drought and herbivory in sugar beet plant triggered stress-intensity-dependent trade-offs between leaf nutritional quality and volatile emissions, affecting beet leaf miner performance and oviposition--highlighting how multi-stress interactions shape plant-insect dynamics. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/708914v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@1d92105org.highwire.dtl.DTLVardef@70693org.highwire.dtl.DTLVardef@140dc82org.highwire.dtl.DTLVardef@14cf411_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG

The source{square}sink attenuation hypothesis suggests that plants regulate carbon fixation in response to fluctuations in sink demands. Many evergreen trees exhibit flushing growth patterns, where new shoot development generates a strong, transient demand for both carbon and nitrogen that may influence the function of mature leaves. This study examined the source-sink attenuation hypothesis in the context of vegetative sink growth by investigating the photosynthetic capacity and nitrogen dynamics in mature citrus leaves across three stages of flush development. In contrast to expectations, photosynthesis declined as flush growth progressed. Early flush initiation induced stomatal limitation in mature leaves, whereas as sink demand from further shoot growth continued carboxylation capacity and Rubisco abundance declined, despite relatively stable total leaf nitrogen. These results suggest that mature leaves undergo selective protein retooling under prolonged sink demand, constraining CO{square} fixation while maintaining C export. Overall, this study revealed that under strong combined N and C sink demands, mature citrus leaves function primarily as regulated carbon conduits rather than dynamically upregulating photosynthesis, providing new insight into source-sink coordination in woody perennial species. HighlightCitrus flush growth shows that mature leaves suppress photosynthesis through stomatal and biochemical regulation while reallocating carbon and nitrogen to support new shoot development, challenging classic source-sink theory.

Photosynthesis accounts for most of the final grain yield in rice, making improvements in radiation use efficiency (RUE) a key strategy for enhancing productivity. Agronomically, RUE is defined as the biomass produced per unit of total solar radiation or photosynthetically active radiation intercepted by the canopy. However, the interaction between carbon and nitrogen metabolism plays a critical role in determining plant growth and grain yield. Assimilated nitrogen is required for the synthesis of photosynthetic pigments and enzymes, while the reduction of nitrate (NOLL) and nitrite (NOLL), as well as the assimilation of ammonium (NHLL), depend on the reducing power and carbon skeletons generated by photosynthesis. In this study, two high-yielding rice (Oryza sativa) cultivars--an indica-type (El Paso 144) and a japonica-type (INIA Parao) were subjected to two nitrogen treatments (3 mM and 9 mM NOLL/NHLL) and two light intensities (850 and 1500 mol mL{superscript 2} sL{superscript 1}). A strong interaction between light intensity and nitrogen metabolism was observed, with contrasting responses between subspecies. These differences reflect a coordinated regulation of carbon assimilation and primary nitrogen metabolism. The results provide new insights into the metabolic strategies underlying nitrogen compound accumulation under variable irradiance. Such knowledge is essential for improving nitrogen fertilizer use efficiency and yield performance in elite rice genotypes cultivated under commercial field conditions.

Processing of ribosomal RNA (rRNA) is essential for ribosome biogenesis, translation, plant development, and stress adaptation. Ribosome processing factor-2 (RPF2), which plays a role in the later stages of rRNA maturation, interacts with ribosomal protein L10A (RPL10A). RPF2 overexpression in Arabidopsis and Nicotiana benthamiana showed enhanced plant growth and trichome development due to increased gibberellic acid (GA) levels. Conversely, RPF2-silenced and mutant plants had a dwarf phenotype, reduced stomatal apertures, and decreased glucosinolate accumulation. RPF2 silenced and mutant plants also showed compromised nonhost disease resistance, whereas RPF2 overexpression lines exhibited enhanced disease resistance to both host and nonhost pathogens. RPL10A and RPF2 overexpression lines were sensitive to abscisic acid (ABA) and tolerant to drought, which is attributed to their unique roles in translation regulation. Despite having larger stomatal apertures, RPF2 overexpression plants displayed low pathogen multiplication rates and reduced water loss, indicating independent resistance mechanisms associated with ribosomal functions in translation regulation. Although both RPL10A and RPF2 proteins interact with each other and are involved in translation regulation, proteomic analysis suggests that they regulate the translation of distinct sets of genes during pathogen or drought stress. These findings indicate that RPF2 and RPL10A play independent roles in the regulation of unique protein translation.

Belowground, plants are exposed to a wide range of biotic stresses that vary in severity and nature, including tissue damage, disruption of vascular connectivity, and depletion of assimilates. How plants adapt their root systems to cope with different types of belowground biotic stresses is not well known. In this paper we compare above- and belowground plant adaptations to three nematode species with distinct tissue migration and feeding behaviours to study mechanisms underlying tolerance to different types of biotic stresses. We monitored both green canopy growth and changes in root system architecture of Arabidopsis inoculated with Pratylenchus penetrans, Heterodera schachtii, and Meloidogyne incognita. This revealed three distinct phases in aboveground plant responses: (i) initial growth inhibition associated with host invasion and tissue damage, (ii) persistent growth reduction associated with nematode sedentarism, and (iii) late growth stimulus in more advanced stages of infection. Specific adaptations in the root systems further revealed fundamentally different stress coping strategies. Tissue damage and intermittent feeding by P. penetrans in the root cortex did not induce significant changes in root system architecture. Tissue damage to the root cortex and prolonged feeding on host vascular cells by H. schachtii induced secondary root formation compensating for primary root growth inhibition. Prolonged feeding on host vascular cell by M. incognita alone did not induce secondary root formation, but was accompanied by typical local tissue swelling instead. Our data suggest that local secondary root formation and tissue swelling are two distinct compensatory mechanisms underlying tolerance to sedentarism by root-feeding nematodes. HighlightHow plants utilize root system plasticity to cope with different types of biotic stresses by root feeding nematodes remains largely unknown. Here, we report on specific adaptive growth responses in Arabidopsis roots to three nematode species, Pratylenchus penetrans, Heterodera schachtii, and Meloidogyne incognita, with fundamentally different strategies for host invasion, subsequent migration through host tissue, and feeding on host cells.

O_LIVolatile organic compounds (VOCs) emitted by soil bacteria influence interactions with other soil microbes and with plant roots. While their potential as plant-growth promoters is well recognized, their role in promoting plant resilience to abiotic stress and the underlying molecular mechanisms remains poorly understood. Here, we investigate the role of Pseudomonas VOCs in enhancing plant resilience to drought stress. C_LIO_LIArabidopsis thaliana plants were exposed to VOCs emitted by Pseudomonas strains under both control and osmotic-stress conditions. VOC exposure generally enhanced plant growth, and this effect was even more pronounced under both drought and salt stress. Transcriptomic analysis revealed that VOC exposure modulates key stress-responsive pathways, including those related to abscisic acid biosynthesis and signalling, sugar transport, iron uptake, aliphatic glucosinolate biosynthesis, and plant defences. Using Arabidopsis mutants, we identified abscisic acid and aliphatic glucosinolates as important components in mediating the plant response to VOCs. SWEET11/12 sugar transporters and ABA signaling genes were downregulated by VOCs exposure, in order to allow for a positive regulation of lateral root numbers (in case of SWEET genes) and plant growth in general under drought stress. In summary, using metabolomics, transcriptomics and functional analysis, we showed a negative cross-talk between the effects of VOCs on plant growth and glucosinolate production, whereas a positive interaction was observed between the biosynthesis of coumarins and VOCs. C_LIO_LINotably, VOCs also improved drought tolerance in soil-grown Brassica oleracea plants. We showed that VOC treatment altered the root-associated microbiome under drought, leading to a community composition more similar to that of well-watered plants. C_LIO_LIOur results show that Pseudomonas emitted VOCs can promote plant growth under drought conditions, linked to root transcriptional reprogramming and direct or indirect microbiome modulation. C_LI

O_LIResearch and rationale: This study investigates whether tissue-specific ethylene biosynthesis regulates stomatal conductance (gs) responses to changing [CO2] in Arabidopsis thaliana. While guard cells sense [CO2], mesophyll-derived signals are also implicated in stomatal control. We aimed to determine if ethylene production in guardcells or mesophyll is the primary driver of CO2-induced gs regulation. C_LIO_LIMethods: An acs octuple mutant with severely reduced ethylene production was complemented with tissue-specific ACS8/ACS11 transgenes driven by guard-cell, spongy-mesophyll, dual palisade/spongy-mesophyll, or whole-leaf promoters. Tissue-specific complementation in the different transgenic lines was confirmed and evaluated by qPCR, tissue-specific NEON expression, microscopic imaging, and ethylene production measurements. Gas-exchange measurements on intact plants recorded gs kinetics, CO2 assimilation, and water-use efficiency, across CO2 shifts. C_LIO_LIKey results: Guard-cell complementation nearly fully restored wild-type gs responses and reversed the mutants aberrant leaf phenotype. Spongy-mesophyll complementation failed to rescue either trait, while dual palisade- and spongy-mesophyll complementation yielded only partial recovery. C_LIO_LIConclusion: Ethylene produced in guard cells is the dominant regulator of CO2-induced stomatal conductance regulation, with mesophyll-derived ethylene contributing secondarily via long-distance signaling or by augmenting the overall ethylene pool. These findings underscore the importance of spatially regulated ethylene biosynthesis in balancing carbon assimilation and transpiration. C_LI

Root hair cells, which are instrumental in water and nutrient uptake, grow polarly from the epidermal cell layer of the root. Furthermore, plants growing in challenging climates and complex soil environments acclimatize their root hair phenotypes, either by altering root hair length or density. Toxic metal stress is one of the major environmental stresses faced by plant roots. In this study, we demonstrate that toxic metals, such as chromium and arsenite, increase root hair density as an adaptive response. Using the model plant Arabidopsis thaliana and other crops plants, like Zea mays and Triticum aestivum, we further discovered that increased root hair density is caused by shorter epidermal cell length rather than alteration of epidermal cell fate. This study highlights the adaptive cellular and anatomical features of roots during toxic metal stress in evolutionary diverse plant species.

O_LIRationale: Although trees encounter diverse fungal communities, it is unclear how they adjust their physiology in response to fungal ecological strategies before physical contact. We tested whether volatile organic compounds (VOCs) emitted by fungi are sufficient to induce systemic, lifestyle-consistent metabolic states in poplar roots and leaves. C_LIO_LIMethods: Populus x canescens roots were exposed to VOCs from a pathogen (Heterobasidion annosum), a saprotroph (Postia placenta) or an ectomycorrhizal mutualist (Laccaria bicolor) for six weeks in a contact-free pot-in-pot system. Untargeted LC-MS metabolomics characterized VOC-induced metabolic reprogramming in roots and leaves. C_LIO_LIKey results: Fungal VOC exposure alone reconfigured the metabolomes of roots and leaves, with strong discrimination between treatments despite belowground exposure. Poplar revealed a shared VOC-responsive component, but also fungus-specific programmes: pathogen VOCs produced a suppression-dominated systemic phenotype; saprotroph VOCs promoted lipid-centred metabolic activation; and mutualist VOCs elicited restrained, compatibility-consistent shifts with targeted pathway modulation. C_LIO_LIMain conclusion: Volatile-mediated surveillance allows trees to anticipate fungal lifestyle-associated cues and adjust systemic metabolism before physical contact occurs. This links airborne fungal cues to whole-plant physiological configuration and extends plant-fungal recognition beyond contact-dependent mechanisms. C_LI One-sentence summaryVolatile-mediated surveillance allows trees to anticipate fungal lifestyle and adjust systemic metabolism before physical contact occurs.

Phosphate (Pi) and phosphite (Phi), a non-metabolizable analogue of Pi, are taken up by plant roots through the same transport system. Whereas Pi is an essential nutrient for plants, Phi might function as a biostimulant and in protection against pathogens. However, how Phi mechanistically exerts beneficial effects on plants remains unsolved. We examined the impact of Phi and Pi on Arabidopsis thaliana and rice growth and upon pathogen infection. Phi inhibited the in vitro growth of Plectosphaerella cucumerina and Fusarium fujikuroi in a dose-dependent manner, whereas Magnaporthe oryzae growth was largely unaffected. Phis effect on plant growth was dependent on the plant species, the basal Pi level in the plant, and the ratio Pi to Phi. In Arabidopsis, Phi enhanced resistance to P. cucumerina by triggering a hypersensitive response-like cell death. Notably, Phi reversed Pi-induced susceptibility to blast (M. oryzae) and bakanae (F. fujikuroi) diseases in rice. Transcriptomic analysis revealed that Phi triggered extensive reprogramming in rice under high Pi, including the activation of signaling pathways enriched in phosphorylation-dependent processes, while attenuating induction of carbon metabolism. Phi acts as a multifaceted agent, promotes balanced metabolic state, improved plant performance, and reduced Pi-induced disease susceptibility when applied under appropriate Pi conditions. HighlightPhosphite application confers protection against fungal pathogens in Arabidopsis and rice plants by regulating signaling pathways depending on phosphorylation processes.

Under climate change, understanding how plants and crops respond to drought is essential for basic research in ecology and evolution, and improving agricultural resilience. One common method of simulating drought in experimental conditions is by applying polyethylene glycol (PEG) to plants. We investigated drought growth responses in Medicago lupulina (black medic) using PEG to simulate drought stress. We grew Medicago lupulina plants inoculated with Sinorhizobium meliloti in Magenta boxes under controlled conditions and randomly assigned them to one of three treatments: a control, PEG applied to the bottom (PEG added to the bottom-watering container of a magenta box), or PEG applied from the top (PEG poured over the growth media). After 60 days, we measured true leaf number, nodule count, and below- and above-ground dry biomass. PEG treatments significantly reduced above-ground growth, including total biomass and leaf number, but unexpectedly increased nodulation. Our results suggest that while PEG effectively simulates drought stress on above-ground growth parameters, it may not accurately simulate drought effects on rhizobial symbiosis. PEG treatments had no effect on below-ground biomass, suggesting that increased nodulation is not a result of increased plant investment in below-ground growth under simulated drought. We hypothesize that PEG, as a persistent liquid that plants do not absorb, created conditions favorable for nodulation. Overall, these results highlight the importance of interpreting PEG-simulated drought experiments with caution when assessing mutualistic interactions.

C4 photosynthesis is a CO2-concentration mechanism that separates CO2 fixation between two cell types, thereby reducing photorespiration and making C4 plants more efficient than their C3 counterparts. While the C4 cycle has evolved multiple times across different genera, this study evaluates very closely related C3 and C4 species within the genus Flaveria. Apart from their carbon metabolism, C4 plants also possess adaptations in their mineral nutrition. One key nutrient which is also directly involved in photosynthesis is phosphorus. It is absorbed by the plant in the form of inorganic phosphate and is an essential component of DNA, ATP, lipids, and carbohydrates. In the Flaveria C4 species, but not in the C3 species, phosphate limitation was shown to affect the dark reactions of photosynthesis. This study investigates how phosphate deficiency impacts the light reactions in C3 and C4 Flaveria plants. We observed a differential response in the functionality of photosynthetic energy conversion between the two species. When exposed to a limited phosphate supply, the C3 species reduced its linear electron transport rate while dissipating excess energy through high-energy quenching, which was regulated by a higher pH gradient across the thylakoid membrane. In contrast, the C4 species did not regulate its photosynthetic light reaction under phosphate limitation. Instead, it exhibited increased stress levels, evidenced by a stronger biomass reduction and the induction of stress markers in the leaves. Additionally, this study uncovered an acceleration in NPQ relaxation during phosphate limitation, regardless of the photosynthesis type. HighlightPhosphate deficiency reduced linear electron transport rates and induced dissipation of excess energy through non-photochemical quenching in the C3 Flaveria species, while in the C4 species, despite elevated stress levels, the photosynthetic light reactions were unaffected.