Physiologia plantarum最新文献

Plant sphingolipids are lipophilic membrane components essential for different cellular functions but they also act as signaling molecules in various aspects of plant development. However, the interaction between plant sphingolipids and abscission remains largely uncharacterized. Here, the possible role of sphingolipids in regulating fruit abscission was examined in the abscission zone (AZ) of olive fruit. To this end, sphingolipid levels were manipulated through the application of exogenous sphingolipid long-chain bases (LCBs) or biosynthesis inhibitors, and their effects on fruit abscission as well as sphingolipid LCB/gene expression, hormones, reactive oxygen species (ROS) and cell death levels were examined in the AZ of olive fruit. Our data indicated that exogenous sphinganine (d18:0) induced fruit abscission, whereas the application of sphingosine (d18:1) or phytosphingosine (t18:0) or their phosphorylated derivatives did not have an effect on fruit abscission. Moreover, inhibition of LCB kinase or ceramide synthase, which increases sphingolipid LCB levels in the AZ, reduced fruit break strength. This induction of fruit abscission is associated with elevated ROS levels and cell death in the AZ enriched in salicylic acid (SA) and jasmonic acid (JA). Along the same line, programmed cell death (PCD) was particularly evident on the distal side of the AZ. These data suggest that endogenous d18:0 plays a key cellular role as signaling molecule functioning upstream of the SA/JA signaling pathway in mediating PCD spatially regulated in the AZ during fruit abscission. Overall, the findings reported here provide insight into the complex connection between PCD and plant sphingolipid LCBs, uncovering their interaction in the abscission process.

Water is the basic molecule in living beings, and it has a major impact on vital processes. Plants are sessile organisms with a sophisticated regulatory network that regulates how resources are distributed between developmental and adaptation processes. Drought-stressed plants can change their survival strategies to adapt to this unfavorable situation. Indeed, plants modify, change, and modulate gene expression when grown in a low-water environment. This adaptation occurs through several mechanisms that affect the expression of genes, allowing these plants to resist in dry regions. Epigenetic modulation has emerged as a major factor in the transcription regulation of drought stress-related genes. Moreover, specific molecular and epigenetic modifications in the expression of certain genetic networks lead to adapted responses that aid a plant's acclimatization and survival during repeated stress. Indeed, understanding plant responses to severe environmental stresses, including drought, is critical for biotechnological applications. Here, we first focused on drought stress in plants and their general adaptation mechanisms to this stress. We also discussed plant epigenetic regulation when exposed to water stress and how this adaptation can be passed down through generations.

A common assumption of plant hydraulic physiology is that high hydraulic efficiency must come at the cost of hydraulic safety, generating a trade-off that raises doubts about the possibility of selecting both productive and drought-tolerant herbaceous crops. Wetland plants typically display high productivity, which requires high hydraulic efficiency to sustain transpiration rates coupled to CO₂ uptake. Previous studies have suggested high vulnerability to xylem embolism of different wetland plants, in line with expected trade-offs. However, some hygrophytes like Cyperus alternifolius L. can also experience prolonged periods of low water levels leading to substantial drought stress. We conducted an in-depth investigation of this species' hydraulic safety and efficiency by combining gas exchange measurements, hydraulic measurements of leaf hydraulic efficiency and safety, optical measurements of xylem vulnerability to embolism, and determination of cell turgor changes under drought. Our data confirm the high hydraulic efficiency of this wetland species, but at the same time, reveal its surprising drought tolerance in terms of turgor loss point and critical water potential values inducing xylem embolism and hydraulic failure, which were well below values inducing turgor loss and full stomatal closure. C. alternifolius emerges as a highly productive plant that is also well-equipped to tolerate drought via a combination of early stomatal closure and delayed onset of hydraulic damage. The species might represent a model plant to develop crops combining two of the most desirable traits in cultivated plants, i.e., high yield and significant drought tolerance.

Melatonin (MLT) is an indole derivative that exhibits hormone-like activities in plants, regulating multiple aspects of growth and development. Due to its role in mitigating oxidative stress and facilitating osmoprotectant accumulation, MLT enhances abiotic stress tolerance, although the pathways and metabolic mechanisms involved remain unclear despite being studied in various crops. This work aimed to investigate the changes elicited by the exogenous MLT application at different concentrations (10, 50, 150 μM) and its role in mitigating the salinity stress in Lactuca sativa L. through metabolomics and phenotyping approaches. Our results clearly indicated that MLT increases photosynthetic efficiency at high dosage (150 μM) at either early or late salinity stress conditions (p < 0.01). Untargeted metabolomics provided insight into the significant effect of salinity and MLT (p < 0.01 in both cases, according to multivariate chemometrics), mediated by a broad reprogramming involving secondary metabolism, phytohormones, fatty acids and amino acids biosynthesis. In detail, 150 μM MLT induced an adjustment of the phytohormones profile to reduce the salinity-induced damages. Our findings support the well-known potential of melatonin in alleviating salinity stress. These findings address existing challenges in studying the molecular effects of MLT in mitigating abiotic stress, providing insights into the biochemical pathways that drive its effectiveness. In this sense, further research is acknowledged to provide a multidisciplinary high throughput perspective leading to its exploitation in a wide range of crops of agricultural and economic importance.

Heavy metal pollution, especially arsenic toxicity, significantly impairs plant growth and development. Phenolic acids, known for their antioxidant properties and involvement in stress signaling, are gaining increased attention as plant secondary metabolites with the potential to enhance plant resistance to these stressors. This study aimed to investigate the effects of different concentrations of syringic acid (SA1, 10 μM; SA2, 250 μM; SA3, 500 μM) on growth, photosynthetic parameters, and antioxidant activity in lettuce seedlings subjected to arsenic stress (As, 100 μM). Arsenic stress reduced growth by 56.7%, water content by 7.39%, and osmotic potential by 26.2% in lettuce leaves compared to control. Conversely, SA1 and SA2 treatments mitigated the adverse effects of arsenic on growth and preserved the water balance in plants. However, the SA3 treatment led to a decrease in growth by 18.9% and 39.5% in the SA3 and As+SA3 groups, respectively, indicating that high-dose SA treatment adversely affected lettuce leaves under both control and stress conditions. Exogenous SA1 treatment significantly improved photosynthesis, whereas SA2 provided milder benefits and SA3 did not reduce the adverse effects of arsenic exposure. Arsenic stress increased H₂O₂ content by 47.3% and lipid peroxidation by 33.4% in lettuce seedlings. SA1 treatment effectively reduced oxidative stress by enhancing the activities of key antioxidant enzymes, such as superoxide dismutase (SOD) and peroxidase (POX). Moreover, SA1 was successful in maintaining the glutathione (GSH) pool, whereas SA2 primarily promoted ascorbate (AsA) regeneration. In conclusion, 10 μM of syringic acid (SA1) was identified as the optimal dose for reducing arsenic stress in lettuce by enhancing antioxidant activity and supporting growth. Overall, the findings underscore the potential of SA1 treatment in enhancing the resilience of lettuce to heavy metal toxicity.

Diatoms dominate phytoplankton communities in turbulent waters, where light fluctuations can be frequent and intense. Due to this complex environment, these heterokont microalgae display remarkable photoprotection strategies, including a fast Non-Photochemical Quenching (NPQ). However, in nature, several abiotic parameters (such as temperature) can influence the response of photosynthetic organisms to light stress in a synergistic or antagonistic manner. Yet, the combined effects of light and these other drivers on the photosynthetic and photoprotective capacity of diatoms are still poorly understood. In this work, we investigated the impact of short-term temperature and light stress on the model diatom Phaeodactylum tricornutum, combining NPQ induction-recovery assays or light curves with a broad gradient of superimposed temperature treatments (5 to 35°C). We employed mutant lines deficient in NPQ generation (vde KO) or recovery (zep3 KO) and wild type. We found that temperature and light have a synergistic effect: lower temperatures limited both the photosynthetic capacity and NPQ, while the general photophysiological performance was enhanced with warming, up to a heat-stress limit (above 30°C). We discuss the temperature effects on NPQ induction and recovery and propose that these are independent from the energy requirements of the cells and result from altered xanthophyll cycle dynamics. Namely, we found that de-epoxidation activity strongly increases with temperature, outweighing epoxidation and resulting in a positive increase of NPQ with temperature. Finally, we propose that in a short-term time frame, temperature and light have a synergistic and not antagonistic effect, with a positive relationship between increasing temperature and NPQ.

Photosynthesis, electron transport to carbon assimilation, photorespiration and alternative electron transport, light absorption of the two photosystems, antioxidative protection and pigment contents were investigated in S. alpina leaves. S. alpina is an alpine snow-bed plant which can be found with green leaves after snowmelt. At least 24% of the leaves were formed at the beginning of the vegetation period in the previous year and survived two consecutive vegetation periods under contrasting environmental conditions. In leaves still covered by snow (SNOW), the parameters of antioxidative protection and carbon assimilation were lower than in leaves from the previous vegetation period (NEW) or several weeks after snowmelt (OLD). Directly after snowmelt, antioxidative protection was strongly but transitionally increased. The senescence of leaves did not depend on antioxidative scavenging capacity. Lower carbon assimilation was not related to increases in alternative electron flow (ETR_alt) in SNOW leaves. In the second vegetation period, light absorption by PSII decreases in favour of PSI in OLD leaves. This allows OLD leaves to keep the electron transport chain more oxidised and to support photorespiration with increased ATP synthesis by cyclic electron transport around PSI. This study describes how the leaves of a unique plant can cope with contrasting environmental conditions.

Plant carotenoids are plastid-synthesized isoprenoids with roles as photoprotectants, pigments, and precursors of bioactive molecules such as the hormone abscisic acid (ABA). The first step of the carotenoid biosynthesis pathway is the production of phytoene from geranylgeranyl diphosphate (GGPP), catalyzed by phytoene synthase (PSY). GGPP produced by plastidial GGPP synthases (GGPPS) is channeled to the carotenoid pathway by direct interaction of GGPPS and PSY enzymes. Three plastid-localized GGPPS isoforms (referred to as SlG1-3) and three PSY enzymes (PSY1-3) are present in tomato (Solanum lycopersicum). Our previous work showed that SlG1 and PSY3 function together in the roots, whereas the rest of the isoforms are required in aerial tissues. Here we generated and analyzed combinations of double mutants lacking PSY1 or PSY2 and SlG2 or SlG3 to investigate the contribution of specific GGPPS and PSY pairs to the production of carotenoids and ABA in different tissues of the tomato plant. Despite that the loss of individual enzymes was found to trigger compensatory mechanisms that complicate interpretation of the results, the results confirm a major role for SlG3 in providing GGPP to PSY2 for housekeeping carotenoid biosynthesis in leaves, whereas SlG2 and PSY1 become most relevant when a more active production is required in flowers and breaker fruits, i.e., at the onset of ripening. We could also confirm that ABA production in the fruit pericarp is more dependent on PSY1 activity than on total carotenoid levels and that fruit size correlates with ABA levels accumulated in ripe rather than breaker fruits.

Glycolate oxidase (GOX) is a crucial enzyme of photorespiration involving carbon metabolism and stress responses. It is poorly understood, however, how its activities are modulated in response to oxidative stress elicited by various environmental cues. Analysis of Arabidopsis catalase-defective mutant cat2 revealed that the GOX activities were gradually repressed during the growth, which were accompanied by decreased salicylic acid (SA)-dependent cell death, suggesting photorespiratory H₂O₂ may entrain negative feedback regulation of GOX in an age-dependent manner. Intriguingly, a loss-of-function mutation in GLYCOLATE OXIDASE1 (GOX1) rather than in GOX2 and GOX3 attenuated the SA responses of cat2. We found that GOX1 is S-nitrosylated at Cys-343 during consecutive oxidative stress in the cat2 mutant. Subsequently, increased GOX1-SNO formations may contribute to progressively decreased GOX activities and then compromised photorespiratory H₂O₂ flux, which forms a negative feedback loop limiting the amplified activation of SA-dependent defence responses. Together, the data reveal that GOX S-nitrosylation is involved in the crosstalk between photorespiratory H₂O₂ and NO signalling in the fine-tuning regulation of oxidative stress responses and further highlight that NO-based S-nitrosylation acts as an on-off switch for ROS homeostasis.

Cytochrome P450s of the CYP79 family catalyze two N-hydroxylation reactions, converting a selected number of amino acids into the corresponding oximes. The sorghum genome (Sorghum bicolor) harbours nine CYP79A encoding genes, and here sequence comparisons of the CYP79As along with their substrate recognition sites (SRSs) are provided. The substrate specificity of previously uncharacterized CYP79As was investigated by transient expression in Nicotiana benthamiana and subsequent transformation of the oximes formed into the corresponding stable oxime glucosides catalyzed by endogenous UDPG-glucosyltransferases (UGTs). CYP79A61 uses phenylalanine as a substrate, whereas CYP79A91, CYP79A93, and CYP79A95 use valine and isoleucine as substrates, with CYP79A93 showing the ability also to use phenylalanine. CYP79A94 uses isoleucine as a substrate. Analysis of 249 sorghum transcriptomes from two different sorghum cultivars showed the expression levels and tissue-specific expression of the CYP79As. CYP79A1 is the committed gene in dhurrin formation and was the highest expressed gene in most tissues/organs. CYP79A61 was primarily expressed in fully developed leaf blades and leaf sheaths. CYP79A91 and CYP79A92 were expressed mainly in roots >200 cm below ground, while CYP79A93 and CYP79A94 were most highly expressed in the leaf collar and leaf sheath, respectively. The possible signalling effects of the oximes and their metabolites produced in different sorghum tissues are discussed.