Photoinhibition is the popular topic in plant photosynthesis. However, restricted to experimental systems of in vitro membranes, knowledge of photosystem II (PSII) donor-side photoinhibition remains limited. Here, we report the first in vivo study of the mechanism in the marine higher plant Zostera marina. Preferential oxygen-evolving complex photoinactivation decreased the light-harvesting capacity and enhanced photosystem I cyclic electron flow (CEF). Non-photochemical quenching was inefficient and alternative electron flows, e.g. chlororespiration, Mehler reaction, malic acid synthesis, and photorespiration, remained unactivated, thereby reducing the unnecessary consumption of limited electron resources and maintaining a well carbon assimilation level. At variance with the PSII acceptor-side photoinhibition, the PSII photodamage of Z. marina was not attributed to 1O2 but was associated with the long-lived P680+ resulted from the photoinactivated OEC. Furthermore, we provided the novel insights into the PSII donor-side photoinhibition that rare PSII-CEF and ascorbate assumed photoprotective roles in Z. marina, which could donate electrons to the PSII reaction center to prevent the oxidative damage by P680+. This study addressed an important knowledge gap in PSII donor-side photoinhibition, providing a novel understanding of photosynthetic regulation mechanism responding to light stress.

The costs of Biscutella laevigata adaptation, a facultative metallophyte, to an environment polluted with heavy metals were established by analyzing the differences in embryological processes between plants from two populations in Southern Poland (a mountain, in the Tatra Mountains and calamine, in Bolesław). Disturbances in male and female lineage development and degeneration processes occurred in the anthers and ovules of plants from both populations, but with a higher frequency in the calamine population where A part of stamens/anthers and ovules in flowers were in a stage of degenertion. which could be interpreted as a strategy to save resources limited by the environment. The distribution of high-esterified homogalacturonan detected by LM20 antibody in the cell walls of embryos from the calamine population could be part of a resistance/defense system. The results from both populations indicate that B. laevigata has already developed adaptation/tolerance, enabling maintenance of the calamine population over time. Tolerant species could be an important source for revitalization and/or phytoremediation of polluted environments.

Rice is one of the most susceptible plant to iron (Fe) deficiency under neutral and alkaline conditions. Alkaline stress induces H2O2 production and increases the deposition of Fe on roots surface, which causes leaf chlorosis and Fe deficiency in rice. Gene chip and qRT-PCR analysis indicated that the expression of nitrate reductase (NR) genes were down-regulated by alkaline treatment, which resulted in significantly decreased nitrate activities and nitric oxide (NO) production in epidermis and stele, where the H2O2 was accumulated. In contrast, treatment with sodium nitroprusside (SNP), a NO donor, strongly alleviates alkaline-induced Fe deficiency by limiting Fe plaque formation. Increasing the NO signal significantly reduces the accumulation of H2O2 and lignin barrier, but enhances phenolic acid secretion in root epidermis and stele under alkaline stress. The secreted phenolic acid effectively mobilized the apoplast Fe and increased Fe uptake in root, thus which alleviate the Fe deficiency response and down-regulate expression of Fe uptake genes under alkaline condition. In conclusion, alkaline stress inhibits the NR activity and NO production in roots of rice, which plays a vital role in mobilizing the apoplast Fe by regulation of H2O2 and phenolic acids concentrations.

Photoperiod and circadian controls play crucial roles in the regulation of chloroplast biogenesis. To understand more about the regulation of this process, we compared the greening of the first leaves of wild type barley and two WHIRLY1 (WHY1)-deficient lines. Seedlings were grown in darkness for 4 days prior and then exposed to light at the beginning of the photoperiod on the 5th day or under standard photoperiod conditions. The accumulation of chlorophyll, as well plastid-encoded photosynthetic transcripts and proteins was delayed in the WHY1-deficient lines under standard photoperiod conditions because of defects in plastid gene expression, ribosomal processing and photosynthetic protein accumulation. The acquisition of full photosynthetic capacity was delayed by about 11 days in the first leaves and the newly forming leaves of the WHY1-deficient lines compared to the wild type. However, the light-dependent accumulation of pigments, transcripts and photosynthetic proteins was similar in all lines when etiolated seedlings were exposed to light. These results demonstrate that WHY1 is required for the integration of photoperiod-dependent signalling and chloroplast development in barley leaves.

Clonal selection and vegetative propagation determine low genetic variability in grapevine cultivars, although it is common to observe diverse phenotypes. Environmental signals may induce epigenetic changes altering gene expression and phenotype. The range of phenotypes that a genotype expresses in different environments is known as phenotypic plasticity. DNA methylation is the most studied epigenetic mechanism, but only few works evaluated this novel source of variability in grapevines. In the present study, we analyzed the effects on phenotypic traits and epigenome of three Vitis vinifera cv. Malbec clones cultivated in two contrasting vineyards of Mendoza, Argentina. Anonymous genome regions were analyzed using Methylation-Sensitive Amplified Polymorphism (MSAP) markers. Clone-dependent phenotypic and epigenetic variability between vineyards were found. The clone that presented the clearer MSAP differentiation between vineyards was selected and analyzed through Reduced Representation Bisulfite Sequencing. Twenty-nine differentially methylated regions (DMRs) between vineyards were identified and associated to genes and/or promoters. We discuss about a group of genes related to hormones homeostasis and sensing that could provide a hint of the epigenetic role in the determination of the different phenotypes observed between vineyards and conclude that DNA methylation has an important role in the phenotypic plasticity and that epigenetic modulation is clone-dependent.

Phosphorus (P) deficiency is a major problem in agriculture, thus identifying factors affecting plant’s ability to reutilize previously assimilated P is a prerequisite for improving the P homeostasis in crops grown with P deficient soil. Here, we report the involvement of a NAC (No apical meristem [NAM], Arabidopsis transcription activation factor [ATAF] and Cup-shaped cotyledon [CUC]) transcription factor in P deficiency resistance in Arabidopsis. Compared to the wild type (WT, Col-0) plants, the anac044 mutant displayed P deficiency resistant phenotype, together with the increasing root length, root and shoot biomass under P deficiency. ANAC044 was frequently expressed, including roots and shoots. Upon P deficient treatment even within 1 d, ANAC044 transcript accumulation was strongly up-regulated. Further analysis revealed that, under P-deficient condition, the cell wall, particularly the pectin of anac044, released more P than that of WT, accompanied by an increment of ethylene production, as a result, more soluble P was available in anac044 root and shoot. Thus, the study here uncovers the role of ANAC044 in maintenance of P homeostasis through ethylene signaling.

Global warming is already affecting plant phenology, growth and reproduction. A wide range of evidence indicates warming effects on reproductive and vegetative traits, as well as phenology, but seldom do studies assess these traits in concert and across the whole of a plant's life cycle, particularly in wild species. Further, while there is evidence that these effects vary between species little is known about the extent of within-species variation for plant persistence under future warming scenarios. We assessed trait variation in response to warming in Oreomyrrhis eriopoda, an Australian native montane herb, in which within-species variation in germination strategy and growth characteristics has been demonstrated. We quantified associations between developmental trajectories and population-level variation in germination timing and examined whether the next-generation traits are altered by maternal growth conditions. Warming effects were expressed in different traits during different developmental stages. The effect of warming varied as a function of germination strategy, but germination strategy itself was conserved across generations. Thus, we conclude that understand the response of wild species to warming takes a whole-of-life perspective and attention to ecologically significant patterns of within species variation.

Nitrogen use efficiency (NUE) is an important and complex crops trait and its improvement represents a strategy to maintain high yield reducing N-supply. We report the genome-wide transcriptomic analysis of four eggplants contrasting for NUE to identify key genes related to the NUE pathway, after short- and long-term low-N exposure, in both root and shoot. Co-expression Gene Networks (CGN) analysis permitted to identify up-regulated differential expressed genes (DEGs) involved in the light reaction pathway, the biological processes response to inorganic substance, abiotic stimulus and cellular response to nitrogen starvation in high NUE genotypes. Some transcription factor (TF) were up-regulated in the N-use efficient genotypes, in particular, WRKY33 showed a significant up-regulation triggering the higher expression of 21 genes cluster including other TFs, many of which associated to N-metabolism. To validate our results, an independent de novo experiment including two other NUE-contrasting genotypes, at both low and high N supply, was carried out. Interestingly, the high significant WRKY33 expression and its cluster were confirmed in the high NUE genotypes at low-N supply. Moreover, the WRKY33 role was confirmed in Arabidopsis as the 35S::AtWRKY33 over expressing line showed a more competitive root system able to uptake more efficiently N from the soil.

In this study the cucumber and wheat plants were used to clarify the mechanism of redroot pigweed’s allelopathic effects on photosynthesis. In order to reach that goal, plants were cultivated hydroponically, treated by redroot pigweed’s leachate and finally chlorophyll fluorescence and photosynthetic gas exchange parameters, photosynthetic pigments content and the expression of photosynthetic genes (PsbA and PsbS) and allelochemical interaction with proteins of studied genes were analyzed. After exposure to the allelopathic stress, significant differences in the majority of photosynthetic characteristic were observed in the studied species. Redroot pigweed allelopathy led to alteration in photosynthesis performance, photochemistry, and photosynthetic genes expression of cucumber and wheat plants, ultimately its results were observed in morphological traits of plants. Molecular docking study strongly confirmed the possibility of direct binding and action of allelopathic compounds with allelopathic action’s target proteins. Overall, this study showed that compared to cucumber, the wheat plant is able to withstand the damaging effects of amaranth allelopathy on photosynthesis in order to resist and survive.

Diverse algae possess vegetative desiccation tolerance, the ability to recover from extreme desiccation without forming specialized resting structures. Green algal genera such as Tetradesmus (Sphaeropleales, Chlorophyceae) contain both terrestrial and aquatic species, providing an opportunity to compare physiological traits associated with the transition to land in closely related taxa. We subjected six species from aquatic and terrestrial habitats to three desiccation treatments varying in final relative humidity followed by short- and mid-term rehydration. We tested the capacity of the algae to recover from desiccation using the effective quantum yield of photosystem II as a proxy for physiological activity. The degree of recovery was dependent both on the habitat of origin and the desiccation scenario, with terrestrial, but not aquatic species, recovering from desiccation. Distinct strains of each species responded similarly to desiccation and rehydration, with the exception of one aquatic strain that recovered from the mildest desiccation. Cell ultrastructure was uniformly maintained in both aquatic and desert species during dehydration and rehydration, but staining with an amphiphilic styryl dye indicated desiccation-induced damage to the plasma membrane in the aquatic species. These analyses demonstrate that terrestrial Tetradesmus possess the vegetative desiccation tolerance phenotype, making these species ideal for comparative omics studies.

Arabidopsis Casparian strip membrane domain proteins (CASPs) form a transmembrane scaffold to recruit lignin biosynthetic enzymes for Casparian strip (CS) formation. Compared with Arabidopsis, rice root is more complex with a CS of the exodermis and sclerenchyma and a CS that does not block propidium iodide entry into the stele. Rice CASP1 is highly similar to AtCASPs, but it is not required for CS formation. Its mutation results in early leaf senescence and fewer tillers and does not change the CS structure and permeability. OsCASP1 is mainly located in the nuclear membrane. Its expression is concentrated in the root stele and at small lateral root tips and can be induced by salt stress. OsCASP1 mutation causes ectopic suberin deposition in small lateral roots and ion imbalances in the plant. Homeostatic disorder induces nutrient recycling and accelerate leaf senescence. To our knowledge, OsCASP1 is the first CASP to be described in the nuclear membrane; it modulates suberin deposition and does not involve CS formation, representing a novel regulatory mode of CASPs.

Yeast manganese (Mn) trafficking transporter for mitochondrial Mn-containing superoxide dismutase (MnSOD), yMTM1, belongs to mitochondrial carrier family (MCF) and is crucial for yeast MnSOD (ySOD2) activation. Arabidopsis AtMTM1 and AtMTM2 are homologs of yMTM1 and share conserved MCF motif sequence. We confirmed that AtMTM1 and AtMTM2 interacted with AtMnSOD (AtMSD1) in mitochondria and recovered ySOD2 activity in yMTM1-mutant cells. The redundant AtMTM1 and AtMTM2 have different gene expression patterns in tissues and methyl viologen (MV)-induced oxidative stress and also responded to most metal stresses along with AtMSD1. Bioassay revealed the contrasting root phenotype in microRNA-mediated AtMTM1 mutant (mtm1-i) and AtMTM2-null mutant (mtm2) under MV stress, and Mn supplement complemented the root lengths in single and mtm1-i mtm2-double mutants. We found decreased MnSOD activity was accompanied by increased FeSOD activity in double mutant. Transient expression of chloroplast-destined AtMSD1 highlighted that unidentified factors participated in AtMSD1 activation. Besides, the exogenous-expressed AtMSD1 activity was decreased in double mutant, and inductively coupled plasma optical emission spectrometry results showed that AtMTM1 and AtMTM2 involved in Mn and Fe homeostasis with a reciprocal regulation. Overall, AtMTM1 and AtMTM2 are important for MnSOD metalation and ion homeostasis, and their physiological regulations may stretch across mitochondria and chloroplasts.

Pistachio (Pistacia spp.) is a tree nut crop with relatively high salinity tolerance. Currently, limited information exists on its rootstock’s cellular responses to salinity stress, especially in its roots. In this study, we investigated salinity tolerance at cellular level, in two pistachio rootstocks, Pistacia integerrima (PGI) and a hybrid, P. atlantica x P. integerrima (UCB1). Root tip sections were categorized across a developmental gradient according to their xylem development, and their sodium content and suberin deposition were analyzed with fluorescence microscopy. Our data demonstrated a correlation between vacuolar sequestration of sodium ions (Na+) and salinity tolerance in the UCB1 genotype. In addition, UCB1 displayed higher basal levels of suberization in both the exodermis and endodermis that increased further after salinity stress. Notably, the root region immediately distal to the region of secondary xylem initiation showed the highest amount of vacuolar Na+ sequestration, indicating a developmental regulation of this process. Our cumulative data demonstrate that salinity tolerance in pistachio rootstock species is associated with both vacuolar Na+ sequestration and suberin deposition at apoplastic barriers, and both are correlated with a root developmental gradient. These cellular characteristics are phenotypes that can be screened during the selection for salinity tolerant woody plant species.

Mercury (Hg) is one of the most hazardous pollutants released by humans and is of global environmental concern. Mercury causes oxidative stress and strong cellular damages in plants, which can be attenuated by the biosynthesis of thiol-rich peptides (biothiols), which include glutathione (GSH) and phytochelatins (PCs). We analysed Hg tolerance and speciation in five Arabidopsis thaliana genotypes, the wild-type Col-0, three knockdown γ-glutamylcysteine synthetase (γECS) mutants and a knockout PC synthase (PCS) mutant. Mercury-PC complexes were detected in roots by HPLC-ESI-TOFMS, with its abundance being limited in γECS mutants. Analysis of Hg-biothiol complexes in the xylem sap revealed that HgPC2 occurs in wild-type Col-0 Arabidopsis, suggesting that Hg could be translocated associated with thiol-rich metabolites. Twenty genes involved in sulphur assimilation, GSH and PCs synthesis were differentially expressed in roots and shoots, implying a complex regulation, possibly involving post-translational mechanisms independent of GSH cellular levels. In summary, the present study describes the importance of biothiol metabolism and adequate GSH levels in Hg tolerance, and identifies for the first time Hg-PC complexes in the xylem sap. This finding supports that Hg-biothiol complexes could contribute to Hg mobilisation within plants.

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