Xiao Zhang

Abstract One of the most important functions of the plant hormone abscisic acid (ABA) is to induce stomatal closure by reducing the turgor of guard cells under water deficit. Under environmental stresses, hydrogen peroxide (H2O2), an active oxygen species, is widely generated in many biological systems. Here, using an epidermal strip bioassay and laser-scanning confocal microscopy, we provide evidence that H2O2 may function as an intermediate in ABA signaling in Vicia faba guard cells. H2O2 inhibited induced closure of stomata, and this effect was reversed by ascorbic acid at concentrations lower than 10−5 m. Further, ABA-induced stomatal closure also was abolished partly by addition of exogenous catalase (CAT) and diphenylene iodonium (DPI), which are an H2O2 scavenger and an NADPH oxidase inhibitor, respectively. Time course experiments of single-cell assays based on the fluorescent probe dichlorofluorescein showed that the generation of H2O2 was dependent on ABA concentration and an increase in the fluorescence intensity of the chloroplast occurred significantly earlier than within the other regions of guard cells. The ABA-induced change in fluorescence intensity in guard cells was abolished by the application of CAT and DPI. In addition, ABA microinjected into guard cells markedly induced H2O2 production, which preceded stomatal closure. These effects were abolished by CAT or DPI micro-injection. Our results suggest that guard cells treated with ABA may close the stomata via a pathway with H2O2 production involved, and H2O2 may be an intermediate in ABA signaling.

Abstract A number of phosphate (Pi) starvation- or mycorrhiza-regulated Pi transporters belonging to the Pht1 family have been functionally characterized in several plant species, whereas functions of the Pi transporters that are not regulated by changes in Pi supply are lacking. In this study, we show that rice (Oryza sativa) Pht1;1 (OsPT1), one of the 13 Pht1 Pi transporters in rice, was expressed abundantly and constitutively in various cell types of both roots and shoots. OsPT1 was able to complement the proton-coupled Pi transporter activities in a yeast mutant defective in Pi uptake. Transgenic plants of OsPT1 overexpression lines and RNA interference knockdown lines contained significantly higher and lower phosphorus concentrations, respectively, compared with the wild-type control in Pi-sufficient shoots. These responses of the transgenic plants to Pi supply were further confirmed by the changes in depolarization of root cell membrane potential, root hair occurrence, 33P uptake rate and transportation, as well as phosphorus accumulation in young leaves at Pi-sufficient levels. Furthermore, OsPT1 expression was strongly enhanced by the mutation of Phosphate Overaccumulator2 (OsPHO2) but not by Phosphate Starvation Response2, indicating that OsPT1 is involved in the OsPHO2-regulated Pi pathway. These results indicate that OsPT1 is a key member of the Pht1 family involved in Pi uptake and translocation in rice under Pi-replete conditions.

Inorganic phosphorus (Pi) is an essential element in numerous metabolic reactions and signaling pathways, but the molecular details of these pathways remain largely unknown. In this study, metabolite profiles of maize (Zea mays L.) leaves and roots were compared between six low-Pi-sensitive lines and six low-Pi-tolerant lines under Pi-sufficient and Pi-deficient conditions to identify pathways and genes associated with the low-Pi stress response. Results showed that under Pi deprivation the concentrations of nucleic acids, organic acids and sugars were increased, but that the concentrations of phosphorylated metabolites, certain amino acids, lipid metabolites and nitrogenous compounds were decreased. The levels of secondary metabolites involved in plant immune reactions, including benzoxazinoids and flavonoids, were significantly different in plants grown under Pi-deficient conditions. Among them, the 11 most stable metabolites showed significant differences under low- and normal-Pi conditions based on the coefficient of variation (CV). Isoleucine and alanine were the most stable metabolites for the identification of Pi-sensitive and Pi-resistant maize inbred lines. With the significant correlation between morphological traits and metabolites, five low-Pi-responding consensus genes associated with morphological traits and simultaneously involved in metabolic pathways were mined by combining metabolites profiles and genome-wide association study (GWAS). The consensus genes induced by Pi deficiency in maize seedlings were also validated by reverse-transcription quantitative polymerase chain reaction (RT-qPCR). Moreover, these genes were further validated in a recombinant inbred line (RIL) population, in which the glucose-6-phosphate-1-epimerase encoding gene mediated yield and correlated traits to phosphorus availability. Together, our results provide a framework for understanding the metabolic processes underlying Pi-deficient responses and give multiple insights into improving the efficiency of Pi use in maize.