Jing-Quan Yu

Reactive oxygen species are involved in brassinosteroid-induced stress tolerance in cucumber.

Brassinosteroids (BRs) induce plant tolerance to a wide spectrum of stresses. To study how BR induces stress tolerance, we manipulated the BR levels in cucumber (Cucumis sativus) through a chemical genetics approach and found that BR levels were positively correlated with the tolerance to photo-oxidative and cold stresses and resistance to Cucumber mosaic virus. We also showed that BR treatment enhanced NADPH oxidase activity and elevated H2O2 levels in apoplast. H2O2 levels were elevated as early as 3 h and returned to basal levels 3 d after BR treatment. BR-induced H2O2 accumulation was accompanied by increased tolerance to oxidative stress. Inhibition of NADPH oxidase and chemical scavenging of H2O2 reduced BR-induced oxidative and cold tolerance and defense gene expression. BR treatment induced expression of both regulatory genes, such as RBOH, MAPK1, and MAPK3, and genes involved in defense and antioxidant responses. These results strongly suggest that elevated H2O2 levels resulting from enhanced NADPH oxidase activity are involved in the BR-induced stress tolerance.

Functional Analysis of the Arabidopsis PAL Gene Family in Plant Growth, Development, and Response to Environmental Stress

Phenylalanine ammonia-lyase (PAL) catalyzes the first step of the phenylpropanoid pathway, which produces precursors to a variety of important secondary metabolites. Arabidopsis (Arabidopsis thaliana) contains four PAL genes (PAL1–PAL4), but there has been no genetic analysis to assess the biological functions of the entire gene family. Here, we report the generation and analysis of combined mutations for the four Arabidopsis PAL genes. Contrary to a previous report, we found that three independent pal1 pal2 double mutants were fertile and generated yellow seeds due to the lack of condensed tannin pigments in the seed coat. The pal1 pal2 double mutants were also deficient in anthocyanin pigments in various plant tissues, which accumulate in wild-type plants under stress conditions. Thus, PAL1 and PAL2 have a redundant role in flavonoid biosynthesis. Furthermore, the pal1 pal2 double mutants were more sensitive to ultraviolet-B light but more tolerant to drought than wild-type plants. We have also generated two independent pal1 pal2 pal3 pal4 quadruple knockout mutants, which are stunted and sterile. The quadruple knockout mutants still contained about 10% of the wild-type PAL activity, which might result from one or more leaky pal mutant genes or from other unknown PAL genes. The quadruple mutants also accumulated substantially reduced levels of salicylic acid and displayed increased susceptibility to a virulent strain of the bacterial pathogen Pseudomonas syringae. These results provide further evidence for both distinct and overlapping roles of the Arabidopsis PAL genes in plant growth, development, and responses to environmental stresses.

Effects of root exudates and aqueous root extracts of cucumber (Cucumis sativus) and allelochemicals, on photosynthesis and antioxidant enzymes in cucumber

Abstract The effects of root exudates and aqueous root extracts of cucumber ( Cucumis sativus ) and allelochemicals on root antioxidant enzymes and leaf photosynthesis, transpiration and stomatal conductance were investigated in cucumber. Cucumber seedlings were incubated in solutions containing root exudates at 50 or 100 mg/l, root extracts at 1:100, 1:50, 1:25 and 1:10 (root dry weight:distilled water), and derivatives of benzoic and cinnamic acids at 0.25 mM, respectively. Root peroxidase and superoxide dismutase activities increased significantly after exposure to allelopathic agents. Membrane peroxidation was also enhanced by root exudates, root extracts and some of the tested acids. Allelopathic agents reduced leaf stomatal conductance from 1.28 mol m −2 s −1 to 0.02–0.33 mol m −2 s −1 . Leaf transpiration was reduced by 67% by root exudates at 100 mg/l, by 85–95% by root extracts, and by 51–87% by tested acids, respectively. Net assimilate rate was also inhibited by 29% by root exudates at 100 mg/l, by 49–83% by root extracts, and by 7–43% by tested acids, respectively. The intercellular CO 2 concentrations for the treated seedlings were only 47–89% of the control. However, leaf temperature was increased by 2–4°C by the tested agents.

Effects of Root Exudates of Cucumber (Cucumis sativus) and Allelochemicals on Ion Uptake by Cucumber Seedlings

AbstractThe effects of root exudates of cucumber, aromatic carboxylic acids in root exudates, and their analogs upon the uptake of NO3,

Phytotoxic substances in root exudates of cucumber (Cucumis sativus L.)

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Role of brassinosteroids in alleviation of phenanthrene–cadmium co-contamination-induced photosynthetic inhibition and oxidative stress in tomato

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