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Abstract: Abscisic acid (ABA), H2O2 and nitric oxide (NO) are important signals in gene expression and physiological responses during plant adaptation to environmental stresses. The essential role of NR-derived NO production in ABA and H2O2 induced antioxidant enzymes were studied using transgenic tobacco plants over-expressing Stylosanthes guianensis 9-cis-epoxycartenoid dioxygenase gene (SgNCED1) for elevated ABA level, or over-expressing wheat oxalate oxidase gene (OxO) for elevated H2O2 level in comparison to the wild type. Compared to the wild type, higher levels of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and nitrate reductase (NR) activities and NO production were observed in all transgenic plants. For investigating the relationship of ABA, H2O2, and NR-produced NO in the induction of antioxidant enzyme activities, an inhibitor of ABA biosynthesis, scavengers of H2O2 and NO, and an inhibitor of NR were used in the experiments. The results indicate that H2O2-induced activities of SOD, CAT, and APX depends on NR-derived NO in OxO transgenic plants, while ABA-induced activities depends on H2O2 and NR-derived NO in SgNCED1 transgenic plants. Compared to unaltered nitrate reductase 2 (NIA2), NIA1 transcript was induced in both types of transgenic plants. It is suggested NR-derived NO is essential for ABA- or H2O2-induced antioxidant enzyme activities. [Copyright &y& Elsevier]

Abstract: Drought is a major limiting factor for turfgrass growth. Protection of triploid bermudagrass against drought stress by abscisic acid (ABA) and its association with hydrogen peroxide (H2O2) and nitric oxide (NO) were investigated. ABA treatment increased relative water content, decreased ion leakage and the percentage of dead plants significantly under drought stress. Superoxide dismutase (SOD) and catalase (CAT) activities increased in both ABA-treated and control plants, but more in ABA-treated plants, under drought stress. Malondialdehyde, an indicator of plant lipid peroxidation, was lower in ABA-treated plants than in control plants, indicating that ABA alleviated drought-induced oxidative injury. ABA treatment increased H2O2 and NO contents. ABA-induced SOD and CAT activities could be blocked by scavengers of H2O2 and NO, and inhibitors of H2O2 and NO generation. The results indicated that H2O2 and NO were essential for ABA-induced SOD and CAT activities. Both H2O2 and NO could induce SOD and CAT activities individually. SOD and CAT induced by H2O2 could be blocked by scavenger of NO and inhibitors of NO generation, while SOD and CAT induced by NO could not be blocked by scavenger of H2O2 and inhibitor of H2O2. The results revealed that ABA-induced SOD and CAT activities were mediated sequentially by H2O2 and NO, and NO acted downstream of H2O2. [Copyright &y& Elsevier]

Calmodulin-like proteins (CMLs) are unique Ca2+ sensors and play crucial roles in response to abiotic stress in plants. A salt-repressed PvCML9 from halophyte seashore paspalum (Paspalum vaginatum O. Swartz) was identified. PvCML9 was localized in the cytoplasm and nucleus and highly expressed in roots and stems. Overexpression of PvCML9 led to reduced salt tolerance in rice and seashore paspalum, whereas downregulating expression of PvCML9 showed increased salt tolerance in seashore paspalum as compared with the wild type (WT), indicating that PvCML9 regulated salt tolerance negatively. Na+ and K+ homeostasis was altered by PvCML9 expression. Lower level of Na+/K+ ratio in roots and shoots was maintained in PvCML9 -RNAi lines compared with WT under salt stress, but higher level in overexpression lines. Moreover, higher levels of SOD and CAT activities and proline accumulation were observed in PvCML9 -RNAi lines compared with WT under salt stress, but lower levels in overexpression lines, which altered ROS homeostasis. Based on the above data, mutation of its homolog gene OsCML9 in rice by CRISPR/Cas9 was performed. The mutant had enhanced salt tolerance without affecting rice growth and development, suggesting that OsCML9 gene is an ideal target gene to generate salt tolerant cultivars by genome editing in the future. • PvCML9 negatively regulated salt tolerance in seashore paspalum. • PvCML9 expression had reduced Na+ and K+ homeostasis under salt stress. • PvCML9 expression had also altered ROS homeostasis. • Consistently, PvCML9 negatively regulated salt tolerance in rice. • Mutation of OsCML9 led to enhanced salt tolerance without affecting rice growth and yield. [ABSTRACT FROM AUTHOR]

Calcineurin B-like-interacting protein kinase (CIPK) is a serine/threonine kinase, which transmits the Ca2+ signal sensed by CBL proteins. A CdtCIPK21 showing highly identical to OsCIPK21 in rice was isolated from triploid bermudagrass (Cynodon dactylon × Cynodon transvaalensis). CdtCIPK21 transcript could be detected in roots, rhizomes, stems, stolons, and leaves, with highest level in roots. It was induced by salinity, dehydration and chilling, but reduced by ABA treatment. Transgenic rice plants overexpressing CdtCIPK2 1 had decreased salt and drought tolerance as well as ABA sensitivity but increased chilling tolerance. Lower SOD and CAT activities was observed in transgenic lines under salinity and drought stress conditions, but higher levels under chilling stress. Similarly, lower levels of proline concentration and P5CS1 and P5CS2 transcripts were maintained in transgenic lines under salinity and drought stresses, and higher levels were maintained under chilling. In addition, transgenic lines had lower transcript levels of ABA-independent genes (OsDREB1A , OsDREB1B , and OsDREB2A) and ABA responsive genes (OsLEA3 , OsLIP9 , and OsRAB16A) under salinity and drought but higher levels under chilling compared with WT. The results suggest that CdtCIPK21 regulates salt and drought tolerance negatively and chilling tolerance positively, which are associated with the altered ABA sensitivity, antioxidants, proline accumulation and expression of ABA-dependent and ABA-independent stress responsive genes. [ABSTRACT FROM AUTHOR]

Abstract: Rice (Oryza sativa L.) roots were fed with l-ascorbic acid (AsA) and its putative precursors to observe AsA and oxalate concentrations and the resistance of rice to chilling, water stress, and Al toxicity. AsA concentration was significantly enhanced in both shoots and roots of rice seedlings by feeding with d-glucose or l-galactono-γ-lactone. AsA or l-galactono-γ-lactone treatment increased accumulation of oxalate mainly in soluble form, while these treatments decreased electrolyte leakage from root cells, H2O2 and lipid peroxidation level in rice seedlings subjected to chilling, water stress, and Al toxicity. They also alleviated the inhibition on root growth by Al. These results indicated that AsA and its immediate precursor protected plants against the oxidative damages induced by various stresses. However, 0.5 mM AsA and 10 mM l-galactono-γ-lactone treatment had no significant effect on superoxide dismutase and catalase activity and ascorbate-peroxidase activities. Enhanced Al resistance caused by AsA and l-galactono-γ-lactone may possibly be resulted from increased level of oxalate, which acts as metal chelator. Thus it is proposed that manipulation of AsA and oxalate biosynthesis through enhancement of l-galactono-γ-lactone level in plants could be a strategy for improving abiotic stress tolerance. [Copyright &y& Elsevier]