Salicylhydroxamic acid enhances the NADH-oxidase activity of peroxidase in pea mitochondrial and chloroplast suspensions

Effects of Superoxide Dismutase Inhibitors and Glucose on Cell Death and Generation of Reactive Oxygen Species in Pea Leaves

The effects of superoxide dismutase (SOD) inhibitors, diethyldithiocarbamate (DDC), triethylenetetramine (trien), and their combination with glucose on cells of the epidermis from pea leaves of different age (rapidly growing young leaves and slowly growing old leaves) was investigated. DDC and trien caused death of the guard cells as determined by destruction of their nuclei. Glucose did not affect destruction of the nuclei induced by SOD inhibitors in the cells from old leaves, but intensified it in the cells from young leaves. 2-Deoxyglucose, an inhibitor of glycolysis, and propyl gallate, SOD-mimic and antioxidant, suppressed destruction of the nuclei that was caused by SOD inhibitors and glucose in cells of the epidermis from the young, but not from the old leaves. Glucose and trien stimulated, and propyl gallate reduced generation of reactive oxygen species (ROS) in the pea epidermis as determined by the fluorescence of 2',7'-dichlorofluorescein (DCF). Carbonyl cyanide m-chlorophenylhydrazone (CCCP), a protonophoric uncoupler of oxidative and photosynthetic phosphorylation, suppressed the DCF fluorescence in the guard cells. Treatment of the cells with CCCP followed by its removal with washing increased destruction of the nuclei caused by SOD inhibitors and glucose. In young leaves, CCCP was less effective than in old ones. The findings demonstrate the effects of SOD inhibitors and glucose on the cell death and generation of ROS and could indicate glycolysis-dependent ROS production.

Ethylene mediates salicylic-acid-induced stomatal closure by controlling reactive oxygen species and nitric oxide production in Arabidopsis

Both salicylic acid (SA) and ethylene induce stomatal closure and positively regulate stomatal immunity, but their interactions in guard cell signaling are unclear. Here, we observed that SA induced the expression of ethylene biosynthetic genes; the production of ethylene, reactive oxygen species (ROS) and nitric oxide (NO); and stomatal closure in Arabidopsis thaliana. However, SA-induced stomatal closure was inhibited by an ethylene biosynthetic inhibitor and mutations in ethylene biosynthetic genes, ethylene-signaling genes [RESPONSE TO ANTAGONIST 1 (RAN1), ETHYLENE RESPONSE 1 (ETR1), ETHYLENE INSENSITIVE 2 (EIN2), EIN3 and ARABIDOPSIS RESPONSE REGULATOR 2 (ARR2)], NADPH oxidase genes [ATRBOHD and ATRBOHF], and nitrate reductase genes (NIA1 and NIA2). Furthermore, SA-triggered ROS production in guard cells was impaired in ran1, etr1, AtrbohD and AtrbohF, but not in ein2, ein3 or arr2. SA-triggered NO production was impaired in all ethylene-signaling mutants tested and in nia1 and nia2. The stomata of mutants for CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) showed constitutive ROS and NO production and closure. These results indicate that ethylene mediates SA-induced stomatal closure by activating ATRBOHD/F-mediated ROS synthesis in an RAN1-, ETR1- and CTR1-dependent manner. This in turn induces NIA1/2-mediated NO production and subsequent stomatal closure via the ETR1, EIN2, EIN3 and ARR2-dependent pathway(s).