The knockdown of chloroplastic ascorbate peroxidases reveals its regulatory role in the photosynthesis and protection under photo-oxidative stress in rice

The inactivation of the chloroplast ascorbate peroxidases (chlAPXs) has been thought to limit the efficiency of the water-water cycle and photo-oxidative protection under stress conditions. In this study, we have generated double knockdown rice (Oryza sativa L.) plants in both OsAPX7 (sAPX) and OsAPX8 (tAPX) genes, which encode chloroplastic APXs (chlAPXs). By employing an integrated approach involving gene expression, proteomics, biochemical and physiological analyses of photosynthesis, we have assessed the role of chlAPXs in the regulation of the protection of the photosystem II (PSII) activity and CO2 assimilation in rice plants exposed to high light (HL) and methyl violagen (MV). The chlAPX knockdown plants were affected more severely than the non-transformed (NT) plants in the activity and structure of PSII and CO2 assimilation in the presence of MV. Although MV induced significant increases in pigment content in the knockdown plants, the increases were apparently not sufficient for protection. Treatment with HL also caused generalized damage in PSII in both types of plants. The knockdown and NT plants exhibited differences in photosynthetic parameters related to efficiency of utilization of light and CO2. The knockdown plants overexpressed other antioxidant enzymes in response to the stresses and increased the GPX activity in the chloroplast-enriched fraction. Our data suggest that a partial deficiency of chlAPX expression modulate the PSII activity and integrity, reflecting the overall photosynthesis when rice plants are subjected to acute oxidative stress. However, under normal growth conditions, the knockdown plants exhibit normal phenotype, biochemical and physiological performance.

Effect of heat-shock induced oxidative stress is suppressed in BcZAT12 expressing drought tolerant tomato

The transcription factor ZAT12 is a member of stress-responsive C2H2 type zinc finger protein (ZFP) reported to control the expression of stress-activated genes mediated via ROS in plants. BcZAT12-transformed tomato cv. H-86, var. Kashi vishesh (lines ZT1-ZT6) over-expressing the gene product is demonstrated herein to be tolerant to heat-shock (HS)-induced oxidative stress. Results reveal that the relative expression of ZAT12 as well as heat induced Hsp17.4 and Hsp21 gene transcripts increased in transgenic upon exposure to HS. The transformed tomato lines ZT1 and ZT5 had significantly lowered free radical formation, improved electrolyte leakage, relative water content and chlorophyll levels with an enhanced activities of antioxidant enzymes viz. superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase when exposed to HS. HS-induced oxidative stress by over-expression of the BcZAT12 gene transcripts in tomato as well as by largely enhancing the ROS-scavenging capacity and up regulation of Hsp transcripts. This enables the transgenic tomato plants to acquire a greater ability to counteract HS-induced oxidative stress, being endowed with more reduced antioxidant pools. The use of these HS-tolerant tomato lines could possibly be used for tomato cultivation in the areas affected by sudden temperature changes.