The tomato Cu,Zn superoxide dismutase genes are developmentally regulated and respond to light and stress

Abstract

The expression of the two Cu,Zn superoxide dismutase (SOD) genes of tomato was followed in different organs and plant developmental stages at the transcript and enzymatic activity levels. The cDNA clones used as probes code for the chloroplast Cu,Zn SOD (clone T1) and the cytosolic Cu,Zn SOD (clone P31). The two genes were found to display distinct expression patterns. While the T1 transcript was rare or absent from roots, stems and ripening fruits, the P31 transcript was very abundant in these organs. Shoot tips, flower buds, seedlings and young leaves contained high levels of the two mRNAs. During leaf expansion, the levels of both transcripts diminish markedly. Despite the diminished presence of transcripts, SOD activity levels of the corresponding cytosolic and chloroplast isozymes accumulated and were sustained throughout leaf expansion. In non-photosynthetic organs, the SOD-3 (cytosolic) isozyme contained most of the activity, while in the expanded leaf the SOD-1 (chloroplast) isozyme was more abundant. Light-regulated accumulation of both the P31 transcript (1.7-fold) and the T1 transcript (3-fold) was observed upon light exposure of etiolated seedlings. However, only SOD-1 activity was observed to increase, after a lag of a few hours. The levels of both transcripts increased in response to paraquat and mechanical wounding. The level of the cytosolic transcript and the respective isozyme activity increased dramatically during prolonged drought stress while the chloroplast transcript remained unaffected. The expression of both genes was enhanced by spraying tomato plants with ethephon--a compound that releases ethylene. Our data show that the expression of Cu,Zn SOD genes in tomato is modulated in response to a variety of factors and suggest the importance of oxyradical toxicity as well as the role of SOD in the defence mechanism of plants exposed to stress.

Regulation of pea cytosolic ascorbate peroxidase and other antioxidant enzymes during the progression of drought stress and following recovery from drought

“…It is possible that the high levels of Apxltranscript observed in response to other environmental stresses (Mittler and Zilinskas, 1992) might have also been restricted from interaction with polysomes. Such a mechanism for regulation of antioxidant enzymes may also apply to other systems in which similarly large differences were observed between stress-induced increase in steady-state transcript levels and increase in protein and/or activity (Bowler et a/., 1989;Perl-Treves and Galun, 1991;Williamson and Scandalios, 1992).…”

“…Drought stress was chosen for two reasons: (i) episodes of water deficiency are among the most common environmental stresses encountered by plants during their growth period; and (ii) drought stress is believed to be accompanied by the production of activated oxygen species and has been reported to result in increased activity of antioxidant enzymes (Mittler and Zilinskas, 1992;Perl-Treves and Galun, 1991;Smirnoff and Colombe, 1988;Tanaka eta/., 1990). Drought stress, as indicated by a decrease in leaf water potential and stomatal closure (especially at D2 and D3, Figure I ) , resulted in an increase in cytosolic APX and Cu/Zn-SOD gene expression and in an increase in catalase activity.…”

Light and Excess Manganese

“…Although Cu/Zn-SOD II did not respond to Mn toxicity, one might not rule out a direct effect of excess Mn in the chloroplast of mature leaves. Even with oxidative stress caused by paraquat, which is believed to target the chloroplast, increases in cytosolic and plastidic Cu/Zn-SOD have been reported (Perl-Treves and Galun, 1991). Aono et al (1991) showed that transformed plants expressing bacterial GR in the cytosol were more resistant to paraquat than untransformed plants.…”

Impact of drought and leaf development stage on enzymatic antioxidant system of twoPopulus deltoides×nigraclones

“…Thus, reaction to drought was clone, leaf age-and drought intensity-dependant: SOD and catalase activities were stimulated during severe drought in the mature leaves of the tolerant clone 'Dorskamp', while peroxidase seemed favored during mild drought in the expanding leaves of the more susceptible clone 'Luisa_Avanzo'. Stimulation of the antioxidant enzymatic activities of the Halliwell-Asada pathway has commonly been observed in response to drought [14,16]. Nevertheless, the implication of these enzymes under drought conditions has been shown to be diverse according to species and/or to drought intensity [18].…”