Differential response of maize catalases and superoxide dismutases to the photoactivated fungal toxin cercosporin

Abstract

Summary Many fungi of the genus Cercospora produce a light‐induced, photoactivated polyketide toxin called cercosporin. In the presence of light an excited form (triplet state) of the toxin molecule is produced which, depending on the reducing potential of the environment, reacts with molecular oxygen to produce singlet oxygen and/or superoxide radicals. In this paper a system is presented for analysis of antioxidant defense gene response using purified cercosporin under conditions demonstrated to favor superoxide formation. Under the assay conditions employed, changes in total catalase activity, as well as individual isozyme protein levels generally mirrored the changes observed in corresponding steady‐state RNA levels in response to applied cercosporin. In contrast, while transcript accumulation for most maize superoxide dismutases increased dramatically, both total superoxide dismutase activity and individual isozyme protein levels remained constant in all toxin treatments. In one case, the analyses indicated that there are two distinct transcripts that hybridize with a gene‐specific probe for Sod3. These two transcripts responded differentially to applied toxin (levels of the larger transcript increased while the smaller decreased), whereas corresponding steady‐state levels for the SOD‐3 isozyme proteins remained constant. This suggests that protein turnover might play a role in the response of these SODs to activated oxygen species.

Reactive oxygen species‐mediated enzymatic systems involved in the oxidative action of 2,4‐dichlorophenoxyacetic acid*

“…The lower level of the CuZn-SOD mRNA in plants treated with 2,4-D, might be due to a higher instability of the mRNA favoured by the herbicide. Similar discrepancies between SOD transcript levels and activities have been also found in pine tree, maize and tobacco plants exposed to different stress conditions (Williamson & Scandalios 1992;Karpinski et al 1992;Zhu & Scandalios 1994;Savouré et al 1999). Regarding other antioxidative systems, catalase (CAT) activity in pea leaves was not changed significantly by the herbicide treatment, but its specific mRNA content was notably enhanced by 2,4-D. An induction of the genes Cat1, Cat2 and Cat3 was found in maize immature embryos treated with auxins -either IAA or 2,4-D -, and a parallel increase in the activity of the respective isozymes was also detected (Guan & Scandalios 2002).…”

Salt-induced antioxidant metabolism defenses in maize (Zea maysL.) seedlings

“…1 This requirement would be a consequence of the highly active electron transfer reactions involved in superoxide dismutation that would cause protein inactivation. 34 Similar data, increased mRNA accumulation in parallel to unaltered SOD protein levels, were reported in NaCl-stressed N. plumbaginifolia. 15 Abscisic acid (ABA) is a plant growth regulator involved in many growth and developmental processes.…”

“…8 Increases in SOD transcript steady-state levels were not accompanied by increases in enzymatic activity, similar to SOD responses to fungal toxin. 34 and Mn-SOD responses to ABA and high osmoticum. 10 A high protein turnover has been suggested to keep up with a higher demand of SOD activity on stressful conditions.…”

Nitric Oxide Signalling In Plants

“…Although total and Cu,Zn-SOD activities stayed steady during the hypersensitive response, analysis of Cu,Zn-SOD transcript accumulation showed a strong and sustained induction within 1 h of the treatment of the avirulent pathogen. This reveals that protein income might play a role in the response of Cu,Zn-SOD to activate oxygen or nitrogen species (Williamson & Scandalios, 1992). LSD1, a negative regulator of cell death, regulates SA induction of Cu,Zn-SOD (Kliebenstein et al, 1998) in an O 2 − -dependent signal (Jabs et al, 1996) and provisions the future role for SOD as a modulator of O 2 − function.…”