Exogenous auxin affects ascorbate metabolism in roots of tomato seedlings

Abstract

Ascorbate levels and redox states, as well as the activities of the enzymes of ascorbate metabolism, were analyzed in roots of tomato seedlings during the culture on a medium supplemented with auxin and compared to the control cultured on an auxin-free medium. Biochemical parameters were determined separately in the distal part of the root where the inhibitory effect of auxin on root elongation growth is observed and in the proximal half on the organ which reacts to auxin treatment with increased lateral root proliferation. ASC peroxidase activity was found to be stimulated by auxin treatment in the lateral-root forming part of the root. This effect was not observed in the distal part of the organ. On the other hand, ASC oxidase activity was raised by auxin exclusively in the distal part of the root. An inhibitory effect of auxin supplementation to the medium on ASC-reducing enzymes was observed. The dehydroascorbate reductase activity was found to be inhibited by auxin only in the proximal part, while the activity of monodehydroascorbate reductase in both, the proximal and distal parts of the root. Ascorbate content increased in roots during culture irrespective of the presence of auxin. However, auxin treatment resulted in higher DHA levels and more significant participation of DHA in the total ascorbate pool when compared to the control grown on the auxin-free medium. Similar to auxin, adding DHA to the culture medium stimulated lateral root formation and inhibited primary root elongation. In contrast to DHA, ASC treatment affected significantly neither lateral root formation nor primary root growth and partly reversed the stimulatory effect of IAA on root formation and the inhibitory effect on root elongation. These results suggest that auxin induced changes in ascorbate metabolism may be involved in developmental reactions in tomato roots.

The effect of natural and synthetic auxins on the growth, metabolite content and antioxidant response of green alga Chlorella vulgaris (Trebouxiophyceae)

“…Ascorbate derives its role from its sensitivity to ROS and from the fact that its oxidation affects the redox balance of other metabolites, such as glutathione which themselves are involved in the perception of the cellular redox unbalance (Apel and Hirt 2004). Our results are supported by the data obtained by Tyburski et al (2008) indicating that the presence of exogenous auxin in the culture induced an increase in ascorbate level in the roots of tomato seedlings.…”

Exogenous auxin regulates H2O2 metabolism in roots of tomato (Lycopersicon esculentum Mill.) seedlings affecting the expression and activity of CuZn-superoxide dismutase, catalase, and peroxidase

“…In our previous study we reported on the fact that auxin stimulates the activity of ascorbate peroxidase (APX). In contrast to CAT, auxin induced an increase in the activity of this enzyme in the proximal part of the root (Tyburski et al 2008).…”

Glutathione and glutathione disulfide affect adventitious root formation and growth in tomato seedling cuttings

“…These data suggest that the process of root elongation is dependent on optimal GSH level in the growing part of the organ and that the mechanism of inhibition of root growth by auxin may possibly involve the accumulation of supraoptimal GSH levels. Other redox factors such as ROS (Joo et al 2001;Liszkay et al 2004) and ascorbate (Tyburski et al 2008) were also found to be implicated in the inhibition of root elongation by exogenous auxin. Fig.…”