Ascorbate‐glutathione cycle and H2O2 detoxification in elongating leaf bases of ryegrass: effect of inhibition of glutathione reductase activity on foliar regrowth

Abstract

The role of the ascorbate‐glutathione cycle and AOS detoxification was investigated during leaf growth of defoliated and undefoliated plants of ryegrass (Lolium perenne L. cv. Bravo). Antioxidants and related enzymatic activities were located in elongating leaf bases (ELBs) of undefoliated plants, following a decreasing gradient from basal (meristem) to distal segments, inverse to H2O2 levels. In the meristematic zone, the intense activity of the ascorbate‐glutathione cycle and the supply of reducing power by the oxidative pentose phosphate pathway allowed the maintenance of both antioxidant reduction and H2O2 detoxification. BCNU (1–3 bis(2‐chloroethyl)‐N‐nitrosourea), a glutathione reductase inhibitor, induced an increase in the meristematic zone in both H2O2 and antioxidant levels and a decrease in reduced/oxidized ratios of glutathione and ascorbate. These changes were associated with a reduced foliar regrowth activity. In the absence of BCNU, defoliation did not modify the ratios of reduced/oxidized antioxidants, although it triggered a temporary increase in H2O2 level. The results are discussed on the basis of a possible control of leaf growth by glutathione and ascorbate.