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

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.