Increasing the glutathione content in a chilling-sensitive maize genotype using safeners increased protection against chilling-induced injury

With the aim of analyzing their protective function against chilling-induce d injury, the pools of glutathione and its precursors, cysteine (Cys) and g amma -glutamyl-Cys, were increased in the chilling-sensitive maize (Zea may s) inbred line Penjalinan using a combination of two herbicide safeners. Co mpared with the controls, the greatest increase in the pool size of the thr ee thiols was detected in the shoots and roots when both safeners were appl ied at a concentration of 5 muM. This combination increased the relative pr otection from chilling from 50% to 75%. It is interesting that this increas e in the total glutathione (TG) level was accompanied by a rise in glutathi one reductase (GR; EC 1.6.4.2) activity. When the most effective safener co mbination was applied simultaneously with increasing concentrations of buth ionine sulfoximine, a specific inhibitor of glutathione synthesis, the tota l gamma -glutamyl-Cys and TG contents and GR activity were decreased to ver y low levels and relative protection was lowered from 75% to 44%. During ch illing, the ratio of reduced to oxidized thiols first decreased independent ly of the treatments, but increased again to the initial value in safener-t reated seedlings after 7 d at 5 degreesC. Taking all results together resul ted in a linear relationship between TG and GR and a biphasic relationship between relative protection and GR or TG, thus demonstrating the relevance of the glutathione levels in protecting maize against chilling-induced inju ry.