Inhibition of glutathione synthesis reduces chilling tolerance in maize

The role of glutathione (GSH) in protecting plants from chilling injury was analyzed in seedlings of a chilling-tolerant maize (Zea mays L.) genotype using buthionine sulfoximine (BSO), a specific inhibitor of gamma-glutamylc ysteine (gamma EC) synthetase, the first enzyme of GSH synthesis. At 25 deg rees C, 1 mM BSO significantly increased cysteine and reduced GSH content a nd GSH reductase (GR: EC 1.6.4.2) activity, but interestingly affected neit her fresh weight nor dry weight nor relative injury. Application of BSO up to 1 mM during chilling at 5 degrees C reduced the fresh and dry weights of shoots and roots and increased relative injury from 10 to almost 40%. Buth ionine sulfoximine also induced a decrease in GR activity of 90 and 40% in roots and shoots, respectively. Addition of GSH or gamma EC together with B SO to the nutrient solution protected the seedlings from the BSO effect by increasing the levels of GSH and GR activity in roots and shoots. During ch illing, the level of abscisic acid increased both in controls and BSO-treat ed seedlings and decreased after chilling in roots and shoots of the contro ls and in the roots of BSO-treated seedlings, but increased in their shoots . Taken together, our results show that BSO did not reduce chilling toleran ce of the maize genotype analyzed by inhibiting abscisic acid accumulation but by establishing a low level of GSH. which also induced a decrease in GR activity.