HEAVY-METAL-RESPONSIVE GENES IN MAIZE - IDENTIFICATION AND COMPARISONOF THEIR EXPRESSION UPON VARIOUS FORMS OF ABIOTIC STRESS

To identify genes involved in defense against heavy-metal stresses, a cDNA library originating from mercuric chloride-treated maize (Zen may s L. cv. INRA 258) leaves was constructed and analysed by differential screening using cDNAs derived from treated and untreated plants. Tran scriptionally activated cDNA clones, designated CHEM (chemically-activ ated), were isolated and characterized. They represent various known p roteins, such as glycine-rich proteins, pathogenesis-related proteins, chaperones and membrane proteins. The expression of the genes encodin g these proteins was studied in maize subjected to other forms of abio tic stress. Expression of glycine-rich proteins was greatly enhanced b y heat stress, and also stimulated by NaCl, polluted rainwater, woundi ng and cold stress. Pathogenesis-related proteins were strongly induce d by ultraviolet light and to a lesser extent by NaCl, polluted rainwa ter and wounding. Heat-shock protein was mainly induced by heat and co ld, and ubiquitin by wounding. Expression of the membrane channel prot ein was stimulated by heat stress, NaCl, polluted rainwater and ultrav iolet-light irradiation.