ISOLATION OF CDNA CLONES FOR GENES SHOWING ENHANCED EXPRESSION IN BARLEY LEAVES DURING DARK-INDUCED SENESCENCE AS WELL AS DURING SENESCENCEUNDER FIELD CONDITIONS

Senescence of barley (Hordeum vulgare L. cv. Carina) primary foliage l eaves was induced by transfer of the plants into darkness for 2 d. Und er these conditions senescence was characterized by a light-reversible decline in the efficiency of photosystem II, and in chlorophyll and p rotein contents. To isolate senescence-associated genes a differential display of cDNA fragments amplified from reversely transcribed RNA wa s employed. By this method, gene expression in leaves of control plant s collected at the onset of the dark period was compared with gene exp ression in senescing leaves collected at the end of the extended dark period. The expression of the genes represented by various differentia lly displayed cDNA fragments was examined by Northern blot hybridizati ons with RNA derived from primary foliage leaves before and after indu ction of senescence by darkness. In order to test whether these genes with enhanced expression during dark-induced senescence also show enha nced expression during natural senescence, Northern blot hybridization s were carried out with RNA samples prepared from flag leaves of barle y plants during maturation and senescence under field conditions. Five of the cDNA fragments representing transcripts associated with dark-i nduced senescence, as well as with natural senescence, were selected a s probes for screening a cDNA library from senescent flag leaves. With one probe a larger cDNA including a complete open reading frame with homology to the sequence of a known proteinase inhibitor was found. An other cDNA isolated by this means showed high sequence similarity with a gene coding for a 4-hydroxyphenylpyruvate dioxygenase. The other th ree larger cDNA clones isolated by this procedure so far do not show s ignificant homologies with known sequences.