DEVELOPMENTAL AND AGE-RELATED PROCESSES THAT INFLUENCE THE LONGEVITY AND SENESCENCE OF PHOTOSYNTHETIC TISSUES IN ARABIDOPOSIS

Factors that influence the longevity and senescence of photosynthetic tissues of Arabidopsis were investigated. To determine the influence o f reproductive development on the timing of somatic tissue senescence, the longevity of rosette leaves of the Landsberg erecta strain and of isogenic mutant lines in which flowering is delayed (co-2) or sterile flowers are produced (ms1-1) were compared. No difference in the timi ng of senescence of individual leaves was observed between these lines , indicating that somatic tissue longevity is not governed by reproduc tive development in this species. To examine the role of differential gene expression in the process of leaf senescence, cDNA clones represe nting genes that are differentially expressed in senescing tissues wer e isolated. Sequence analysis of one such clone indicated homology to previously cloned cysteine proteinases, which is consistent with a rol e for the product of this gene in nitrogen salvage. RNA gel blot analy sis revealed that increased expression of senescence-associated genes is preceded by declines in photosynthesis and in the expression of pho tosynthesis-associated genes. A model is presented in which it is post ulated that leaf senescence is triggered by age-related declines in ph otosynthetic processes.