MOLECULAR ANALYSIS OF NATURAL LEAF SENESCENCE IN ARABIDOPSIS-THALIANA

We have analyzed macromolecular changes that are associated with natur al leaf senescence in Arabidopsis thaliana. The loss of chlorophyll th at is characteristic of leaf senescence is accompanied by a specific p attern of decline of total RNA and protein levels. We have constructed two cDNA libraries representing mRNAs from Arabidopsis leaves at diff erent senescence stages. Six cDNA clones corresponding to mRNAs that s ubstantially increase in abundance during senescence were isolated. Th e levels of these mRNAs remain elevated into the late stages of senesc ence when most of the chlorophyll and protein of the leaf has been deg raded. Six cDNA clones that correspond to mRNAs that exhibit contrasti ng behavior were also identified; the levels of these mRNAs decrease t o undetectable levels during senescence. The changes in the levels of these specific mRNAs during the course of senescence are presented. Th e results indicate that major changes in gene expression occur in Arab idopsis leaves during the process of senescence.