Factors that influence the longevity and senescence of photosynthetic tissues of Arabidopsis were investigated. To determine the influence of reproductive development on the timing of somatic tissue senescence, the longevity of rosette leaves of the Landsberg efecta strain and of isogenic mutant lines in which flowering is delayed (co-2) or sterile flowers are produced (ms7-7) were compared. No difference in the timing of senescence of individual leaves was observed between these lines, indicating that somatic tissue longevity is not governed by reproductive development in this species. To examine the role of differential gene expression in the process of leaf senescence, cDNA clones representing genes that are differentially expressed in senescing tissues were ísolated. Sequence analysis of one such clone indicated homology to previously cloned cysteine proteinases, which is consistent with a role for the product of this gene in nitrogen salvage. RNA gel blot analysis revealed that increased expression of senescence-associated genes is preceded by declines in photosynthesis and in the expression of photosynthesis-associated genes. A model is presented in which it is postulated that leaf senescence is triggered by age-related declines in photosynthetic processes.

~~~The relationship between fruit development and the proliferative capacities of inflorescence meristems has been examined in Arabidopsis fhaliana. In the wild-type Landsberg erecta (Ler) line, flower production ceases coordinately on all inflorescence branches by a process we have designated global proliferative arrest (CPA). Morphological studies indicate that CPA involves a cessation of proliferative activity at the meristems, but a retention of the structural characteristics of the proliferating meristems. CPA does not occur in the male-sterile (msl-7) line, nor in wild-type Ler when fruits are surgically removed. In these cases, inflorescence meristems continue to proliferate, ultimately terminating by a different process, designated terminal differentiation, in which disruptions in patterning at the apex are followed by the loss of the inflorescence meristem. We present an argument that CPA is mediated by a specific communication system between inflorescence meristems and developing fruits. Analysis of reduced-fertility mutants provided evidence that CPA is dependent on seed development specifically. Mutations conferring hormone deficiency or insensitivity did not disrupt the correlative interactions leading to CPA.

Factors that influence the longevity and senescence of photosynthetic tissues of Arabidopsis were investigated. To determine the influence of 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 timing of senescence of individual leaves was observed between these lines, indicating that somatic tissue longevity is not governed by reproductive development in this species. To examine the role of differential gene expression in the process of leaf senescence, cDNA clones representing genes that are differentially expressed in senescing tissues were isolated. Sequence analysis of one such clone indicated homology to previously cloned cysteine proteinases, which is consistent with a role for the product of this gene in nitrogen salvage. RNA gel blot analysis revealed that increased expression of senescence-associated genes is preceded by declines in photosynthesis and in the expression of photosynthesis-associated genes. A model is presented in which it is postulated that leaf senescence is triggered by age-related declines in photosynthetic processes.

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