Response to Darkness of Late-Responsive Dark-Inducible Genes is Positively Regulated by Leaf Age and Negatively Regulated by Calmodulin-Antagonist-Sensitive Signalling in Arabidopsis thaliana

Induction after prolonged darkness distinguishes the late-responsive genes din2 and din9 from the early-responsive gene din3 in Arabidopsis. The former genes were coincidently induced with the senescence marker gene YLS4 in rosette leaves of different ages and in the early-senescence mutant hys1. The calmodulin antagonists W-7, trifluoperazine, and fluphenazine accelerated the expression of the former genes in darkness but not in light, and had little effect on the latter gene. Our results suggest that Ca 2 + / calmodulin signalling conveys a negative signal that suppresses the responses of late-responsive din genes to prolonged darkness. The results are discussed in relation to natural senescence.