Role of growth regulators in the senescence of <i>Arabidopsis thaliana</i> leaves

Abstract

A homozygous, dominant, C 2 H 4 ‐resistant line of Arabidopsis thaliana (L.) Heynh (cv. Columbia; er ) was selected from ethylmethylsulfonate‐mutagenized seed, and used to test the role of C 2 H 4 and other growth regulators in senescence of mature leaves. Chlorophyll (Chl) loss from disks excised from leaves of er was much slower than that from wild‐type (WT) disks, whether they were held in the light or in the dark. C 2 H 4 accelerated Che loss from WT disks but had no effect on the yellowing of mutant disks. C 2 H 4 biosynthesis was higher in disks from the mutant plants, particularly in the light. In the dark, treatment with the cytokinin, 6‐benzyladenine (BA), reduced Chl loss from wild‐type disks, but had no effect on mutant disks. In the light, BA treatment stimulated chlorophyll breakdown in both wild type and mutant disks. Treatment with abscisic acid (ABA) stimulated chlorophyll loss in wild‐type and mutant disks, whether they were held in the light or the dark. C 2 H 4 production was stimulated in ABA‐treated disks, but they still yellowed even when C 2 H 4 production was inhibited by application of aminooxyacetic acid (AOA). These data indicate that C 2 H 4 is only one of the factors involved in leaf senescence, and that the promotion of senescence by ABA is not mediated through its stimulation of C 2 H 4 production.