Abscisic acid aleurone layer

Roles of Metabolites of Abscisic Acid. Nothing is known about the physiological role of PA and DPA in plants, although these two metabolites of ABA have been tested in several bioassays recently. In the cotton explant abscission assay PA had one-tenth of the activity of ABA (19). PA and DPA were equally effective in inhibiting a-amylase secretion by barley aleurone layers treated with glbberellin A3 DPA had approximately one-tenth of the activity of ABA in this system (74). The effect of PA on growth of bean embryos was negligible (75). 

Ho, D. T. Response of barley aleurone layers to abscisic acid. Plant Physiol., 1976, 57, 175-178. 

Induction of de novo synthesis of a-amylase by GA in isolated aleurone layers is evident after a lag period of approximately 8 hr following administration of the hormone. In keeping with hormone responses generally, GA must be present continuously if the de novo synthesis of hydrolases is to be sustained. Synthesis of new RNA is essential to the GA-induction of de novo synthesis of hydrolases. Actinomycin D, an inhibitor of RNA synthesis, inhibits the synthesis and release of a-amylase if the inhibitor is presented during the first 7 to 8 hr after treatment. Inhibitors of protein synthesis, such as cycloheximide, also inhibit GA-induction of hydrolases. And, interestingly, abscisic acid, a growth-inhibiting hormone, inhibits GA-induced a-amylase synthesis as well. 

Regulation of Gene Expression by Abscisic Acid in Barley Aleurone Layers... 

Fig. 7.1. (A) Time course of a-amylase release by 10 aleurone layers of Himalaya barley incubated with 1 iM GA. Enzyme activity measured in the medium surrounding the aleurone layers and in the supernatant of a 0.2 M NaCl extract of the aleurone layers. Total refers to the sum of these two activities. After Chrispeels and Varner, 1967 [22]. (B) Midcourse inhibition of a-amylase production and release by abscisic acid and cycloheximide. Aleurone layers were incubated in 0.1 pM GA for 11 h and then 5 pM abscisic acid or lOpg/ml cycloheximide was added (arrowed). After Chrisppels and Varner, 1967 [23]... 

Cytokinins have also been reported to increase PA biosynthesis in some plant systems, while application of abscisic acid (ABA) leads to the contrary situation (see review in Smith, 1985a). For instance, benzyladenine increased putrescine and ADC activity in cucumber cotyledons. By contrast, ABA decreased putrescine and ADC activity (Suresh et ai, 1978 In rice seedlings, total PAs increased threefold after treatment with kinetin, but declined with ABA (Mukho-padhyay et ai, 1983). It has been proposed that the regulation of PA biosynthesis by ABA in the aleurone layers of barley seeds is exerted through inhibition of the conversion of putrescine to spermidine (Lin, 1985). 

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