Cycloheximide aleurone layer

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]... 

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. 

When applied to barley aleurone layers, gibberellic acid stimulated the incorporation of [met/iy/- CJcholine into PC (Evins and Varner, 1971). Absci-sic acid prevented this effect of gibberellic acid. Johnson and Kende (1971) showed that gibberellin stimulated both PC cytidyltransferase and choline phosphotransferase and that these stimulations could be prevented by absci-sic acid, cycloheximide, and actinomycin D. 

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