Influence of Gibberellic and Abscisic Acids and the Growth Retardant, CCC, upon Plastid Development

Gibberellic acid (GA3) enhances ultrastructural morphogenesis of plastids in greening cereals whilst abscisic acid (ABA) and CCC have the reverse effect over a shorter period. GA3 application counteracts the ABA and CCC inhibition of membrane development and, over longer periods of greening, the fastest rate of chloroplast development is shown in the presence of both GA3 and ABA. Experiments with isolated etioplasts show that the ABA inhibition of development also occurs and can be counteracted with GA3 treatment but no individual enhancement of plastid morphogenesis by GA3 was detected. Ribulose 1,5-diphosphate carboxylase (RuDPC) acitvity was also increased with applications of GA3 and reduced with ABA treatment. The initial levels of RuDPC activity in the presence of CCC were concentration dependent; high in 10-3 M CCC and low in 10-6 M CCC but activity returned to normal levels after CCC application was stopped. Experiments with isolated etio-chloroplasts gave similar results but levels of RuDPC activity declined rapidly in both illuminated and un-illuminated incubated suspensions of intact etioplasts.