Induction of Sensitivity to Gibberellic Acid in Developing Wheat Caryopses: Effect of Rate of Desiccation

Abstract

No change in the total β-amylase activity, attributable to the presence of 10-6 M gibberellic acid (GA3) in the incubation medium, was found in freshly harvested, de-embryonated, immature (11-38 days post-anthesis) caryopses of wheat. Significant amounts of GA3-induced α-amylase activity was found in 26-h incubates of similar caryopses which had been allowed to dry out either in the ear or detached from the ear. After 10 days of storage of detached immature caryopses in air of 99-100% relative humidity, de-embryonated half-caryopses responded to applied GA3 by producing α-amylase. More α-amylase was found in 26-h incubates if detached caryopses dried out slowly, but rapid desiccation led to little or no α-amylase being produced in the presence of GA3. Caryopses taken from ears cultured on 0.4 or 4% sucrose for 10 days did not respond to applied GA3 whereas those from ears cultured on water did respond, although the amount produced in 26-h incubates was not as large as those from slowly dried ears. Development of the ability to respond to GA3 by increasing α-amylase activity depended on the duration of desiccation or isolation from the plant. Changes in metabolism emanating from the interruption to the supply of sucrose to the caryopsis may be involved in the development of the ability of the aleurone to respond to GA3.

Integrated control of seed maturation and germination programs by activator and repressor functions of Viviparous-1 of maize.

“…2). Our results are consistent with findings that a-amylase genes are not expressed in the developing seed (Nicholls 1979;Cornford et al 1986;Garcia-Maya et al 1990;Oishi and Bewley 1990). Hence, cessation of VP1 expression prior to germination may be necessary to allow induction of a-amylase genes in the germinating seed.…”

“…5). This suggests that expression of VP1 in the developing seed may be, at least in part, responsible for the GA insensitivity of cereal and maize a-amylase genes prior to seed maturity (Nicholls 1979;Cornford et al 1986;Garcia-Maya et al 1990;Oishi and Bewley 1990). In our experiments, VP1 displayed full repressing activity in sln mutant barley seeds (Fig.…”

“…In the developing seed, a-amylase activity is absent prior to seed maturity (Wilson et al 1973;Evans et al 1975). Moreover, a-amylase genes are unresponsive to applied GA (Nicholls 1979;Cornford et al 1986;Garcia-Maya et al 1990;Oishi and Bewley 1990). It has been suggested that the presence of ABA in developing seeds is responsible for the inhibition of a-amylase genes at this developmental stage (King 1976).…”

Distinction between the Responses of Developing Maize Kernels to Fluridone and Desiccation in Relation to Germinability, α-Amylase Activity, and Abscisic Acid Content

“…Nicholls (17) offers evidence that detachment from the plant, possibly due to an interruption of the flow of photosynthate, is sufficient to trigger a-amylase synthesis by developing wheat aleurone tissue. In this study, we detached cobs from the plant but kept them hydrated for a period equivalent to the drying treatment; there is no resulting responsiveness of the aleurone layer as far as a-amylase activity is concerned.…”

“…13), also play a role in the aleurone layer. Drying, when prematurely imposed on developing grains, enables the aleurone layer of wheat and barley to respond to GA and produce a-amylase (1,2,5,17), a starch-hydrolyzing enzyme which is the predominant protein synthesized by this tissue (6). Drying, it is argued, renders the tissue sensitive to gibberellin (1,5).…”