Polyamine Metabolism and Its Relation to Response of the Aleurone Layers of Barley Seeds to Gibberellic Acid

Abstract

Polyamine metabolism and its relation to the induction of alpha-amylase formation in the aleurone layers of barley seeds (Hordeum vulgare cv Himalaya) in response to gibberellic acid (GA(3)) has been investigated. A high-performance liquid chromatographic system has been employed for qualitative and quantitative analyses of putrescine (Put), cadaverine (Cad), spermidine (Spd), spermine (Spm), and agmatine (Agm).Active polyamine metabolism occurs in the aleurone cells of deembryonate barley half seeds during imbibition. The aleurone layers isolated from fully imbibed half seeds contain about 880 nanomoles of Put, 920 nanomoles of Spd, and 610 nanomoles of Spm as free form per gram tissue dry weight while the levels of Cad and Agm are relatively low. The polyamine levels do not change significantly in the aleurone layers in response to added GA(3) (1.5 micromolar) during the 8-hour lag period of the growth substance-induced formation of alpha-amylase. Also, the polyamine levels are not altered by the presence of abscisic acid (3 micromolar) which inhibits the enzyme induction by GA(3). Kinetic studies show that both applied [U-(14)C]ornithine and [U-(14)C]arginine are primarily incorporated into Put during 2 hours of incubation, but the incorporation is not significantly affected by added GA(3). Additionally, added GA(3) does not affect the uptake and turnover of [1,4-(14)C]Put, nor does it affect the conversion of Put --> Spd or Spd --> Spm. Treatment of the aleurone layers with GA(3) for 2 hours results in no significant changes in the total activities or the specific activities of ornithine decarboxylase and arginine decarboxylase.Experiments with polyamine synthesis inhibitors demonstrate that the level of Spd in the aleurone layers could be substantially reduced by the presence of methylglyoxal-bis(guanylhydrazone) (MGBG) during imbibition. MGBG treatment does not affect in vivo incorporation of [8-(14)C] adenosine into ATP. The lower the level of Spd the less alpha-amylase formation is induced by added GA(3). The reduction of GA(3)-induced alpha-amylase formation by MGBG treatment can be either completely or partially overcome by added Spd, depending upon the concentration of MGBG used in the imbibition medium. The results indicate that the early action of GA(3), with respect to induction of alpha-amylase formation in barley aleurone layers, appears to be not on polyamine metabolism. However, polyamines, particularly Spd, may be involved in regulation of the growth substance-dependent enzyme induction.