Possible effect of gibberellin on phytate degradation in germinating barley seeds

Changes in the contents of phytate (IP₆) and other phosphorus(P)-compoundsin germinating seeds of a huskless barley were investigatedin the embryo with scutellum (EM), the starchy endosperm (EN),and the aleurone layer with pericarp-testa (AL). More than 80%of the total P in the AL of 1-day germinated seeds was foundin acid-soluble organic P, most of which was IP₆. During germination,the IP₆ in AL decreased markedly with no accumulation of lessphosphorylated myo-inositols and Pi and acid-insoluble organicP increased in the EM. The total P in the EN of 1-day germinatedseeds was about one-third that in the AL, the greater part ofwhich was found in the acid-insoluble fraction and decreasedgradually during germination. Only a small amount of IP₆ couldbe detected in the EM and EN during the early stage of germination. IP₆ in AL of embryoless half-seeds incubated without gibberellicacid (GA₃) decreased slightly even after 6 days. Incubationwith 10 ppm GA₃ remarkably stimulated the IP₆ degradation. Thisstimulation was reduced, with no change in the Pi content, byabout 80–90% with 1 mM 6-methylpurine or 10 ppm cycloheximide.The addition of 0.1 M KH₂PO₄ caused a 4-fold increase in thePi content of AL in the presence of GA₃. In addition, it suppressedthe GA₃-dependent -amylase synthesis by about 20% and the GA₃effect on IP₆ degradation by about 50%. In light of these results, IP₆ seems to be hydrolyzed completelyinto Pi and myo-inositol within the aleurone tissue, and gibberellinseems to control this process. (Received August 24, 1979; )