The influence of the embryonic axis and cytokinins on reserve mobilization in germinating lupin seeds

Abstract

The influence of the embryonic axis and cytokinins (CKs) on reserve mobilization has been examined in yellow lupin (Lupinus luteus L. cv. JSG 6167) seed during germination and during early growth for up to 9 d in the dark. The study included determination of starch, soluble sugars, proteins, and amino acid content. Amylolytic and proteolytic enzyme activity was also measured in untreated cotyledons with intact embryo (attached) or detached cotyledons (embryo removed), and in detached cotyledons following treatment with CKs namely, dihydrozeatin, (diH)Z, and 6-benzylaminopurine, BAP. Generally, the detached cotyledons showed reduced mobilization and decreased enzymatic activity in comparison to attached cotyledons, indicating the importance of the embryonic axis in this process. However, a rise in protease activity and free amino acid content was detected in 9-d-old detached cotyledons suggesting that the end products do not necessarily inhibit enzyme activity. While (diH)Z was partially effective in inducing reserve mobilization and enzymatic activity in detached cotyledons, the effect'of BAP was more pronounced and appeared to replace the embryonic axis. The embryonic axis of this species has recently been shown to synthesize CKs which are transported to the cotyledons, are highly stable and induce cotyledon expansion and chlorophyll synthesis. The results of the present investigation and previous studies from this laboratory collectively indicate that the regulation of reserve mobilization in yellow lupin seeds appears to be mediated, at least in part, by a stimulus, probably a CK, emanating from the embryonic axis