Embryo is not required for initiation of ⍺-amylase activity in germinating cowpea (Vigna unguiculata L.) seeds

Abstract

When embryonated and de-embryonated cotyledons of cowpea (Vigna unguiculata L.) were kept for germination, only embryonated cotyledons (EC) developed into seedlings. ⍺-Amylase activity appeared late in de-embryonated cotyledons (DEC), but increased and matched with that of EC on 4th day, and thereafter started declining. A higher content of reducing sugars may be one of the factors in down regulating the activity in DEC after 4th day, in comparison to EC, where it continued increasing. Addition of GA₃ to DEC did not increase the activity significantly, suggesting that GA₃ was not a limiting factor for amylase initiation. Addition of 1 mM chlorocholine chloride (CCC) to DEC decreased activity by about 50%, suggesting that GA₃ might partly be synthesized in the DEC and hence the activity could be initiated independent of embryo. However, for mobilization of starch, amylase activity has to be sustained for a longer period, for which sink strength in the form of shoot and root is essential. Unlike cereals, where embryo is required for induction of amylase, the process of amylase induction in germinating cowpea seeds appear to be different. Purification of ⍺-amylase from EC and DEC by DEAE-cellulose and Sephadex G-150 column chromatography revealed three peaks in EC, and only one in DEC, indicating that gibberellin present in DEC could induce only one form of amylase. Amylase from DEC had higher Km value (0.33 mg ml⁻¹ of starch), as compared to the corresponding Km value in EC (0.11 to 0.16).