Differential Protein Pattern of Two Cotyledon Explants of Vigna radiata During Induced In Vitro Differentiation: Probable Implication in the Conundrum of Differential Regeneration Response

Abstract

Differential regeneration response in two cotyledon types (Cot and Cot E) of Vigna radiata was reported earlier. The Cot (one cotyledon) is easily detachable from the germinating embryonal axis, whereas, Cot E (the other cotyledon) remains firmly attached during seed germination or after imbibition. Shoots differentiated directly from the Cot E under the induction of in vitro differentiation, while, under the same milieu, shoot differentiation was preceded by callus differentiation from Cot. In this study, we present comparative analyses of protein profiles from these two explant types recorded at different point of time during induction of differentiation. Cot E always contained higher amounts of soluble protein than the Cot. Likewise, higher de novo protein synthesis was noted in Cot E than in Cot as revealed by ³⁵S methionine labeled study. Two polypeptides of ∼37 and 84 kD disappeared earlier from Cot E than Cot and is presumed to be linked with shoot induction. Two marker proteins of ∼88 and 158 kD synthesized during shoot differentiation were apparent. It was observed that the labeled protein synthesis initiated within 3h in Cot E under in vitro condition, while, no labeled protein was detected from Cot even at 12h. Irrespective of the mode of differentiation, a large amount of protein was hydrolyzed during the process of differentiation. However, in case of Cot, the process was delayed by a day than Cot E. In all probability, this is an indication of delayed cytokinin induced rejuvenation of Cot. Temporal difference in protein profile was also evident in these two explant types during in vitro differentiation. Yet, three major groups of proteins were consistently present in both the explants. The biochemical differences recorded between these two explants during induction of in vitro differentiation reflects the temporal difference in gene expression. Perhaps Cot E has the distinctiveness due to the temporal differences in certain key gene expression and proved its greater suitability over Cot for shoot regeneration purposes.