Development of Endopeptidase Activity in Cotyledons of Vigna mungo Seedlings: Effects of Exogenously Applied End-Products and Plant Hormones

Abstract

The development of endopeptidase activity in cotyledons of Vigna mungo seedlings was examined after application of exogenous amino acids, sugars and plant hormones. The endopeptidase activity in the cotyledons fell when germinating seeds were allowed to absorb a solution of amino acids at high concentrations, and it was postulated that this effect might have been caused in part by osmotic stress and in part by end-product repression. Protein immunoblotting with an antiserum against SH-EP, the major cysteine endopeptidase occurring in the cotyledons, showed that sugars and amino acids at high concentrations also delayed the post-translational processing of SH-EP intermediates. Endopeptidase activity equivalent to nearly twice that in controls was observed when GA3 was applied at 10 to 100 μM to cotyledons that had been detached from the embryonic axis. In addition, naphthaleneacetic acid at 1 to 100 μM, kinetin at 1 to 10 μM and jasmonic acid at 1 to 10 μM also increased the activity to a limited extent. Results of pulse-chase experiments suggested that the effect of GA1 on the endopeptidase activity in the detached cotyledons was attributable to suppression of the degradation of the enzyme. Protein immunoblotting revealed the presence of 34-kOa and 35-kDa intermediates of SH-EP in addition to previously reported 36-kDa and 43-kDa intermediates.