Control of Protein Hydrolysis in the Cotyledons of Germinating Pea (Pisum sativum L.) Seeds

Abstract

The effects of removal of the shoot or whole axis on the levels of total, protein, and TCA-soluble nitrogen and on protease activity in cotyledons during germination of garden pea ( Pisum sativum L ) seedlings grown in the light have been examined. Removal of the shoot 1 week after soaking the seed caused a reduction in the rates of protein hydrolysis and of nitrogen transport from the cotyledons and an increase in the level of soluble nitrogen When the entire axis was excised after 4 or 9 days there was a great reduction in protein hydrolysis while the level of soluble nitrogen remained the same as in de-shooted plants. In the intact plant, proteolytic activity of cotyledon extracts rose to a peak about 15 days after soaking of the seed and then fell rapidly This fall coincided with a decrease in water content and in oxygen consumption by the cotyledons. Removal of the shoot or entire axis led to a much smaller and more gradual increase in protease activity and the subsequent decline in activity of the enzyme and senescence of the cotyledons were also delayed. It is concluded that control of protein hydrolysis in pea cotyledons is not mediated through the level of protease enzymes, as indicated by the proteolytic activity of tissue extracts, or by the amount of soluble nitrogen compounds accumulated. Protease activity seems to be controlled by the shoot and to be closely linked to senescence of the cotyledons Protein hydrolysis and transport of nitrogen to the axis, on the other hand, are affected by the presence of both shoot and root and the axis appears to exert independent control on each of these processes.