Temporal Changes in Protein and Proteolytic Enzyme Activities in Germinating Cotton Axes

Eugene L. Vigil and Tung K. Fang


Radicle emergence during germination of cotton seeds is an important first step in crop stand production. The presence of stored lipid and protein in cortical cells of the axis suggested the possibility that utilization of these reserves provides nutrients for axial elongation. In a test of this hypothesis, intact and excised axes from cotton (Gossypium hirsutum L. var M-8) seeds were exposed for 24 hr to standard germination test conditions of 100% humidity and 30°C. Analysis of elongation growth after 24-h imbibition revealed that axes changed in length from 3.9 mm (0 hr) to 10.5 mm (24 hr), increased in per cent moisture from 7.6 % to 76.4 % and protein content (ug/axis) went from 874.0 to 859.0. Similar changes occurred in excised radicles after 24 h imbibition. Data for specific activity for of aminopeptidase, endopeptidase and carboxypeptidase in whole cell extracts from axial and cotyledonary samples from dry seeds and after 24 hr imbibition revealed that activities for these enzymes increased dramatically in axes compared to cotyledons in parallel with utilization of stored reserves. SDS-PAGE of extracted protein from 0 and 24 hr imbibed seeds provided complementary evidence for selective reduction in the 52 kD storage protein in axes but not cotyledons. Additional support for initial utilization of storage proteins in axes over cotyledons was obtained from electron microscopy. These results indicate that there is a causal relationship between utilization of stored protein and axial elongation which affect the radicle protrusion process associated with late germination. Nutrient contribution from cotyledons appears to be minimal to this phase of cotton seed germination. Supported in part by a grant from Cotton Incorporated

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 1338
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998