Water Stress and Storage-protein Degradation during Germination of Impatiens Seed

Abstract

Water uptake by impatiens (Impatiens wallerana Hook. f. cv. Super Elfin Coral) seeds was measured as an increase in fresh weight every 24 hours during 144 hours of germination. Seeds absorbed most of the water required for germination within 3 hours of imbibition and germinated at 60% to 67% moisture on a dry-weight basis. Germination started at 48 hours and was complete by 96 hours at 25C. Water stress of -0.1, -0.2, -0.4, and -0.6 MPa, induced by polyethylene glycol 8000, reduced germination by 13%, 49%, 91%, and 100%, respectively, at 96 hours. Under the same water-stress conditions, increases in fresh weight were inhibited by 53%, 89%, 107%, and 106%, respectively. Three distinct groups of storage proteins were present in dry seed; their estimated molecular weights were 1) 35, 33, and 31 kDa; 2) 26, 23, and 21 kDa; and 3) two bands <14 kDa. Major depletion of storage proteins coincided with the completion of germination. Water potentials that inhibited germination also inhibited degradation of storage proteins. During germination under optimum conditions, the soluble protein fraction increased, coinciding with a decrease in the insoluble fraction.