Plant Physiology 92:1029-1037 (1990)
© 1990 American Society of Plant Biologists
Development and Growth Regulation
Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.) 1
III. Sensitivity of Germination to Water Potential and Abscisic Acid during Development
Gregory E. Welbaum2,
Tahar Tissaoui3 and
Kent J. Bradford
Department of Vegetable Crops, University of California, Davis, California 95616
Muskmelon (Cucumis melo L.) seeds are germinable 15 to 20 days before fruit maturity and are held at relatively high water content within the fruit, yet little precocious germination is observed. To investigate two possible factors preventing precocious germination, the inhibitory effects of abscisic acid and osmoticum on muskmelon seed germination were determined throughout development. Seeds were harvested at 5-day intervals from 30 to 65 days after anthesis (DAA) and incubated either fresh or after drying on factorial combinations of 0, 1, 3.3, 10, or 33 micromolar abscisic acid (ABA) and 0, 0.2, 0.4, 0.6, or 0.8 megapascals polyethylene glycol 8000 solutions at 30°C. Radicle emergence was scored at 12-hour intervals for 10 days. In the absence of ABA, the water potential ( ) required to inhibit fresh seed germination by 50% decreased from 0.3 to 0.8 megapascals between 30 and 60 DAA. The inside developing fruits was from 0.4 to 1.4 megapascals lower than that required for germination at all stages of development, indicating that the fruit is sufficiently low to prevent precocious germination. At 0 megapascal, the ABA concentration required to inhibit germination by 50% was approximately 10 micromolar up to 50 DAA and increased to >33 micromolar thereafter. Dehydration improved subsequent germination of immature seeds in ABA or low . There was a linear additive interaction between ABA and such that 10 micromolar ABA or 0.5 megapascal osmotic potential resulted in equivalent, and additive, reductions in germination rate and percentage of mature seeds. Abscisic acid had no effect on embryo solute potential or water content, but increased the apparent minimum turgor required for germination. ABA and osmoticum appear to influence germination rates and percentages by reducing the embryo growth potential (turgor in excess of a minimum threshold turgor) but via different mechanisms. Abscisic acid apparently increases the minimum turgor threshold, while low reduces turgor by reducing seed water content.
2 Current address: Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0327.
3 Current address: Institut National Agronomique de Tunisie, 43 Avenue Charles Nicolle, 1002 Tunis, Tunisia.
1 Supported in part by a California Melon Research Board Grant to K. J. B., a Jastro-Shields Research Award to G. E. W., and Regional Research Project W-168.
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