Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2001
Publication Date: N/A
Interpretive Summary: Plants experience high air and soil temperatures during periods of drought and when fields receive limited irrigation. These stresses frequently coincide in areas with hot arid climates where one stress can serve to compound the effects of the other. Similar to mature plants, germinating seed and seedlings can also be subjected to environmental stresses. Upon imbibing water, seeds may be exposed to a hostile environment including extremes of temperature and moisture, and failure to cope with such adversity results in poor seedling development and eventually reduced crop yields. This study evaluated the affect of water-deficit stress on the expression of a high temperature protection system that exists in cotton. The study showed that water-deficit stress reduced overall plant performance, but the level of acquired thermotolerance was proportional to that of well-watered seedlings. The study also showed that heat shock proteins that accumulate in seeds as a part of normal seed development and are lost from seeds within a few days of germination, remained in the cotyledons of water-stressed cotton seedlings several days longer than in the well-watered seedlings. Unfortunately, the presence of these developmentally regulated heat shock proteins failed to enhance inherent or acquired thermotolerance compared with well-watered cotton seedlings. These findings support the hypothesis that the developmentally-regulated heat shock proteins may be involved in desiccation tolerance in seeds, and are unavailable for enhancing heat tolerance in water-stressed seedlings.
Technical Abstract: Cotton seeds planted under dryland conditions frequently experience periods of water-deficit stress and elevated temperatures during seedling establishment. This study was conducted to determine the effect of water-deficit stress on the expression of cotton's acquired thermotolerance protection system. Germinating cotton seeds were water-stressed in either PEG solutions or vermiculite in the laboratory and their ability to induce thermotolerance upon exposure to elevated temperatures was evaluated using a chlorophyll accumulation assay. The results showed reduced seedling growth under water-deficit stress, yet the acquired thermotolerance system was not inhibited. Protein analysis at 5 days after planting showed that developmentally regulated HSP101 and HSP17.6 were present in the cotyledons of water-deficit stressed cotton seedlings, and that they were absent in cotyledons from well-watered seedlings. The presence of these HSPs in the water-deficit stressed seedlings failed to enhance inherent or acquired thermotolerance over well-watered seedlings. These results support the suggested role of developmentally-regulated HSPs in desiccation tolerance in seeds, and suggests that they are unavailable to function in enhancing thermotolerance.