Relationship between seed reserves and germination in triploid watermelon.

摘要

Triploid (seedless) watermelon seeds do not germinate well in the greenhouse, due to their erratic seed structure and sensitivity to the environment. The major seed reserves, including lipid and starch, may also play an important role in the physiological and biochemical control in the poor germination of triploid seeds.; Fatty acid profiles of triploid watermelon seeds revealed that the major fatty acids were palmitic, stearic, oleic and linoleic acids. Major increases in relative amounts of linoleic acid were noted with corresponding decreases in the other fatty acids, and fatty acid content was particularly high in triploids with low germination. Starch content was lower in triploids than diploids.; Ultrastructural studies offer a chance to examine diversities of the major reserve organelles in the cotyledon cells of triploid watermelon seeds. At the light microscope level, cotyledon cells were characterized by abundant protein bodies that were the most discernible organelle. At the electron microscope level, starch granules in triploids with high germination were significantly larger in diameter when compared to those with low germination, whereas lipid bodies in triploids with high germination were significantly smaller than those with low germination. Irregularly shaped lipid bodies were also observed in triploids. The differences found in the cotyledon cells of triploids might indicate more storage of lipid reserves and less availability of starch reserves in triploids with low germination during seed metabolism.; In comparison to diploids, the respiration quotient associated with O ₂ uptake and CO₂ release could account for large amounts of lipids relative to carbohydrates in triploid seeds, which suggested more oxygen is needed to break down lipids during germination. The changes of isocitrate lyase activity after 3 days of germination might be potentially affected by the fatty acid levels, especially high linoleic acids in triploids with low germination.; Therefore, the high linoleic acid found in triploids (especially low germination lots) and low starch content observed in triploid seeds in comparison to diploids, could be physiologically relevant to poor performance of germination.