Effect of temperature on the decomposition of reserves during germination and early growth of rice plants - An electron microscopic study

Morphological changes in starch granules in endosperm cells of rice, cv. Cisadane (javanica) and cv. Koshihikari (japonica), during germination and early growth of seedlings at 17degreesC, ambient temperature (Field condition, 16-24degreesC) and 38degreesC, respectively, were examined with scanning and transmission electron microscopes. With the treatment at 17degreesC, a groove-like structure appeared on the surface of amyloplasts at Five days after seeding (DAS). After the amyloplast envelope disappeared and starch granules were separated from each other, small holes, which were observed at higher temperatures, did not appear, and a "rough structure" appeared on the granule surface. At 15 DAS, starch granules adjacent to scutellum were partly decomposed but those at the distal end of the seed did not decompose until 15 DAS. In the seed germinated at 38degreesC, starch granules in endosperm cells adjacent to scutellum began to decompose within one day after seeding, and small holes appeared on the surface of starch granules. At further stages of decomposition, a layer-like structures was observed inside of the starch granule that followed by the appearance of highly viscous materials on the resolving granules and decomposed almost completely at 15 DAS. At this time, many mitochondria that seemed to be related with decomposition of starch granules were observed by transmission electron microscopy. At an ambient temperature, the decomposition has progressed at 15 DAS with the vanishing of amyloplast envelopes in the whole of endosperm. In cv. Koshihikari most of the starch granules had decomposed at 20 DAS.