An ultrastructural study of chloroplasts and microbodies in seed and seedling cotyledons of Pharbitis nil
Riedell, Walter E.
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The cellular ultrastructure of cotyledon tissue from seeds and seedlings of Japanese morning glory (Pharbitis nil) was studied. Weight determinations of the seed and seedling cotyledons, the same age as those studied under the transmission electron microscope, indicate that the growing cotyledons of the seed and seedling increase in biomass. During this period of growth, cellular ultrastructure of the seed and seedling cotyledons undergo marked changes. Cells of the seed cotyledon 17 days after anthesis appear as highly vacuolate cells. The appearance of lipid and protein bodies in the cells of slightly older (30 days after anthesis) seed cotyledons corresponds to an increase in fresh weight and percentage dry weight of these slightly older seed cotyledons. Upon dark germination and subsequent irradiation with white light, the fresh weight of the seedling cotyledons increases steadily. Microbodies (glyoxysomes), which aid in the enzymatic breakdown of stored lipid, are present within the dark germinated seedling cotyledon cells. Irradiation of the seedling cotyledons with white light causes the de novo development of the peroxisomes. A description of the ultrastructure of the two types of microbodies, as well as semi-quantitative analysis of their characteristic associations with lipid bodies and chloroplasts is given. Chloroplasts of seed and seedling cotyledons, which undergo developmental changes when exposed to light, were also studied. The ultrastructural appearance of the chloroplasts, as well as the amount of chlorophyll present in seed and seedling cotyledons, indicate that the chloroplasts of both seed and seedling cotyledons are able to carry on the process of photosynthesis. Plastids of dark grown seedling cotyledon cells which were irradiated with continuous far red light undergo no structural transformation.