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Development of Cotyledon Cell Structure in Ripening Phaseolus vulgaris Seeds

1968; Oxford University Press; Volume: 19; Issue: 1 Linguagem: Inglês

10.1093/jxb/19.1.64

1460-2431

Helgi Öpik,

Plant pathogens and resistance mechanisms

Changes in weight, nitrogen content, and cell fine structure were followed in ripening cotyledons of greenhouse-grown beans. The seeds mature within 53–56 days from flowering, cotyledon weight and nitrogen content increasing most rapidly between days 22 and 34. The cotyledon parenchyma cells first become very highly vacuolate, but soon the large vacuoles are divided up and converted to reserve protein bodies, while cell expansion continues. Vacuole subdivision is accompanied by synthesis of cytoplasm containing masses of rough-surfaced ER (endoplasmic reticulum), which persists till the cotyledons dry out, and presumably synthesizes the reserve protein. Starch grains grow within plastids to reach diameters of 50 μ. Young cotyledons are green but chlorophyll disappears when the seed dries. Most organelles are recognizable in dry cotyledon cells; the ER is, however, replaced by small vesicles. Ribosomes are dispersed free in the cytoplasm during dehydration; this could indicate a destruction of mRNA (messenger ribonucleic acid) in preparation for a switch to a different metabolic activity during germination. Some comparisons are drawn between cell fine structure in the cotyledons during ripening and germination.