Fine Structure in Cells of Pea and Wheat Embryos

Self Cite

Isolated nuclei and nucleoli of ungerminated pea embryos have been analyzed chemically for their content of DNA, RNA, zinc, iron, phosphorus, and protein sulfhydryl groups. The values obtained cannot be considered to represent the whole of the riving nucleolar body as an undetermined amount of material is extracted from nucleoli in the course of their isolation. Only negligible amounts of DNA have been found in the isolated nucleofi; most of the DNA released on disruption of nuclei appears in a fraction showing very few structures under the light microscope. RNA is more concentrated in the nucleolus than in the nucleus or cytoplasm, but since nucleolar protein is 6 per cent of nuclear and less than 1 per cent of cytoplasmic protein, the total amount of nucleolar RNA is comparatively small. None of the other components listed occurs in high concentration in either nucleus or nucleolus.

Section: Resultssupporting

confidence: 61%

Some Chemical Properties of Isolated Pea Nucleoli

Stern

Johnston

Setterfield

1959

Self Cite

“…Setterfield et al . (38) studied the ultrastructure of pea and wheat embryos moistened on damp filter paper for 4 hr, but they did not follow developmental changes during germination .…”

Section: Introductionmentioning

confidence: 99%

Ultrastructural Changes in Cells of Pea Embryo Radicles During Germination

Yoo

1970

Radicles (I mm long) of pea embryo axes, excised from dormant seeds and from seeds soaked for 80 min, 8, 12, and 48 hr, were fixed in glutaraldehyde and postfixed in OSO4 . The nucleus was only slightly changed by 48 hr soaking, but cytoplasmic organelles underwent developmental changes . There was proliferation of endoplasmic reticulum, the appearance of dictyosomes, and an inward migration of lipid bodies . Most of these changes were observed within 8 hr after soaking started . Plastids, mitochondria, protein bodies, and protein crystalline bodies were also identified and their developmental changes were followed .

“…However, within 12 to 24 hours after the seeds had imbibed water, mitochondria in cells became visible, presumably arising de novo. Thus, it is obvious that changes occur quite rapidly in seeds after imbibition of water.Unfortunately, most electron microscope studies have been conducted on seeds which were allowed to imbibe water for various periods prior to fixation (16,18,25,28). Since rapid changes do occur in seeds upon imbibition of water, any technique involving imbibition of water, even for short periods, may not reflect their original condition.…”

mentioning

confidence: 99%

THE ULTRASTRUCTURE OF COTYLEDONARY TISSUE FROM GOSSYPIUM HIRSUTUM L. SEEDS

Yatsu

1965

Quiescent cottonseeds stored in a dry, anaerobic situation for over a year have been shown to contain cells whose contents are ultrastructurally similar to those of normal, fully hydrated plant cells. Plastids, mitochondria, and nuclei of the cells of cotyledon tissue in dry seeds possess normal-looking double membranes even under conditions of extreme desiccation. Previous reports have indicated on the basis of light microscopic work, that the cells of certain dry seeds do not possess nuclear membranes or mitochondria. The cells of the dry cottonseed do contain these structures, however. Dictyosomes have not been observed in the spongy parenchymal cells of the cotyledon tissue; it is suggested that they are concerned with translocation and/or utilization of material. The storage materials in the cells, protein and oil, are contained in vacuolar areas enclosed by a single membrane.Seeds offer a convenient base line in ontogenetic studies of the plant. Many ultrastructural studies have been directed to the terminal stages of seed development (7,8,12,17,27) or to the initial stages of seed germination (4,10,18,22,28), but relatively few studies have been conducted on the dry seed per se. Yet an understanding of the final changes on maturation and the first events of germination requires information on the mature, quiescent seed as a point of reference.Studies of biochemical changes in seeds which have initiated germination processes (1, 9, 31) show a dramatic rise in activity of many enzymes within a very short time. Wasserman (29), working with light microscopy, was unable to see mitochondria in cells of the dry seed. However, within 12 to 24 hours after the seeds had imbibed water, mitochondria in cells became visible, presumably arising de novo. Thus, it is obvious that changes occur quite rapidly in seeds after imbibition of water.Unfortunately, most electron microscope studies have been conducted on seeds which were allowed to imbibe water for various periods prior to fixation (16,18,25,28). Since rapid changes do occur in seeds upon imbibition of water, any technique involving imbibition of water, even for short periods, may not reflect their original condition. The paucity of studies on dry seeds is probably due to the extreme difficulty of working with them. This study, therefore, was undertaken to determine the structure of cells in dry, quiescent seeds fixed directly without prior hydration. MATERIALS AND METHODSA master sample of cottonseed (Gossypium hirsutum L., var. Acala 4-42-77, Glandless) harvested in Fall, 1962 was stored in a vacuum desiccator with a desiccant at 3°C and subsamples were removed as needed. Sections of tissue approximately 0.3 mm in diameter were cut carefully from the seed and fixed immediately in two different fixatives, osmium tetroxide and permanganate salts. OSMIUM :Since earlier work indicated that various solvents deranged the normal structure of the dry