Salt-Induced Ultrastructural Damage to Mitochondria in Root Tips of a Salt-Sensitive Ecotype of Agrostis Stolonifera

In root tips of a salt-sensitive ecotype of Agrostis stolonifera,treatment with 100 mmol I^–1 NaCl for two weeks resultedin conspicuous structural damage to mitochondria, which becamedeficient in cristae, swelled and vacuolated. A salt-tolerantecotype maintained normal root tip mitochondrial structure underthe same salt treatment, in spite of accumulating higher levelsof sodium and chloride in its roots. The subcellular distributionof chloride, as judged by electron microscopy after precipitationwith silver ions, was identical in both ecotypes.     

Changes in Cell Fine Structure in the Cotyledons of Phaseolus vulgaris L. during Germination

When germination begins, the storage cells of Phaseolus vulgariscotyledons are packed with starch grains and protein bodies.Digestion of these reserves starts in cells furthest away fromthe vascular bundles and is practically completed in eight daysat 25° C. After the reserves are hydrolysed, the storagecells die. The changes in fine structure during the processof digestion and protoplasmic breakdown are described. Vascularbundle and epidermal cells survive till the cotyledons absciss,but in these tissues also profound changes occur in cellularorganization. The observations on fine structure are discussedwith reference to the metabolic activities of the cotyledons.     

The Fine Structure of some Dry Seed Tissues Observed after Completely Anhydrous Chemical Fixation

Completely anhydrous fixation with acrolein vapour or osmiumtetroxide vapour was applied to tissues of air-dry seeds: thecoleoptile of wheat (Trilicum aestivum), and plumule and radicleof mung bean (Vigna radiata). Great shrinkage of cells and organelleswas noted, but all the usual organelles could be identified,except for Golgi bodies and (in most cases) ribosomes. The endoplasmicreticulum was very abundant and endoplasmic reticulum tubuleswere closely associated with the storage organelles, namelylipid bodies in the wheat coleoptile, and protein bodies inthe mung bean embryo axis. Aqueous fixation resulted in considerabledistortion of cellular structure. Triticum aestivum L., wheat, Vigna radiata L., mung bean, seed, fine structure, anhydrous fixation     

Development of Cotyledon Cell Structure in Ripening Phaseolus vulgaris Seeds

Changes in weight, nitrogen content, and cell fine structurewere followed in ripening cotyledons of greenhouse-grown beans.The seeds mature within 53–56 days from flowering, cotyledonweight and nitrogen content increasing most rapidly betweendays 22 and 34. The cotyledon parenchyma cells first becomevery highly vacuolate, but soon the large vacuoles are dividedup and converted to reserve protein bodies, while cell expansioncontinues. Vacuole subdivision is accompanied by synthesis ofcytoplasm containing masses of rough-surfaced ER (endoplasmicreticulum), which persists till the cotyledons dry out, andpresumably synthesizes the reserve protein. Starch grains growwithin plastids to reach diameters of 50 µ. Young cotyledonsare green but chlorophyll disappears when the seed dries. Mostorganelles are recognizable in dry cotyledon cells; the ER is,however, replaced by small vesicles. Ribosomes are dispersedfree in the cytoplasm during dehydration; this could indicatea destruction of mRNA (messenger ribonucleic acid) in preparationfor a switch to a different metabolic activity during germination. Some comparisons are drawn between cell fine structure in thecotyledons during ripening and germination.     

Water Content and Respiration Rate of Bean Cotyledons

The course of water uptake and respiration rate rise in cotyledonsof Phaseolus vulgaris is divided into three phases. In the first phase lasting 10–16 hrs. respiration rateis controlled by water content; desiccation and reimbibitioninfluence cotyledon water content and respiration rate alikeand the changes are reversible; low temperature prevents watercontent rising above 50 per cent. and also limits respirationrate; both processes have Q₁₀ near unity. The second phase lasting 3–8 hrs. is characterized bya pause in both water uptake and respiration rate rise. In the third phase respiration rate continues to rise untilthe fifth day, after which it falls steadily until eventuallythe cotyledons absciss. The period of rising respiration isone of metabolic activity, the rise having a high Q₁₀ and beingprevented by low temperature. Desiccation at this stage is irreversible.