SummanyOhaetomorpha darwinii is a marine alga with large coenocytic cells. The cell sap contains about 540 mM potassium, 25 mM sodium, and 600 mM chloride, and the vacuole is 10 mY positive to the sea water. The potassium selectivity is due to an active inward pump and an outward sodium pump at the plasmalemma. The fluxes of potassium at the plasmalemma and tonoplast were about 100 and 150 pmoles/cm2/sec, and the fluxes of sodium at these membranes were about 100 and 4 pmoles/cms/sec, respectively. The potential differences at these boundaries were -35 mY and +45 mY. The cytoplasmic phase contained about 18 p.-equiv/g of potassium and 0·5-1·0 p.-equiv /g of sodium.Dinitrophenol reduced the flux of potassiuni at the plasmalemma, and the content of the cytoplasm fell to about 0·5 p.-equiv/g, but it did not induce a net flux from the vacuole. Sodium influx was not affected by dinitrophenol, but the content of the cytoplasm rose from 0·5 to 7 p.-equiv/g, due to inhibition of the sodium efflux.There were some anomalies in the results, i.e. the high potassium content of the cytoplasm, the high potential difference at the tonoplast, and the lack of any effect of dinitrophenol on the net fluxes. These problems are considered to be due to the organization of the cytoplasm.

No abstract

Protoplasts isolated from cotyledons of aseptically germinated cucumber seedlings were divided into three size classes. The relationships between tissue age, isolation procedure, yield and protoplast size were investigated. During germination and up to an age of 13 days, the percentage of protoplasts in each size class underwent considerable change with a big reduction in percentage of the largest protoplasts in older cotyledons. Protoplast size and yield could also be manipulated by varying the isolation technique. In this context, temperature, incubation time and shaker speed were significant. By selecting tissue of appropriate age and using a carefully selected isolation procedure the percentage of viable cucumber protoplasts with the ability to form a cell wall and divide can be increased considerably.

Multiple shoot formation was induced on different media from excised hypocotyl and the nodal cuttings from 5 year old trees of atemoya (Annona cherimola Mill × A. squamosa L.) cv. African Pride. The highest number of shoots were obtained from the distal part (section near the root) of the hypocotyl cultured at a photosynthetic photon flux (PPF) of 36 μmol m-2 s-1 on Murashige and Skoog basal medium (MS) supplemented with 2% sucrose, 2 mg L-1 6-benzylaminopurine (BAP), 0.5 mg L-1 6-furfurylaminopurine (kinetin), 0.1 mg L-1 biotin, 0.1 mg L-1 calcium pantothenate and solidified with 0.8% agar. The number of shoots of mature nodal cuttings cultured on modified MS medium, supplemented with 1 g L-1 ammonium nitrate and the above mentioned growth regulators and addenda, was higher than MS basal or Woody Plant Medium. Increasing the kinetin level increased the number of shoots and fresh weight. Increasing the BAP level above 2 mg L-1 decreased the number of buds, length of shoots and fresh weight. The shoots were incubated in liquid MS medium containing 50 mg L-1 indole-3-butyric acid (IBA) in the dark and after 3 days were transferred to MS basal medium in the light, supplemented with 0.25% activated charcoal and solidified with 0.8% agar. Forty per cent of the shoots rooted. The rooted plantlets were successfully transferred to soil and planted in the glasshouse and 70 per cent of them showed rapid growth. Root induction was improved by pretreatment of shoots in liquid MS containing IBA. The effects of adding cytokinins, biotin and calcium pantothenate to the hypocotyl sections at different PPF and the effect of ammonium nitrate on multiple shoot production by nodal segments of in vivo grown plants are reported.

Explants of cucumber seedlings having different lengths of hypocotyl attached were grown axenically on Murashige and Skoog medium supplemented with kinetin (2 mg L-1). Multiple shoots developed from the apical regions of all explants. In this tissue shoots may also develop at the base of the hypocotyl, but this response is strongly dependent upon the length of the hypocotyl. As the length of the hypocotyl increased beyond 5 mm, there was a rapid reduction in basal shoot numbers and a concomitant increase in root production. We suggest that these responses are related not to the ratio or concentration of endogenous growth regulators but to different regions of sensitivity to growth regulators along the hypocotyl.