Protoplast Fusion: EFFECT OF LOW TEMPERATURE ON THE MEMBRANE FLUIDITY OF CULTURED CELLS

Combined electron-spin-resonance, X-ray-diffraction studies on phospholipid vesicles obtained from cold-hardened wheats : I. An attempt to correlate electron-spin-resonance spectral characteristics with frost resistance

Phospholipid multibilayers, obtained from two cultivars of thermally acclimated wheats of different frost resistances (Triticum aestivum L. cv. Penjamo 62, the sensitive cultivar, and T. aestivum L. cv. Miranovskaja 808, the frost-resistant cultivar), were investigated using electron-spin-resonance and X-ray-diffraction techniques. The former technique revealed two breaks in the motion of the spin-labelled fatty acid 2-(14-carboxyte-tradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxyl, for both cultivars (+3°C,-17° C and +5° C,-18° C, respectively) when grown at 22° C. The resistant cultivar compensated for exposure to cold (+2° C) by shifting the onset of the apparent phase-separation temperature from +3° C to-16° C. The sensitive cultivar was unable to do so. X-ray diffraction did not reveal fluid-to-gel transitions between +20° C and-10° C in any of the samples. The possible role of the formation of relatively ordered aggregates or clusters of lipid molecules discerned by spin probe within the otherwise freely dispersed liquid-like lipids is discussed in terms of freezing injury of plants.

Aggregation of plant protoplasts by artificial lipid vesicles

Sonicated unilamellar lipid vesicles, consisting of egg lecithin, stearylamine, and cholesterol in 7:2:1 molar ratios, promoted the aggregation of tobacco (Nicotiana glutinosa) protoplasts with the aid of mono- or divalent cations.A reaction mixture containing liposomes (0.4 micromoles lipid per milliliter), 50 millimolar CaCl(2), 0.5 molar mannitol, and 5 x 10(5) protoplasts per milliliter resulted in approximately 25% protoplast aggregation. To achieve the maximum protoplast aggregation, 1.6 x 10(8) liposomes per protoplast per hour would be required.The kind of liposomes effective in protoplast aggregation were positively charged, small-size vesicles which were obtained either by 60-minute sonication or by membrane filtration in conjunction with sonication.

Physiological Control of Chloride Transport in Chara corallina: I. EFFECTS OF LOW TEMPERATURE, CELL TURGOR PRESSURE, AND ANIONS

The rate of Cl(-) transport at the plasma membrane of the freshwater alga Chara corallina is investigated with respect to possible in vivo controls acting in addition to the two well established ones of cytoplasmic Cl(-) and cytoplasmic pH. In contrast with results from many other plant tissues, halides appear to be the only anions capable of inhibiting Cl(-) transport, either from the outside or inside surfaces of the plasma membrane. Cell turgor pressure was also investigated. It was found that neither the influx of Cl(-) nor that of K(+) or HCO(2) (-) is sensitive to turgor. Internal osmotic pressure is also insensitive to turgor, a situation contrasting with that in closely related brackish water charophytes.After temperature downshift (from 20-4 C) Cl(-) transport displays a slow, time-dependent rise. Return of cells from 4 C to 20 C results in a large stimulation of Cl(-) influx in comparison with cells maintained at 20 C throughout. This stimulation persists for several hours and is also apparent (to a reduced extent) in cells which have had cytoplasmic composition controlled by intracellular perfusion. The stimulation therefore arises, in part, from a change in plasma membrane properties. The results are discussed with respect to recent work on membrane fluidity as a function of temperature.