CULTURED OVULES AS MODELS FOR COTTON FIBER DEVELOPMENT UNDER LOW-TEMPERATURES

Cotton fibers (Gossypium hirsutum L.) developing in vitro responded to cyclic temperature change similarly to those of field-grown plants under diurnal temperature fluctuations. Absolute temperatures and rates of temperature change were similar under both conditions. In vitro fibers exhibited a "growth ring" for each time the temperature cycled to 22 or 15-degrees-C. Rings were rarely detected when the low point was 28-degrees-C. The rings seemed to correspond to alternating regions of high and low cellulose accumulation. Fibers developed in vitro under 34-degrees-C/28-degrees-C cycling developed similarly to constant 34-degrees-C controls, but 34-degrees-C/22-degrees-C and 34-degrees-C/15-degrees-C cycling caused delayed onset and prolonged periods of elongation and secondary wall thickening. Control fiber length and weight were finally achieved under 34-degrees-C/22-degrees-C cycling, but both parameters were reduced at the end of the experiment under 34-degrees-C/15-degrees-C cycling. Fibers developed under all conditions had equal bundle tensile strength. These results demonstrate that: (a) cool temperature effects on fiber development are at least partly fiber/ovule-specific events; they do not depend on whole-plant physiology; and (b) cultured ovules are valid models for research on the regulation of the field cool temperature response.