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 diumal 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/22 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.