Cultured Ovules as Models for Cotton Fiber Development under Low Temperatures

Abstract

Cotton fibers (Gossypium hirsutum L.) developing in vitro responded to cyclic temperature change similarly to those of fieldgrown 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 150C. Rings were rarely detected when the low point was 280C. The rings seemed to correspond to alternating regions of high and low cellulose accumulation. Fibers developed in vitro under 34°C/280C cycling developed similarly to constant 340C controls, but 34°C/220C and 340C/15°C cycling caused delayed onset and prolonged periods of elongation and secondary wall thickening. Control fiber length and weight were finally achieved under 34°C/220C cycling, but both parameters were reduced at the end of the experiment under 34°C/150C cycling. Fibers developed under all condifions 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.The cotton fiber (Gossypium hirsutum L.) is an elongated epidermal cell of the cotton ovule with a thickened secondary wall composed of almost pure cellulose. Its development is characterized by two overlapping phases, primary wall synthesis to accomplish fiber elongation and secondary wall synthesis to accomplish fiber thickening (25). It has been known for decades that field-grown fibers exposed to cool temperatures (generally at night) have prolonged periods and reduced overall rates of elongation and thickening (9,10,14,28) and "growth rings" in their secondary walls (2,18 vidual fibers (1 1). However, little research has been directed toward determining the mechanism of this response despite its adverse economic consequences (8) and fundamental importance to understanding the regulation of cell wall deposition.The temperatures that affect wall deposition (e.g. 22°C) are well above those typically associated with chilling injury in plants, including cotton (12, 24), suggesting that a particular temperature-sensitive step might be identifiable. Differences between existing cultivars (9-11, 14, 28) shows that the cool temperature response has a manipulable genetic component. Ectothermic organisms such as plants are precisely adapted to regulate metabolism optimally at the temperatures normally encountered (16). There is evidence that plants are biochemically adapted to have relatively narrow temperature optima for certain enzymes, so that metabolism may not necessarily have a simple linear relationship with temperature (5). Since cotton evolved under hot subtropical temperatures, lowering the optimum temperature for certain processes might be possible if key regulatory genes could be identified, isolated from another organism with a lower temperature optimum, and tran...

A membrane-associated form of sucrose synthase and its potential role in synthesis of cellulose and callose in plants.

“…Ovules of G. hirsutum Acala SJ-1 were cultured in vitro until days 18-21 of fiber development at 34°C as described (21). Western blot analysis of proteins from cultured fibers showed a specific reaction of anti-SuSy antibody, but not preimmune serum, with one polypeptide as did proteins from plant-grown fibers (see below).…”

Effects of Cycling Temperatures on Fiber Metabolism in Cultured Cotton Ovules

“…Ovules from cotton (Gossypium hirsutum L. cv Acala SJ1) ovaries harvested 1 d after flower opening were used for the preparation of floating ovule cultures as previously described (17). To reduce variability between replicate observations, ovules from different ovaries and locules were randomized in culture vessels.…”

“…Fiber development is typically divided into two stages, primary wall formation (to accomplish elongation) and secondary wall synthesis (to accomplish fiber thickening) (24 Current address: University of Iowa, Ames, IA. lose in the secondary wall that is required for fiber maturation (10,17), and temperatures less than 250C are low enough to induce resistance to the deleterious effects of subsequent exposure to 50C in cotton seedlings (20). The research reported here is focused on the period of secondary wall deposition because of the adverse effect of cool night temperatures in northern cotton growing regions on fiber cell wall thickening, which is a major determinant of crop quality and value (10).…”

“…It is possible that identification of relevant mechanisms will allow future genetic engineering of cotton and other agriculturally important plants for improved yield under the diurnal temperature cycles that are frequently encountered in temperate agricultural regions. This mechanistic research has been greatly simplified by use of cultured ovules (2) of Gossypium hirsutum L. cv Acala SJ1, which have been shown to be valid models for the field response because secondary wall structure and accumulations of fiber length and weight respond similarly to diumal temperature fluctuations in vitro and in the field (17). Cultured ovules also offer the advantages of (a) ease of manipulation of temperature conditions in incubators; (b) ability to distinguish temperature effects specific to ovules and fibers from those that depend on 'whole plant' physiology; and (c) ability to determine biosynthetic rates by feeding the ovules radiolabeled substrate (6).…”

Cellulose structure and biosynthesis

“…For instance, in my home state of Texas, the quality of the cotton crop often is decreased when grown under cool night temperatures [37]. Regulating ®ber production and quality when plants are grown under stress conditions could signi®cantly improve the economics of cotton production.…”