Regulation of Fiber Cell Initiation by Early- Season Temperatures in American Upland Cotton

The components of lint yield in cotton are the number of plants per acre, the number of bolls per plant, the number of seeds per boll, and the number of fibers per seed. This list may be reduced to the two essential components, i.e., the number of seeds per acre and the weight of fiber per seed. A great deal of attention has been paid to the first factor but the weight of fiber per seed has been grossly neglected. A recent report (Lewis, 2000a) presented strong evidence that variations in daily minimum temperatures early in seedling development dramatically influence the expression of genes that control the number of fiber cell initials in the outer integuments of the egg sac apparatus of American upland cotton (Gossypium hirsutum). This finding is in good agreement and strongly supports the findings of Zeevart (1966) concerning the role of temperature and day length in regulating differentiation of plant reproductive tissue. Specifically, the proposition that the mechanism by which these environmental factors exert their influence involves the activation of specific gene loci. The earlier report (Lewis, 2000a) involved dividing the whole plant into “Fruiting Zones,” which involved combining fiber from multiple bolls from different fruiting positions for subsequent analyses. This procedure could yield results which masked or obscured possibly important differences in fiber parameters from boll to boll in a given “fruiting zone”. Because of this possibility, the experiment reported in this study was designed to examine individual bolls from single fruiting positions in “Fruiting Zone I”, that is, the first four first-position bolls. This paper reports the results from this study.