Morphological and biochemical characterization of the cool temperature hindrance of early fiber elongation of cotton using ovules cultured in vitro as a model system



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Texas Tech University


Cool temperatures limit cotton yield and fiber quality. The effect is especially severe in major temperate cotton-producing regions such as the Texas High Plains. Cotton (Gossypiwn hirsutum L. cv Acala SJ-1) ovules cultured in vitro, were used to study the effeas of cool temperatures on fiber initiation and elongation. *Ovules, which produce normal fibers as in planta, were cultured 1 day before or on the day of anthesis under constant 15°C or 34°C or 12 hr/12 hr cycling at 15/34°C or 34/15°C. The similar initiation patterns observed by scanning electron microscopy (SEM) in vivo and in vitro confirm previous evidence that cultured ovules are valid models for fiber development research. * SEM and ruler measurement data indicated that there are three stages of fiber elongation as distinguished by different temperature responses: initiation, early elongation to attain a length of 0.5-3 mm, and later elongation to attain the genetically determined potential length. Initiation and early elongation were delayed 2-3 days by the low cycling temperature, but later elongation occurred at similar rates under cycling and constant 34°C regimes. The results provide direct evidence to confirm hypotheses derived fix)m field data. Further comparative analyses included determination of peroxidase activity and of profiles of newly synthesized proteins labeled with 35s-methionine to elucidate mechanisms underlying the initial delay and eventual acclimation in the elongation rate. Peroxidase activity was developmentally delayed and constantiy depressed under 15/34°C and 15°C compared to 34°C. One and two dimensional gel fluorographs of proteins labeled at the 34°C side showed that the 15/34°C cycling caused a developmental delay in the change of particular proteins, which correlated temporally with the temperatureinduced difference in timing of fiber initiation and early elongation, but no new proteins were detected by the labeling at the warm side of the cycle. However, 15°C specifically enhanced and suppressed the synthesis of some proteins, reduced total protein synthesis, and caused differences in mRNA populations. *Other labeling experiments demonstrated that a 15°C-induced unique 12 kD protein was degraded at 34°; this protein may aid fiber elongation recovery under the cool cycling regime. In contrast, only a few high molecular weight proteins syntiiesized at 34°C showed slight reduction in intensity upon shifting into 15°C. Therefore, degradation of proteins syntiiesized at 34°C by 15°C is not major cause of initial elongation delay.' We concluded tiiat the primary effect of 15°C is to inhibit and delay the synthesis of a set of proteins that may be important in normal fiber development