Physiological and biochemical changes associated with cotton fibre development

Growth kinetics and levels of auxin substances were studied in three cotton cultivars, designated as long, medium and short staple cultivars. Fibre length and dry weight plotted against boll age showed sigmoidal patterns and were fitted to a logistic curve by computer curvilinear regression analysis. The final length of the fibre in different cultivars was the product of the rate of elongation per day and the total period of elongation. Further, considerable overlap between the elongation and the secondary thickening phases was recorded. No relationship between auxin substances and rate of fibre elongation was discernible. The peak levels of auxin substances in all the cultivars were recorded before or about the time when elongation had just started, and it is concluded that the auxin synthesized during the elongation phase is consumed in elongation growth. Thus there is necessarily no relationship between remaining auxin and growth.