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.     

Physiological and biochemical changes associated with cotton fibre development

The relationship between growth and some enzymes of carbohydrate metabolism in developing cotton fibre were studied. Two respiratory pathways of glucose oxidation i.e. oxidative pentose phosphate pathway (OPPP) and glycolysis operates in the elongating cotton fibres and the extent of their operation varies with the demand for respiratory products. In this respect, hexokinase, G-6-PDH, 6PGDH, and MDH show increased activities during the period of rapid cell elongation and decreased activities when rate slows down. The conversion of PEP to malate and/or via a transhydrogenase system consisting of enzymes PEPC, MDH and NADP-MDH(d) may play a significant role in carbohydrate compartmentation of developing cotton fibre. As the rate of fibre growth slows down, a decline in enzyme activities, points to a shift in metabolic priorities.     

Physiological and biochemical changes associated with cotton fiber development. VIII. Wall components

Fibers of three cotton cultivars (Gossypium hirsutum L.) H-4, H-8 and (G. arboreum) G. Cot-15, which shows variation in staple length were analyzed for growth in terms of fiber length and fresh and dry mass. From the growth analysis cotton fiber development is divided in four distinct phases i.e. (i) initiation (ii) elongation (iii) secondary thickening and (iv) maturation. Rate of fiber elongation and rate of water content shows close parallelism. Highly esterified and less esterified pectic fraction along with high and low molecular weight xyloglucan fractions were estimated from fiber walls of all the three cotton genotypes. Xyloglucans were fractioned in to high and low molecular weight by alkali treatment, 1 M and 4 M KOH respectively. Xyloglucan content shows inverse correlation with fiber elongation. Role of water content and wall components in determination of staple length in cotton genotypes is discussed.