Role of abscisic acid in cotton fiber development

Fibers of three cotton cultivars varying widely in their final fiber length, i.e., long staple (Gossypium hirsutum H-4), middle staple (G. hirsutum H-8), and short staple (G. arboretum G. Cot-15) were analyzed to study the role of ABA in fiber elongation and dry matter accumulation, in vivo and in vitro. The fibers were analyzed for different growth parameters and endogenous ABA content during the entire period of their development using indirect ELISA by raising the antibodies against ABA. From growth analysis, cotton fiber development was divided into four distinct phases, (i) initiation, (ii) elongation, (iii) secondary thickening, and (iv) maturation. An inverse correlation between final fiber length and ABA content was observed in all the cultivars. In long staple cultivar (H-4), rapid ABA accumulation started after fiber had attained peak elongation growth while, in short staple cultivar (G. Cot-15), ABA accumulation was observed even during elongation growth. Significant inhibition in length of short and middle staple cultivars as compared to long staple cultivar was observed in in vitro grown fibers when media were supplemented with ABA (1, 3, and 5 mg/l). The addition of growth promoters like NAA and GA, along with ABA, has reduced the inhibition in fiber elongation in all the cultivars. These results suggest a regulatory role of ABA in cotton fiber elongation along with auxins and gibberellins.