Physiological and biochemical changes associated with cotton fiber development - IX. Role of IAA and PAA

Fibers of three cotton cultivars Gossypium hirsutum hybrid-4 (H-4), hybrid-8 (H-8), and G. arboreum G. Cot-15 were analyzed to study the role of auxin in fiber elongation, in vitro and in vivo. The cultivars exhibited variation in final fiber length. Fibers were analyzed for growth, free and conjugated indole acetic acid (IAA) content and phenyl acetic acid (PAA) content during the entire period of their development. Antibodies against IAA and PAA were raised and endogenous contents of IAA and PAA were estimated by indirect ELISA. Cotton fiber development is divided into four phases viz. (i) initiation (0-3 days post-anthesis (DPA)), (ii) elongation (3-24 DPA), (iii) secondary thickening (18-42 DPA) and (iv) maturation (42 DPA onwards). During the phase of rapid cell elongation, water content increased and then decreased after the fiber entered the secondary thickening phase, in all three cultivars. A positive correlation between final fiber length and free and conjugated IAA and PAA content was observed. In in vitro grown fiber, media supplemented with IAA or napthyl acetic acid (NAA) significantly increased the length of fiber in middle and short staple cultivars, whereas PAA promoted fiber length in the short staple cultivar only. The results of cultured cotton fiber suggest an important role of auxin in cotton fiber development, which may help for the selection of gene(s) for better fiber development. (C) 2002 Elsevier Science B.V. All rights reserved.