An Assessment ofα‐Tubulin Isotype Modification in Developing Cotton Fiber

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Abstract
Multiple isoforms of α‐ and β‐tubulin accumulate in higher plant cells, including cotton (Gossypium hirsutum L.) fiber. Isotypes may originate either by transcription of distinct genes or by posttranslational modification of gene products. The existence of two types of posttranslational modification in cotton fiber α‐tubulin has been examined by immunoblotting cotton fiber proteins from two developmental stages and by probing with specific monoclonal antibodies to acetylated (6‐11B‐1) or tyrosinated (YL 1/2 ) α‐tubulin. Control experiments were conducted with an antibody (YOL 1/34) that recognizes a conserved region in plant and animal α‐tubulins. No acetylated forms of α‐tubulin were found in either of two varieties of cotton fiber at 10 or 20 d postanthesis. One isotype of α‐tubulin, isotype 6, failed to cross‐react with YL 1/2 at 10 d postanthesis, which indicated that the protein was detyrosinated, and isotype 8 appeared to be detyrosinated at 20 d postanthesis. Since the carboxyl terminus of higher plant α‐tubulin is exposed on the surface of microtubules, removal of the carboxyl‐terminal amino acid may lead to some of the changes in the structure and organization of microtubules that are associated with fiber development.