Reversal points in cotton fibers may compromise fiber strength by generating regions of wall weakness. When viewed with polarized light, two types of reversals are observed: S and Z. This study investigated the effects of exogenously applied plant hormones on reversal frequency and type during secondary wall development in Gossypium hirsutum L. 'MD51'. The data indicate that reversal frequency increases and microfibril orientation changes as the secondary wall is deposited and walls thicken. Application of gibberellic acid (C19H22O6) (1.0 mg L-1) significantly increased total reversal frequency, whereas indole-3-acetic acid (C10H9NO2) (0.1 mg L-1) had no effect. Fibers treated with both gibberellic acid and indole-3-acetic acid exhibited significantly fewer Z reversals than untreated fibers at 50 d post-anthesis. During secondary wall synthesis, a relationship may exist between fiber elongation, reversal frequency, and reversal type. Our observations are consistent with previous suggestions that reversal points may be localized areas of cell expansion, arising from growth that occurs after the secondary wall is deposited. New insight into the factors that affect reversal frequency may be used to make a positive impact on textile properties.
