Effect of Gibberellic Acid on Cell Division and Cell Elongation in Anthers of the Gibberellin Deficient gib‐1 Mutant of Tomato

Analysis of flower development in the gibberellin (GA) deficient gib‐1 tomato mutant showed that while flower development is arrested the anther growth slowed down unless GA was applied. Northern blot analyses showed that treatment with GA3 enhanced the expression of genes which are correlated with DNA replication (histones h1 and h2b) and cell elongation (expansin and α‐tubulin). In anthers, at developmental arrest, cell elongation was affected in the tapetum, pollen mother cells and epidermal cells. Elongation was significantly less in the longitudinal direction, while in the transverse direction outer tapetum and pollen mother cells were also smaller. Except for the outer tapetum, the cell numbers were the same as in wild‐type tomato, indicating that cell division was less influenced. Scanning electron microscopy revealed that on the lateral surface of gib‐1 anthers the epidermal cells that were affected in their elongation due to GA deficiency did not differentiate into interlocking hairs. Induction of hair development, of which the timing was similar to wild type, occurred after treatment with GA3, GA1, GA4 and GA9, while GA20 was less effective. Analysis of the in situ localization of expansin and histone h2b transcripts in gib‐1 anthers after GA3 treatment revealed that the increased mRNA accumulation was predominantly localized in the cells that were less elongated compared to wild‐type cells. The consequence of reduced cell elongation due to GA deficiency on anther development is discussed.