An Anatomical Investigation into the Effects of Gibberellic Acid on the Expansion of Callitriche Shoots

Abstract

After treatment with gibberellic acid, internodes of floating Oallitriche shoots expand prematurely and achieve greater final lengths than corresponding untreated internodes. Examination of macerated, fully expanded internodes revealed that increased internode lengths could be attributed to increased cell lengths. However, during the early stages of expansion there were increases in the number of mitotic figures and in the number of cells, as revealed in sectioned apices and macerated internodes. Premature expansion was accounted for by increases in both cell length and cell number. Starch loss occurred during expansion, and this was more marked in gibberellic acid-treated tissue. There was an increase in the number of chloroplasts in treated cells. Gibberellic acid did not affect the number of chromosomes observed during division, nor the size of nuclei in mature cells. Binucleate cells were not observed.