Growth responses of the diatom, Cyclotella cryptica (Bacillariophyceae), to gibberellic acid [Algae]

The plant hormone, gibberelic acid (GA), stimulated growth of a marine diatom, C. cryptica Reimann, Lewin and Guillard. Four concentrations of GA (5x, 20x, 25x and 35 x 10 super(-6) g/mL) were added to axenic cultures of C. cryptica . Changes in cell densities, measured by cell counts and turbidimetric reading, confirmed that GA at 20 x 10 super(-6) g/mL produced maximum stimulation. There was an increase in the total number of cells produced and a shorter lag phase of growth at this concentration. Coulter counter measurements of cell size, as well as ocular micrometer measurements, indicated there was no significant variation in cell volumes of GA grown cells over that of the controls.