Effect of Growth Regulators on Stomatal Structure and Development in the Cotyledons of Lagenaria leucantha (Duch.) Rusby

Abstract

In untreated cotyledons (controls) anomocytic stomata and stomata with a single subsidiary cell were observed. In cotyledons treated with growth regulators, anisocytic, paracytic, cyclocytic and several abnormal stomatal types were observed in addition to those found in the controls. Gibberellic acid, though a growth promoter, acted as an inhibitor at high concentration. Ascorbic acid at 25 p.p.m. increased the stomatal index and the size of guard cells, while the stomatal frequency decreased. Sucrose at 2000 p.p.m. increased the stomatal index and the length of guard cells. 2,3,5-Tri-iodobenzoic acid caused degeneration of guard cells and acted as a growth inhibitor at higher concentrations. As the concentration of kinetin increased, decreases in the stomatal frequency, index and size of guard cells were noted. Kinetin also induced the formation of contiguous stomata and the division of guard cells. Sulphanilamide could act either as an inhibitor or as a promoter as its concentration increased. Coumarin at 50 p.p.m. reduced the size of guard cells and the stomatal frequency, and commonly induced persistent stomatal initials, while at 100 p.p.m. only the radicle emerged and the cotyledons failed to emerge from the seed-coat. Increased concentrations of colchicine promoted more induction of persistent stomatal initials, and inhibited stomatal formation as was evidenced by a reduced stomatal frequency and index. Colchicine at 50 p.p.m. induced formation of double pores in a stoma, abnormally large pore sizes, and increases in the size of guard cells and their nuclei. With maleic hydrazide the sizes of guard and epidermal cells were reduced and persistent stomatal initials occasionally formed. Growth promoters could sometimes interact with inhibitors to overcome their inhibitory effect, depending on the substances used in combination and their concentrations.