Gibberellic Acid Induced Changes in the Ultrastructure of Chloroplasts and the Content of Chlorophyll in Leaves of Dwarf Maize (Zea mays L.)

Abstract

Summary Water culture experiments with a complete nutrient solution were conducted to investigate the effect of GA 3 -treatment on the ultrastructure and the pigment content in the 3rd leaf blade of dwarf maize. Tall maize was also included for comparison. It was found that dwarfism in maize was nearly without effect on the ultrastructure and the pigment content of chloroplasts. GA 3 induced an absolute decrease in the total chlorophyll content in the leaves of dwarf plants. The ultrastructure of both mesophyll and bundle sheath chloroplasts of GA 3 -treated dwarf plants was markedly changed. In mesophyll chloroplasts, the grana and stroma thylakoids were swollen and showed a certain degree of desorientation. A great number of osmiophilic granules were scattered between the swollen thylakoids. The chloroplasts in the bundle sheath cells differed in their sensitivity to GA 3 . Some of them were deformed and quite irregular in shape and showed a great number of osmiophilic granules and large vacuoles. Other chloroplasts exhibited well-developed small grana and small starch grains. Chloroplasts with normal structure were also found. The observed effects of GA 3 -treatment on the ultrastructure of plastids are not primary effects of the growth substances. The interrelationships between GA 3 -treatment, structure of chloroplasts and calcium content will be discussed.