Effect of coronatine on stomatal opening in leaves of broadbean and Italian ryegrass.

Sakai et al.1,2) reported that coronatine, a toxin produced by Pseudomonas syringae pv. atropurpurea, induced marked hypertrophy on potato tuber discs, accompanied by rapid disappearance of starch granules. On the other hand, Turner and Graniti3) reported that fusicoccin, a toxin produced by Fusicoccum amygdali, had a physiological activity to enhance stomatal opening. The present work was done to elucidate whether coronatine affects Stomatal opening as one of its functions. Broadbean (Vicia faba, cv. Nintoku) and Italian ryegrass (Lolium multiflorum, cv. Giant) were grown in a green house for 20 days. The discs (1.6cm in diameter) from third leaves of broadbean and the third leaf blades (2cm from the top) of Italian ryegrass were used for this experiment. These samples were placed in Petri dishes and kept in the dark for 1.5hr to make stomata close. The lower surface of these leaf segments were contacted with coronatine solution in a Petri dish and placed in the dark. Distilled water was used as control. After the treatments stomata were replicated on celluloid films after removal of excess water with a filter paper. Twenty five films in each experimental plot were observed under a light microscope. As shown in Fig. 1, stomatal aperture of broadbean was determined by subtracting B from A (A-B),