Fusicoccin inhibits dark-induced stomatal closure by reducing nitric oxide in the guard cells of broad bean

By using pharmacological approaches and laser scanning confocal microscopy based on 4,5-diaminofluorescein diacetate (DAF-2DA), the relationship between the inhibition of dark-induced stomatal closure caused by fusicoccin (FC) and the changes of nitric oxide (NO) levels in guard cells in broad bean was studied. The results show that, like 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), a NO scavenger and N-G-nitro-L-Arg-methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), FC inhibited stomatal closure induced by darkness, and reduced the levels of NO in guard cells in darkness, indicating that FC inhibits dark-induced stomatal closure through lessening NO levels in guard cells. In addition, similar to c-PTIO, both FC and butyric acid not only suppressed sodium nitroprusside (SNP)-induced stomatal closure and DAF-2DA fluorescence in guard cells, but also reopened the closed stomata induced by dark and removed NO that had been generated by dark. The results show that both FC and butyric acid cause NO removal in guard cells, and also suggest that FC-caused NO removal is probably associated with cytosolic acidification in guard cells. Taken together, our results show that FC perhaps causes cytosolic acidification in guard cells, consequently induces NO removal and reduces NO levels in guard cells, and finally inhibits stomatal closure induced by dark.