Cytokinin‐ and auxin‐induced stomatal opening is related to the change of nitric oxide levels in guard cells in broad bean

Abstract

The relationship between cytokinin‐ and auxin‐induced stomatal opening and nitric oxide (NO) levels in guard cells in broad bean was studied. Results indicate that cytokinins and auxins reduced the levels of NO in guard cells and induced stomatal opening in darkness. In addition, cytokinins not only reduced NO levels in guard cells caused by sodium nitroprusside (SNP) in light but also abolished NO that had been generated by dark, and then promoted the closed stomata reopening, as did NO scavenger 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide. However, unlike cytokinins, auxins not only had incapability to reduce NO levels by SNP but also could not abolish NO having been generated by dark, so auxins could not promote the closed stomata to reopen. The above‐mentioned effects of auxins were similar to that of nitric oxide synthase (enzyme commission 1.14.13.39) inhibitor NG‐nitro‐l‐Arg‐methyl ester. Hence, it is concluded that cytokinins reduced probably the levels of NO in guard cells via scavenging, and auxins reduced NO levels through restraining NO generation in all probability, and then induced stomatal opening in darkness.