Abscisic acid underlies genotypic variation in stomatal responses

Stomata formed at high relative humidity (RH) are less responsive to abscisic acid (ABA), an effect that varies widely between genotypes. Giday et al. study four rose cultivars (Rosa hybrida) grown at 60% and 90% RH and find stomatal responsiveness to desiccation and ABA feeding to be attenuated in two of them at high RH. [ABA] is lower in plants grown at high RH, an effect that is more pronounced in these sensitive cultivars. They determine that the sensitive cultivars undergo a larger decrease in [ABA], rather than having a higher [ABA] threshold for inducing stomatal functioning. However, the cultivar differences in stomatal closure following ABA feeding are not apparent in response to H₂O₂ and downstream elements, indicating that signalling events prior to H₂O₂ generation are involved in the observed genotypic variation.