Different abscisic acid‐deficient mutants show unique morphological and hydraulic responses to high air humidity

High relative humidity (RH) perturbs plant growth, stomatal functioning and abscisic acid (ABA) homeostasis, but the role of ABA in this physiological regulation is equivocal. To determine role(s) responses to high RH, wild-type (WT) tomato barley plants their respective ABA-deficient mutants flacca Az34 (which are mutated same locus biosynthesis pathway) were grown contrasting RHs (60% 90%) measure biomass partitioning, traits water relations. Surprisingly, growth RH did not affect foliar levels either species. While showed similar size density as WT plants, had larger more abundant stomata. increased tomato, decreased it barley, barley. Altered little effect on photosynthesis, lower photosynthesis. deficiency shoot rate (RGRSHOOT) both species, yet was counteracted by increasing leaf status RGRSHOOT flacca, tomatoes, while having no affecting net assimilation rate, area ratio (LAR) specific an ABA-dependent manner. ABA-RH interaction affected development only. Thus, different crop species show variable deficiency, making difficult generalise at RHs.