Effects of Pre-Treatments with Abscisic Acid and/or Benzyladenine on Gas Exchange of French Bean, Sugar Beet, and Maize Leaves During Water Stress and After Rehydration

Net photosynthetic rate (P sub(N)), transpiration rate (E), and stomatal conductance (g sub(s)) during water stress and after rehydration were measured in Phaseolus vulgaris, Beta vulgaris, and Zea mays. Immediately before imposition of water stress by cessation of watering, plants were irrigated with water (control), 100 mu M abscisic acid (ABA), and/or 10 mu M N super(6)-benzyladenine (BA). In all three species, application of ABA decreased g sub(s), E, and P sub(N) already 1 h after application. However, during water stress g sub(s), E, and P sub(N) in plants pre-treated with ABA remained higher than in plants pre-treated with water. Positive effects of ABA application were observed also after rehydration. In contrast, the effects of pre-treatment with BA were species-specific. While in bean plants BA application ameliorated negative effect of water stress, only very slight effects were observed in maize, and in sugar beet BA even aggravated the effects of water stress.