Changes of photosynthesis under blue light were examined in the ABA-overproducing 7B-1 mutant in tomato. Net photosynthetic rate (PN), stomatal conductance (gs), intrinsic water-use efficiency (WUEi) and chlorophyll (a+b) [Chl (a+b)] content in leaves of different insertion (1st, 4th and 9th ones) were measured in 5-, 7- and 9-week-old plants. PN, gs, and Chl (a+b) content were mostly similar in young leaves of 7B-1 and wild type (WT) plants. With the aging of leaves, a blue-light-induced increase in PN and gs to steady-state was delayed and steady-state values of PN and gs were lower in 7B-1 plants compared with WT. Steady-state values of WUEi were increased in 4th and 9th leaves of 7B-1 plants compared with WT. The results can be explained by the higher endogenous level of ABA in 7B-1 plants and their lower sensitivity to ABA in earlier growth stage., E. Ježilová ... [et al.]., and Obsahuje bibliografii