Comparison of growth of flacca and wild-type tomato grown under conditions diminishing their differences in stomatal control

The effects of endogenous and exogenous abscisic acid (ABA) on the growth of flacca, a specific ABA-deficient mutant of tomato (Lycopersicon esculentum), and the wild-type variety Rheinlands Ruhm (RR) were investigated under conditions in which the effects of stomatal behavior on growth were minimized. Two experimental systems were used: (1) germination experiments in which the root and hypocotyl lengths were compared and (2) shoot tip culture of in vitro experiments. Flacca had shorter roots and longer hypocotyls than RR and the fresh biomass of plantlets developed from flacca shoot tip culture was greater than that of wild-type plantlets. Low exogenous ABA significantly improved fresh biomass of both plantlets while high exogenous ABA significantly inhibited their growth. It was concluded that endogenous ABA improves root growth and inhibits shoot growth in young tomato seedlings. A low concentration of exogenous ABA tends to improve plant growth while high level of exogenous ABA inhibits plant growth.