Seed pre-treatment using a derivative of 5-hydroxybenzimidazole (AMBIOL) pre-acclimates carrot seedlings to drought

The possibility that AMBIOL, a derivative of 5-hydroxybenzimidazole, may promote drought acclimation of carrot seedlings was studied. Carrot seeds were pre-treated by soaking in AMBIOL solutions of 0, 0.1, 1 or 10 mg L–1 for 24 h and germinated. Fifteen-day-old seedlings were exposed to a 7-d drought by withholding water until soil moisture content declined to one-third of the initial values. Drought caused a significant reduction in xylem pressure potential, elongation growth, leaf area expansion, root growth and dry matter production. Membrane capacitance, net photosynthesis, stomatal conductance, transpiration and water use efficiency all declined in all plants under drought. However, seed pre-treatment using AMBIOL 0.1 and 10 mg L–1 completely alleviated the drought-induced reduction in shoot dry matter production. Seed preconditioning using AMBIOL 10 mg L–1 promoted dry matter production, which was 214% higher than in the untreated droughted plants and was even 26% higher than that of the untreated, unstressed controls. AMBIOL appeared to have induced drought acclimation through root adjustments that enhanced root growth, possibly supplying root-derived essential factors. Key words: Acclimation, antioxidant, carrot, drought, dry matter production, 5-hydroxybenzimidazole, growth, membrane capacitance