Increased drought resistance induced by pretreatment with abscisic acid in germinating embryos of Haplopappus gracilis

Embryos of Haplopappus gracilis (Nutt.) Gray were prehydrated in water or under different conditions, all of them inhibiting or greatly reducing embryo elongation (abscisic acid, polyethylenglycol, cycloheximide, cordycepin, aminophylline, and at 4°C), dehydrated for 24 h and regerminated. All treatments resulted in improved drought resistance compared with water controls, but the best results were obtained with pretreatment with abscisic acid. In fact these embryos revealed in the rehydration phase, (a) the highest percentage of embryos able to resume germination, (b) the lowest leakage of ninhydrin reacting substances, and (c) the highest level of ¹⁴C-leucine incorporation. Lengthening of the prehydration phase in abscisic acid up to 24–48 h improved the conditions of the embryos in the rehydration phase, with less damage to the cells of the radicle tip. A protective action of abscisic acid, possibly at the level of the cell membrane system, is hypothesized.