Interaction between reactive oxygen species and nitric oxide in drought-induced abscisic acid synthesis in root tips of wheat seedlings

Abscisic acid accumulation and oxidative stress are two common responses of plants to environmental stresses. However, little is known about their rel ationships. The purpose of this article is to investigate the effects of re active oxygen species and nitric oxide on the plant hormone abscisic acid s ynthesis in root tips of wheat (Triticum aestivum L.) seedlings under droug ht stress. Detached root tips were subjected to drought stress by naturally evaporating until 20% of their fresh weights were lost. The activities of superoxide synthases and nitric oxide synthase (EC 1.14.13.39) increased af ter 20 min of treatment and abscisic acid began to accumulate 60 min later. The induction of abscisic acid by drought was strongly blocked by pretreat ing the root tips with reactive oxygen species eliminators tiron or ascorba te acid, and with nitric oxide synthase inhibitor N-omega-nitro-L-arginine or nitric oxide eliminator 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide. Consistent with these results, reactive oxygen species generators diethyldithiocarbamic acid, xanthine-xanthine oxidase and triazole or nitri c oxide donor sodium nitroprusside can also induce abscisic acid accumulati on in root tips of wheat seedlings. While potentiated by reactive oxygen sp ecies, the effect of sodium nitroprusside on abscisic acid accumulation was blocked by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide. Based on these results, we suggest that reactive oxygen species and nitric oxide play important roles in drought-induced abscisic acid synthesis in plant, t hey may be the signals through which the plant can 'sense' the drought cond ition.