NO-releasing substances that induce growth elongation in maize root segments

Root segments of maize were incubated in different solutions containing substances that non-enzymatically release nitric oxide, such as sodium nitrite (SN), sodium nitroprusside (SNP), nitrosoglutathione (NGLU) and nitrosocysteine (NCYS). We found that all of these substances induced root tip expansion in a dose-dependent manner. The decreasing order of potency for root-induced elongation was: 10(-7) M SN, pH 4.5; 10(-11) M NCYS, 10(-10) M SNP, 10(-9) M NGLU and 10(-7) M SN, pH 7.0. Nitric oxide scavenger such as methylene blue prevented the elongation induced by NO-releasing substances, but had no effect on indole-3-acetic acid (IAA)-induced cell expansion. Our results suggest that nitric oxide is the putative elongation inducer and that IAA and NO-releasing substances conceivably share common steps in the signal transduction pathway, since both elicited the same plant response. Vanadate, a plasmamembrane ATPase inhibitor, significantly reversed IAA-induced elongation when supplied at 10 mu M concentration. IAA-induced elongation was strongly enhanced by 10 nM BAY K 8644, an agonist of voltage dependent Ca2+ channels. Promotion of root elongation in the absence of IAA occurred only at higher concentrations of BAY K; Vanadate and BAY K had no influence on the NCYS-induced elongation suggesting that the common steps in the signalling of IAA and NCYS are not at the level of the plasmamembrane.