NO-RELEASING SUBSTANCES THAT INDUCE GROWTH ELONGATION IN MAIZE ROOT SEGMENTS

Root segments of maize were incubated in different solutions containin g substances that non-enzymatically release nitric oxide, such as sodi um nitrite (SN), sodium nitroprusside (SNP), nitrosoglutathione (NGLU) and nitrosocysteine (NCYS). We found that all of these substances ind uced root tip expansion in a dose-dependent manner. The decreasing ord er 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. Ni tric oxide scavenger such as methylene blue prevented the elongation i nduced by NO-releasing substances, but had no effect on indole-3-aceti c acid (IAA)-induced cell expansion. Our results suggest that nitric o xide is the putative elongation inducer and that IAA and NO-releasing substances conceivably share common steps in the signal transduction p athway, since both elicited the same plant response. Vanadate, a plasm amembrane ATPase inhibitor, significantly reversed IAA-induced elongat ion when supplied at 10 mu M concentration. IAA-induced elongation was strongly enhanced by 10 nM BAY K 8644, an agonist of voltage dependen t Ca2+ channels. Promotion of root elongation in the absence of IAA oc curred 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 p lasmamembrane.