The Role Of Nitric Oxide In Toxicity Of Hibiscus Moscheutos To Aluminum

Aluminum (Al) is the most abundant metal element in the Earth crust. Al becomes a major factor limiting crop growth and yield when solubilized in acid soils to phytotoxic species Al3+, but the mechanism underlying the Al toxicity remains largely unknown. There has been no report on effect of Al toxicity on growth of Hibiscus moscheuto. To study tolerance of H. moscheutos that is an herbaceous perennial horticultural plant to Al, effect of AlCl3 on seed germination and root elongation of H. moscheutos was studied using hydroponic culture, and compared with that of Al on two wheat genotypes differing in Al tolerance. Nitric oxide (NO) has emerged as an important signaling molecule that modulates numerous physiological processes in plants. To evaluate the role of NO in Al toxicity in H. moscheutos, effects of NO donor (sodium nitroprusside, SNP) and scavenger (2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxied, cPTIO) and nitric oxide synthase (NOS) inhibitor (nitro-L-arginine, L-NNA) on root elongation in the presence and absence of Al were investigated. Main findings in the present study were as follows:1. Seed germination of H. moscheutos and two wheat genotypes was insensitive to AlCl3 up to 500μmol/L when exposed to Al3+ for 24 h.2. AlCl3 at 50μmol/L significantly inhibited elongation of primary and lateral root of H. moscheutos. There was a greater inhibition of lateral root elongation by AlCl3 than that of primary roots. The number of lateral root in H. moscheutos and two wheat genotypes was relatively insensitive to AlCl3. When treated with 50μmol/L AlCl3 for 48 hours, roots biomass of the two wheat genotypes decreased significantly, but the roots biomass of H. moscheutos was not affected, suggesting that seedlings of H. moscheutos could be more tolerant to Al than those of the two wheat genotypes.3. Seed germination of H. moscheutos was enhanced by NO donor SNP at concentration of 100μmol/L. There were increases in lateral root elongation and numbers of lateral roots when H. moscheutos was treated with SNP at concentration less than 500μmol/L, but the same treatment led to a substantial inhibition of primary root elongation. SNP at concentration of 500μmol/L inhibited elongation of both primary and lateral roots.