Aluminum-inhibited root growth of rice seedlings is mediated through putrescine accumulation

Abstract

The effects of AlCl3 on growth and polyamine levels of rice roots were investigated. When rice roots were treated with AlCl3, root growth was markedly inhibited. AlCl3 treatment resulted in a higher putrescine content and lower spermidine and spermine contents in rice roots. d-Argnine and α-methylornithine, inhibitors of putrescine biosynthesis, caused a reduced content of putrescine in rice roots under Al stress. AlCl3 treatment also resulted in a decrease in diamine oxidase activity in rice roots. The growth of rice roots in the presence of AlCl3 was recovered after the addition of d-arginine or α-methylornithine. The protective effect of d-arginine or α-methylornithine in counteracting AlCl3-inhibited growth of rice roots is unlikely caused by reduction of Al uptake. Furthermore, the effect of the growth recovery in AlCl3-treated rice roots by d-arginine or α-methylornithine was reversed by the addition of putrescine. Our results strongly suggest that putrescine accumulation is a factor causing growth inhibition of rice roots under Al tress. Evidence is also presented to show that lignification is responsible for putrescine- and AlCl3-inhibited growth of rice roots.