Sequestration of Mn into the cell wall contributes to Mn tolerance in sugarcane (Saccharum officinarum L.)

Abstract

Sugarcane (Saccharum officinarum L.) grown on acid soils suffers serious chlorosis resulting from excess manganese (Mn). We explored the mechanisms underlying sugarcane tolerance to excess Mn. Seedlings of genotypes YC96–66 (66) and YC58–21 (21) were cultured hydroponically with MnCl2, then Mn effects on leaf chlorophyll concentration, Mn subcellular distribution, cell wall polysaccharides were determined. A Mn adsorption kinetics assay was also conducted to examine the association of Mn-induced pectin modification with Mn-binding to cell walls. Excess Mn caused significant dose- and time-dependent decrease in chlorophyll, with serious chlorosis in genotype 21 compared to 66. Genotype 66 absorbed more Mn and maintained higher leaf Mn, with greater proportions of Mn retained in cell walls. Up to 93.2% and 90.0% of cell wall-bound Mn was found in the pectin fraction in genotype 66 and 21, respectively. Mn induced pectin accumulation and pectin methylesterase activation, along with a decrease in the degree of pectin methylesterification, which thereby enhanced cell wall Mn-binding capacity in genotype 66. In contrast, no remarkable change was observed in genotype 21. Mn-induced pectin accumulation, pectin demethylesterification and subsequent sequestration of Mn into the cell wall contribute to Mn tolerance in the sugarcane.