Exogenous nitric oxide enhances cadmium tolerance of rice by increasing pectin and hemicellulose contents in root cell wall

Abstract

To study the mechanisms of exogenous NO contribution to alleviate the cadmium (Cd) toxicity in rice (Oryza sativa), rice plantlets subjected to 0.2-mM CdCl(2) exposure were treated with different concentrations of sodium nitroprusside (SNP, a NO donor), and Cd toxicity was evaluated by the decreases in plant length, biomass production and chlorophyll content. The results indicated that 0.1 mM SNP alleviated Cd toxicity most obviously. Atomic absorption spectrometry and fluorescence localization showed that treatment with 0.1 mM SNP decreased Cd accumulation in both cell walls and soluble fraction of leaves, although treatment with 0.1 mM SNP increased Cd accumulation in the cell wall of rice roots obviously. Treatment with 0.1 mM SNP in nutrient solution had little effect on the transpiration rate of rice leaves, but this treatment increased pectin and hemicellulose content and decreased cellulose content significantly in the cell walls of rice roots. Based on these results, we conclude that decreased distribution of Cd in the soluble fraction of leaves and roots and increased distribution of Cd in the cell walls of roots are responsible for the NO-induced increase of Cd tolerance in rice. It seems that exogenous NO enhances Cd tolerance of rice by increasing pectin and hemicellulose content in the cell wall of roots, increasing Cd accumulation in root cell wall and decreasing Cd accumulation in soluble fraction of leaves.

Ethylene is involved in root phosphorus remobilization in rice (Oryza sativa) by regulating cell-wall pectin and enhancing phosphate translocation to shoots

“…Pectin has been demonstrated to be a key intermediate material in cell-wall P re-utilization, and it responds to multiple environmental stimuli. For instance, Yang et al (2008) and Xiong et al (2009) found that exposure of rice to Al and Cd led to an increment of pectin content in root. Yang et al (2010) reported that osmotic stress inhibited Al accumulation in root apices of the Al-sensitive genotype VAX1, an effect that was attributed to a lower cell-wall pectin content and its degree of methylation.…”

Cadmium toxicity

“…39 Xiong et al concluded that decreased distribution of cadmium in the soluble fraction of leaves and roots and increased distribution of cadmium in the cell walls of roots were responsible for the nitrogen monoxide-induced increase of cadmium tolerance in rice. 40 Excessive lignin production induced by cadmium accounted for the solidification of cell wall and subsequent restriction of root growth. 41 The distribution of de-esterified and esterified pectins on the radical apex differed with different concentrations of cadmium, indicating that cadmium spatially modulates the synthesis and distribution of both pectins.…”

The cell wall in plant cell response to trace metals: polysaccharide remodeling and its role in defense strategy

“…Lead can be identified by optical microscopy, e.g., by rhodizonic acid that forms red complexes with this metal (Tung and Temple 1996). Cadmium may be identified, e.g., by Leadmium reagent (Xiong et al 2009) in fluorescence and confocal microscopy. Aluminum is often stained with, e.g., morin (unbound, free Al ions; Eticha et al 2005a) and lumogallion (Silva et al 2000), the fluorochromes also used for fluorescence and confocal microscopy.…”