Cell Wall Hemicellulose Contributes Significantly to Aluminum Adsorption and Root Growth in Arabidopsis

Abstract

The cell wall (CW) has been recognized as the major target of aluminum (Al) toxicity. However, the components responsible for Al accumulation and the mechanisms of Al-induced CW function disruption are still elusive. The contribution of different CW components (pectin, hemicellulose 1 [HC1], and HC2) to adsorb Al and the effect of Al on xyloglucan endotransglucosylase/ hydrolyase activity were investigated in Arabidopsis (Arabidopsis thaliana) in this study. A fractionation procedure was optimized to effectively extract different CW components, especially to prevent the HC fraction from pectin contamination. When CW materials extracted from Al-treated roots (50 mM Al for 24 h) were fractionated, about 75% of CW Al accumulated in the HC1 fraction. A time-dependent kinetic study showed that only when the HC1 fraction was removed was the amount of Al adsorbed decreased sharply. In vivo localization of xyloglucan endotransglucosylase (XET) activity showed that Al greatly inhibited this enzyme activity within 30 min of exposure, which was concomitant with Al-induced callose deposition in roots. Results from real-time reverse transcription-polymerase chain reaction indicated that three genes may constitute the major contributors to XET activity and that the inhibition of XET activity by Al is caused by transcriptional regulation. These results, to our knowledge for the first time, demonstrate that HC is the major pool for Al accumulation. Furthermore, Al-induced reduction in XET activity could play an important role in Al-induced root growth inhibition.

Interaction of aluminium and drought stress on root growth and crop yield on acid soils

“…Using artificial pectin membranes, Blamey et al (1993) demonstrated that the binding of Al to pectin strongly reduced water permeability of the membranes. Recently, hemicellulose rather than pectins have been implicated in Al binding in CWs (Yang et al 2011a). Further studies in Arabidopsis thaliana (L.) Heynh provided evidence that Al interacts specifically with xyloglucans (Zhu et al 2012).…”

“…Under Al stress, Al strongly binds to the negative charges provided by the carboxylic groups of galacturonic acids of the pectins (Blamey et al 1990;Chang et al 1999) and to hemicellulose (Yang et al 2011a). There is little doubt that the high affinity of Al to the pectic matrix and hemicellulose will substantially affect the chemical and mechanical properties of the CW, and this Al-apoplast interaction has been proposed as the main cause of Al-induced inhibition of root elongation .…”

XTH31, Encoding an in Vitro XEH/XET-Active Enzyme, Regulates Aluminum Sensitivity by Modulating in Vivo XET Action, Cell Wall Xyloglucan Content, and Aluminum Binding Capacity in Arabidopsis

“…For example, the most significant Al-induced change in cell wall components involves the hemicellulose fraction in wheat (Triticum aestivum; Tabuchi and Matsumoto, 2001), triticale (X Triticosecale Wittmack; Liu et al, 2008), and rice (Oryza sativa; Yang et al, 2008), especially in Al-sensitive cultivars. Moreover, we found that in Arabidopsis thaliana, hemicellulose is not only susceptible to Al stress but is also the principal binding site for Al; the amount of Al accumulated in hemicellulose is much more than that in pectin (Yang et al, 2011), although how hemicellulose can bind Al is unclear. Thus, the role of not only pectin but also hemicellulose in Al toxicity/resistance and its underlying physiological and molecular mechanisms need to be further explored.…”

Differential effects of nitrogen forms on cell wall phosphorus remobilization in rice (Oryza sativa) are mediated by nitric oxide, pectin content and the expression of the phosphate transporter OsPT2

“…The extraction of pectin was carried out by washing approximately 2 mg of isolated cell walls three times with 1 mL water at 100°C for 1 h. The supernatants containing pectin were collected in a 5-mL tube after centrifugation at 13,200 rpm for 10 min (Zhong and Läuchli, 1993;Yang et al, 2011).…”