Higher Aluminum Tolerance of <i>Lespedeza bicolor</i> Relative to <i>Lespedeza cuneata</i> Is Associated with Saccharide Components of Root Tips
Qing-Bin Sun | Chun-Qin Yin | Han Zheng | Xiao-Ying Dong | Ren-Fang Shen | Xue-Qiang Zhao
Aluminum (Al) toxicity is the primary factor limiting agricultural productivity in acid soils. The cell wall is mainly composed of saccharides and the first barrier for aluminum (Al) to enter plant root cells, but it is unknown whether and how root saccharide components are involved in regulating the Al tolerance of <i>Lespedeza</i> that is well adapted to acid soils. Here, we used Al-tolerant <i>Lespedeza bicolor</i> and Al-sensitive <i>Lespedeza cuneata</i> to examine the association of root saccharide components with <i>Lespedeza</i> Al tolerance through analyzing the saccharide changes of roots exposed to Al toxicity. Al-sensitive <i>Lespedeza</i> accumulated more Al and pectin but less hemicellulose in the root cell walls than Al-tolerant <i>Lespedeza</i>. Al treatment decreased the amounts of total sugar secreted from and within the roots of only Al-tolerant <i>Lespedeza</i>. Al treatment decreased the content of root monosaccharides including glucose and mannose in both <i>Lespedeza</i> species, but increased the xylose contents in only Al-sensitive <i>Lespedeza</i>. Taken together, less cell wall pectin rather than hemicellulose is responsible for less root Al accumulation, and Al-decreased root saccharide contents may enhance root organic-acid secretion to chelate toxic Al, both of which contribute to <i>Lespedeza</i> Al tolerance.
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