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Cell wall components such as pectin and hemicelluloses have been proposed to be involved in aluminum resistance mechanisms in plants. However, whether hydroxyproline-rich glycoproteins (HRGPs), one of the most abundant proteins of the cell walls, are involved in Al resistance mechanisms remains elusive. In this study, two rice cultivars Xiushui 03 (Al resistant) and Xiushui 128 (Al sensitive) significantly differing in Al resistance were identified. In the absence of Al, no significant difference was observed in contents of glycoproteins and hydroxyproline in cell wall fractions of these two cultivars. At the early stage of Al toxicity, glycoproteins and hydroxyproline were significantly induced in these two cultivars, but levels of their accumulation in cell walls were much higher in cv. Xiushui 03 than in cv. Xiushui 128. At the late stage of Al toxicity, their accumulation in cell walls dramatically decreased in cv. Xiushui 128 and, however, still kept a high level in cv. Xiushui 03. The finding that Al-induced changes of glycoproteins and hydroxyproline were completely consistent indicates that Al-induced glycoproteins are HRGPs. Further observation utilizing transmission electron microscope showed that HRGPs were greatly accumulated in cell walls leading to thickening of cell walls in cv. Xiushui 03, however, HRGPs and cell walls greatly decreased in cv. Xiushui 128. These data suggest that Al-induced HRGP accumulation in cell walls is involved in alleviating Al toxicity in rice.

BackgroundThe calcineurin B-like protein (CBL) and CBL-interacting protein kinase (CIPK) signaling system plays a key regulatory role in plant stress signaling. The roles of plant-specific CIPKs, essential for CBL-CIPK functions, in the response to various abiotic stresses have been extensively studied so far. However, until now, the possible roles of the CIPKs in the plant response to heavy metal toxicities are largely unknown.ResultsIn this study, we used bioinformatic and molecular strategies to isolate 12 HsCIPK genes in Tibetan Plateau annual wild barley (Hordeum spontaneum C. Koch) and subsequently identified their functional roles in the response to heavy metal toxicities. The results showed that multiple HsCIPKs were transcriptionally regulated by heavy metal toxicities (e.g., Hg, Cd, Cr, Pb, and Cu) and other abiotic stresses (e.g., salt, drought, aluminum, low and high temperature, and abscisic acid). Furthermore, the ectopic overexpression of each HsCIPK in rice (Oryza sativa L. cv Nipponbare) showed that transgenic plants of multiple HsCIPKs displayed enhanced tolerance of root growth to heavy metal toxicities (Hg, Cd, Cr, and Cu), salt and drought stresses. These results suggest that HsCIPKs are involved in the response to heavy metal toxicities and other abiotic stresses.ConclusionsTibetan Plateau annual wild barley HsCIPKs possess broad applications in genetically engineering of rice with tolerance to heavy metal toxicities and other abiotic stresses.Electronic supplementary materialThe online version of this article (10.1186/s12284-018-0242-1) contains supplementary material, which is available to authorized users.

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The yield of ˙OH and oxidation of pollutants by biochar/H2O2 were enhanced dramatically by trace dissolved Fe(iii).