Sulfur-Mediated-Alleviation of Aluminum-Toxicity in Citrus grandis Seedlings.

Li-Song Chen,Huan-Huan Chen,Peng Guo,Xin Ye,Yi-Ping Qi,Qiang Li,Lin-Tong Yang

doi:10.3390/ijms18122570

Abstract

Limited data are available on the sulfur (S)-mediated-alleviation of aluminum (Al)-toxicity in higher plants. Citrus grandis seedlings were irrigated for 18 weeks with 0.5 mM MgSO4 or 0.5 mM MgSO4 + 0.5 mM Na2SO4, and 0 (−Al) or 1 mM AlCl3·6H2O (+Al, Al-toxicity). Under Al-toxicity, S decreased the level of Al in leaves; increased the relative water content (RWC) of roots and leaves, the contents of phosphorus (P), calcium (Ca) and magnesium (Mg) per plant, the dry weights (DW) of roots and shoots, the ratios of root DW/shoot DW, and the Al-induced secretion of citrate from root; and alleviated the Al-induced inhibition of photosynthesis via mitigating the Al-induced decrease of electron transport capacity resulting from the impaired photosynthetic electron transport chain. In addition to decreasing the Al-stimulated H2O2 production, the S-induced upregulation of both S metabolism-related enzymes and antioxidant enzymes also contributed to the S-mediated-alleviation of oxidative damage in Al-treated roots and leaves. Decreased transport of Al from roots to shoots and relatively little accumulation of Al in leaves, and increased leaf and root RWC and P, Ca, and Mg contents per plant might also play a role in the S-mediated-alleviation of Al-toxicity.

Highlights

Aluminum (Al) exists mainly as the forms of insoluble deposits when soil is neutral or mildly acidic, but is released from these deposits into soil solution when soil has a pH < 5.0
These results indicated that S alleviated the Al-induced inhibition of growth
We found that the Al-induced decreases in seedling growth, leaf CO2 assimilation, and pigments, and alterations of leaf OJIP transients and fluorescence parameters were more pronounced at 0.5 mM S than those at 1 mM S (Figure 1, Figure 3 and Figures S1–S4), demonstrating that S alleviated Al-toxicity in C. grandis seedlings

Summary

Introduction

Aluminum (Al) exists mainly as the forms of insoluble deposits when soil is neutral or mildly acidic, but is released from these deposits into soil solution when soil has a pH < 5.0. Plants survive in acidic soils with high levels of active Al via two main mechanisms of Al detoxifications: (a) external detoxification, including the Al-induced release of organic acid (OA) anions from roots; and (b) internal detoxification [5,6,7,8]. Al-toxicity can cause the accumulation of reactive oxygen species (ROS), leading to peroxidation of proteins and membrane lipids in plant cells. The Al-sensitive sorghum line displayed higher ROS levels in the root tips than the Al-tolerant line did [17]. More antioxidant enzymes were induced to higher levels in the Al-tolerant sorghum line than those in the Al-sensitive line root tips [15]. Genes involved in ROS scavenging were upregulated by Al-toxicity in C. sinensis and C. grandis roots, especially in C. sinensis roots [20]

Methods

Results

Discussion

Conclusion