Effects of the Dark Septate Endophyte (DSE) Exophiala pisciphila on the Growth of Root Cell Wall Polysaccharides and the Cadmium Content of Zea mays L. under Cadmium Stress

This paper aims to investigate the mechanism by which dark septate endophytes (DSEs) enhance cadmium (Cd) tolerance in there host plants. Maize (Zea mays L.) was inoculated with a DSE, Exophiala pisciphila, under Cd stress at different concentrations (0, 5, 10, and 20 mg·kg−1). The results show that, under 20 mg/kg Cd stress, DSE significantly increased maize biomass and plant height, indicating that DSE colonization can be utilized to increase the Cd tolerance of host plants. More Cd was retained in DSE-inoculated roots, especially that fixed in the root cell wall (RCW). The capability of DSE to induce a higher Cd holding capacity in the RCW is caused by modulation of the total sugar and uronic acid of DSE-colonized RCW, mainly the pectin and hemicellulose fractions. The fourier-transform spectroscopy analysis results show that carboxyl, hydroxyl, and acidic groups are involved in Cd retention in the DSE-inoculated RCW. The promotion of the growth of maize and improvement in its tolerance to Cd due to DSEs are related to restriction of the translocation of Cd from roots to shoots; resistance of Cd uptake Cd inside cells; and the increase in RCW-integrated Cd through modulating RCW polysaccharide components.

Regulatory Mechanism of Copper Oxide Nanoparticles on Uptake of Different Species of Arsenic in Rice

Copper oxide nanoparticles (CuO NPs) are widely used as a fungicide in agriculture. The application of CuO NPs in agriculture affects the growth of rice and metal accumulation in rice. However, the mechanism of CuO NPs on arsenic (As) accumulation in rice remains unclear. In this study, a hydroponic culture was produced to investigate the mechanism of the effect of 50 and 100 mg L−1 CuO NPs on As accumulation in rice. Our results showed that CuO NPs decreased As(III/V) accumulation in the roots and shoots by adsorbing As(III/V), oxidizing of As(III) on the surface, and thickening the root cell wall. The addition of CuO NPs regulated the expression of the OsNIP1;1, OsHAC1;1, and OsHAC4 genes, which decreased As(III) transport and promoted As(V) reduction in the roots. Moreover, when CuO NPs were co-exposed to As, a negative correlation between the concentration of Cu and As in rice was also found in our study. However, CuO NPs significantly increased Cu accumulation in rice and constrained the rice growth. In conclusion, CuO NPs might be a promising way to decrease As accumulation in rice, but the negative effects such as growth inhibition should be further considered. Therefore, the application of CuO NPs in rice plants should take a more restrained approach.

The Aluminum Distribution and Translocation in Two Citrus Species Differing in Aluminum Tolerance

Background: Many citrus orchards of south China suffer from soil acidification, which induced aluminum (Al) toxicity. The Al-immobilization in vivo is crucial for Al detoxification. However, the distribution and translocation of excess Al in citrus species were not well illustrated.Results: The seedlings of ‘Xuegan’ [Citrus sinensis (L.) Osbeck] and ‘Shatianyou’ [Citrus grandis (L.) Osbeck] that differed in Al tolerance were hydroponically treated with nutrient solution (Control) or supplemented by 1.0 mM Al3+ (Al toxicity) for 21 days after three months of pre-culture. The Al distribution at the tissue level of citrus species following the order: lateral roots > primary roots > leaves > stems. The fragmentation of fresh lateral roots revealed the ratio of Al distribution at the cell wall, cell organelle and cytoplasmic supernatant was about 8:2:1 of two citrus species under Al stress. Besides, the Al distribution at the lateral root cell wall components suggested the pectin is the most Al-accumulating site in citrus species. Compared to C. grandis, C. sinensis had a significantly higher Al concentration on the cell wall of lateral roots whereas remarkably lower Al levels on the leaves and stems. Furthermore, the Al translocation revealed by the absorption kinetics of the cell wall demonstrated that C. sinensis had a higher Al retention and stronger Al affinity on the root cell wall than C. grandis. According to the FTIR (Fourier transform infrared spectroscopy) analysis, the Al distribution and translocation might be affected by modifying the structure and components of the citrus lateral root cell wall. Conclusions: A higher Al-retention, mainly targeted by the pectin of the root cell wall, and a lower Al translocation efficiency from roots to shoots contributed to a higher Al tolerance of C. sinensis than C. grandis.