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Balance between nitrogen use efficiency and cadmium tolerance in Brassica napus and Arabidopsis thaliana

Liao, Qiong, Jian, Shao-Fen, Song, Hai-Xing, Guan, Chun-Yun, Lepo, Joe Eugene, Ismail, Abdelbagi M., Zhang, Zhen-Hua
Plant science 2019 v.284 pp. 57-66
Arabidopsis thaliana, Brassica napus, H-transporting ATP synthase, cadmium, energy, gene overexpression, genotype, metal tolerance, mutants, nitrates, nutrient use efficiency, phytoremediation, proton pump, stress response, tonoplast, vacuoles
The transmembrane transport of NO3− and Cd2+ into plant cell vacuoles relies on the energy from their tonoplast proton pumps, V-ATPase and V-PPase. If the activity of these pumps is reduced, it results in less NO3− and Cd2+ being transported into the vacuoles, which contributes to better nitrogen use efficiency (NUE) and lower Cd2+ tolerance in plants. The physiological mechanisms that regulate the balance between NUE and Cd2+ tolerance remain unknown. In our study, two Brassica napus genotypes with differential NUEs, xiangyou 15 and 814, and Atclca-2 mutant and AtCAX4 over-expression line (AtCAX4-OE) of Arabidopsis thaliana, were used to investigate Cd2+ stress responses. We found that the Brassica napus genotype, with higher NUE, was more sensitive to Cd2+ stress. The AtCAX4-OE mutant, with higher Cd2+ vacuolar sequestration capacity (VSC), limited NO3− sequestration into root vacuoles and promoted NUE. Atclca-2 mutants, with decreased NO3− VSC, enhanced Cd2+ sequestration into root vacuoles and conferred greater Cd2+ tolerance than the WT. This may be due to the competition between Cd2+ andNO3− in the vacuoles for the energy provided by V-ATPase and V-PPase. Regulating the balance between Cd2+ and NO3− vacuolar accumulation by inhibiting the activity of CLCa transporter and increasing the activity of CAX4 transporter will simultaneously enhance both the NUE and Cd2+ tolerance of Brassica napus, essential for improving its Cd2+ phytoremediation potential.