Mechanism Enhancing Arabidopsis Resistance to Cadmium: The Role of and Proton Pump.

Heavy metal pollution is serious in China, and abscisic acid (ABA) is an important stress hormone. How it regulates plant tolerance to cadmium remains unclear, so we aimed to explore the molecular mechanism responsible for enhanced cadmium resistance in Arabidopsis wild-type and mutant plants and seedlings. Arabidopsis/ were cultured hydroponically for 28/15 days and then treated with 20/10 μM Cd/Cd+ABA (5 μM) for 3/4 days. Chlorophyll degradation rate, SPAD values, proline, MDA, ABA, , and Cd concentrations were measured in root vacuoles and protoplasts; root to shoot and Cd concentration ratios were determined and , and related gene expression was studied. Cytoplasmic ABA levels in root cells of and Arabidopsis mutants were significantly lower than those in the wild-type, apparently making the latter more resistant to Cd. long-distance transporter responded to ABA signaling by downregulating its own expression, while did not respond. Concomitantly, proton pump activity in wild-type plants was higher than in the and mutants; thus, more and Cd accumulated in the vacuoles of wild-type root cells. ABA application inhibited Cd absorption by . responded to exogenous ABA signal by downregulating its own expression, while the lack of response by resulted in increased amount of accumulating in the roots to participate in the anti-cadmium reaction. responds to the ABA signal to inhibit its own expression, whereas unresponsiveness of causes accumulation of in the roots; thus, enhancing Cd resistance. In Arabidopsis, because of proton pump action, more and Cd accumulate in the vacuoles of Arabidopsis root cells, thereby reducing damage by Cd toxicity. However, in , the addition of exogenous ABA inhibited Cd absorption. Our data provide a sound basis to the theoretical molecular mechanism involved in hormone signaling during response of plants to heavy metal stress.