Physiological and molecular responses of broad bean (Vicia faba L.) to aluminum stress

In this study, the responses of broad bean cultivars resistant (YD) and sensitive (AD) to aluminum (Al) stress were investigated at physiological and molecular levels. The results showed that Al induced more citrate exudation in YD roots than that in AD roots, suggesting that citrate exudation is involved in broad bean Al resistance. The analyses for oxidative stress levels and antioxidant enzyme activities indicated that YD had a strong ability to cope with the oxidative stress induced by Al. To investigate the molecular responses of broad bean to Al stress further, a forward suppression subtractive hybridization cDNA library was constructed to identify Al-responsive genes in YD roots treated with 50-mu M Al for a 24-h period. Of the obtained 162 high-quality ESTs, genes related to antioxidant enzymes including copper-zinc superoxide dismutase (SOD), class III peroxidase (POD) and germin-like protein (GEP) were up-regulated. Higher transcription levels of SOD and POD were observed in YD but not in AD roots, which is in agreement with the enhanced activities of antioxidant enzymes in YD roots under Al stress conditions. Furthermore, the up-regulated expression of vha2, encoding a plasma membrane (PM) H+-ATPase, and 14-3-3b in YD roots under Al stress were also detected and confirmed by RT-PCR analysis. Western and immunoprecipitation analyses indicated that Al-enhanced expressions and interactions of the PM H+-ATPase and 14-3-3 proteins might be involved in the regulation of citrate secretion in YD roots under Al stress.