Molecular mechanism for cadmium-induced anthocyanin accumulation in Azolla imbricata

Anthocyanins inducibly synthesized by Cd treatment showed high antioxidant activity and might be involved in internal detoxification mechanisms of Azolla imbricata against Cd toxicity. In order to understand anthocyanin biosynthesis mechanism during Cd stress, the cDNAs encoding chalcone synthase (CHS) and dihydroflavonol reductase (DFR), two key enzymes in the anthocyanin synthesis pathway, were isolated from A. imbricata. Deduced amino acid sequences of the cDNAs showed high homology to the sequences from other plants. Expression of AiDFR, and to a lesser extent AiCHS, was significantly induced in Cd treatment plant in comparison with the control. CHS and DFR enzymatic activities showed similar pattern changes with these genes expression during Cd stress. These results strongly indicate that Cd induced anthocyanin accumulation is probably mediated by up-regulation of structural genes including CHS and DFR, which might further increase the activities of enzymes encoded by these structural genes that control the anthocyanin biosynthetic steps.     

Anthocyanins and tannins in ozone-fumigated guava trees

Psidium guajava “Paluma”, a tropical tree species, is known to be an efficient ozone indicator in tropical countries. When exposed to ozone, this species displays a characteristic leaf injury identified by inter-veinal red stippling on adaxial leaf surfaces. Following 30 days of three ozone treatments consisting of carbon filtered air (CF – AOT40 = 17 ppb h), ambient non-filtered air (NF – AOT40 = 542 ppb h) and ambient non-filtered air + 40 ppb ozone (NF + O₃ – AOT40 = 7802 ppb h), the amounts of residual anthocyanins and tannins present in 10 P. guajava (“Paluma”) saplings were quantified. Higher amounts of anthocyanins were found in the NF + O₃ treatment (1.6%) when compared to the CF (0.97%) and NF (1.30%) (p < 0.05), and of total tannins in the NF + O₃ treatment (0.16%) compared to the CF (0.14%). Condensed tannins showed the same tendency as enhanced amounts. Regression analyses using amounts of tannins and anthocyanins, AOT40 and the leaf injury index (LII), showed a correlation between the leaf injury index and quantities of anthocyanins and total tannins. These results are in accordance with the association between the incidence of red-stippled leaves and ozone polluted environments.