Cadmium-tolerance of transgenic Ipomoea aquatica expressing serine acetyltransferase and cysteine synthase

Abstract

Ipomoea aquatica (water spinach) is a common aquatic plant growing in lakes and wetlands in Southeast Asia. Due to its vigorous growth, they were considered to be potentially useful for remediation of polluted water with, for example, high sulfate and heavy metals. In previous studies, we successfully constructed transgenic I. aquatica plants, which simultaneously expressed two genes encoding serine acetyltransferase and cysteine synthase involved in sulfate assimilation pathways. Resulting transgenic plants were shown to rapidly grow and to accumulate sulfate at a high level. In the present study, we tested the effect of cadmium on their physiological and biochemical features. Upon hydroponical cultivation in the presence of 200 mM cadmium for 7 days, two transgenic lines (SR1 and SR2) accumulated 2- to 4-fold higher levels of cysteine and glutathione than the wild type control plants. When plantlets were exposed to 100 mM cadmium for 30 days, wild type and transgenic SR2 plantlets died, or growth was greatly retarded with reduced biomass, whereas transgenic SR1 exhibited a 1.7-fold increase in total biomass in comparison with the initial weight at day-0 of cadmium treatment. These results suggested that some transgenic plants expressing serine acetyltransferase and cysteine synthase could mitigate detrimental effects of cadmium toxicity, perhaps by efficiently producing and accumulating sulfuric compounds.