Hyper-assimilation of sulfate and tolerance to sulfide and cadmium in transgenic water spinach expressing an Arabidopsis adenosine phosphosulfate reductase

Adenosine phosphosulfate (APS) reductase is one of key enzymes in the sulfur assimilation pathway in higher plants, catalyzing the formation of adenosine 5′-phosphosulfate from sulfate and ATP. In order to improve sulfur uptake capacity of water spinach (Ipomea aquatica), a plant which commonly grows wild in Southern Asia and has good potential for sequestration of environmental pollutants like sulfuric compounds, an Arabidopsis gene (APR1), encoding a plastid-resident APS reductase, was introduced into cut cotyledons via Agrobacterium-mediated transformation. Among 267 regenerated shoots initially obtained from 2,119 cotyledon explants, two were found to efficiently express the introduced gene and could be grown to maturity. APS reductase activity in leaves was estimated to be over 2-fold the wild-type level. Upon cultivation in the presence of 2 mM sodium sulfate, a 2.5-fold higher sulfate uptake was observed in comparison with wild-type plants. When grown in the presence of toxic levels of sulfide or cadmium, they showed a higher tolerance with increased fresh weight as compared with controls. These results suggest that transcription from the introduced gene indeed strengthened the sulfur assimilation pathway, and that the generated plants may be practically useful for phytoremediation.