Evaluation of an Anthocyanin, Cyanidin 3,5-di-O-glucoside, as an Allelochemical in Red Callus of a Mangrove Sonneratia ovata, Using Protoplast Co-Culture Bioassay Method with Digital Image Analysis

protoplasts to examine the allelopathic activities. Protoplasts were isolated with Cellulase R10 and Driselase 20 in 0.6 M mannitol solution and purified by density gradient centrifugation on 0.6 M sucrose. Protoplasts were co-cultured in 50 μL of liquid Murashige and Skoog’s (MS) basal medium containing 1 μM 2,4-dichlorophenoxyacetic acid and 0.1 μM benzyladenine and 0.6 M mannitol solution in a 96-well culture plate. Protoplast density ranged from 5 × 103/mL to 105/mL. Cell division of lettuce protoplasts was strongly inhibited by addition of S. ovata protoplasts, and non-spherical cell enlargement was slightly inhibited. By contrast, digital image analysis of scanned 96-well culture platesrevealed no inhibition in accumulation of yellow color in lettuce protoplasts. An anthocyanin, cyanidin 3,5-di-O-glucoside (cyanin), was identified and its content in the red callus was ca. 1 mM of fresh weight. The effects of cyanin on the growth of lettuce protoplasts at three stages were similar to those of red S. ovata protoplasts. From these results, cyanin was most likely the allelochemical contained in red callus of S. ovata. The allelopathic activity of cyanin was compared with that of other putative allelochemicals in several plant materials, using the protoplast co-culture method with digital image analysis.