Chemical composition and structural characterization of contrasting colors of soybean seed coats

Seed coats provide protection to seeds and present differential traits between soybean genotypes. The aim of this study was to determine the chemical composition and analyze the internal coat structure of soybean genotypes with contrasting seed coat color, as well as to evaluate the rate of water absorption by seeds. Four genotypes were tested: two genotypes with black seed coat (IAC and TP lines) and two genotypes with yellow seed coat (BMX Potencia RR and CD 202 cultivars). The seeds of the four genotypes were grown during the 2012/0213 crop season, in a greenhouse at the Embrapa Clima Temperado - Estacao Experimental Terras Baixas. After the harvest, the seeds were stored in controlled conditions for five months. After this period, concentration of phenolic compounds, antioxidant potential, anthocyanins, carotenoids, and lignin in seed coats were determined at the Universidade Federal de Pelotas. Internal coat structure was examined on anatomical slides and documented with image capturing software using a microscope at the Escola Superior de Agricultura Luiz de Queiroz, Universidade de Sao Paulo. Finally, water absorption of contrasting seeds was evaluated at 42 hours of imbibition. Experimental design was completely randomized with five replicates. Data were subjected to analysis of variance and the means were compared by Tukey's test, at 5% probability level. Coat structure was characterized by the image analysis. Imbibition data were subjected to regression analysis. The concentration of phenolic compounds, antioxidant potential, anthocyanins, carotenoids, and lignin are higher in black coated genotypes. Their palisade layer and hourglass cells are thicker and the former are more lignified in black seed coats compared to yellow seed coats. The water gain by the seeds is dependent on the conditions in which the seeds were formed and varied between genotypes, independent of coat coloration and lignin concentration.