The effects of boron on polyphenol oxidase activities in embryo and endosperm tissues of wheat seeds during germination

The effects of boron (B) on the germination rate and polyphenol oxidase activities in embryo and endosperm tissues of two wheat cultivars ((Triticum aestivum L. cv. Kıraç-66 and cv. Sultan-95) were investigated. The germination percentage of both seeds was not effected by boron concentrations up to 50 mM, and decreased by 100 and 150 mM. Distilled water and lower B concentrations (0.1 and 50 mM) increased polyphenol oxidase activities at the beginning of germination up to 6 hours in Kıraç-66 and 9 hours in Sultan-95 whereas its excess levels (100 and 150 mM) decreased polyhenol oxidase activities in embryos and endosperm during germination. In the both cultivars, polyphenol oxidase activities with o-diphenolic substrates (catechol, dopa and caffeic acid) were found to be higher than with a monophenolic substrate (tyrosine) in both embryos and endosperms.In Sultan-95 cultivar, polyphenol oxidase activities with o-diphenolic substrates were higher in embryo than endosperm, and dopa oxidizing polyphenol oxidase was found to show more activity than other substrates. Polyphenol oxidase activity with monophenolic substrate was higher in endosperm than embryo. On the other hand, in Kıraç-66 cultivar dopa and caffeic acid oxidizing polyphenol oxidase activities were high both in the embryo and endosperm tissues. In conclusion, high concentrations of boron decreases germination rate and polyphenol oxidase activities in seed tissues, and Kıraç-66 cultivar was more tolerant to high boron than Sultan-95 cultivar.Key Words: Boron, embryo, endosperm, germination, polyphenol oxidase, wheat