Analysis of lignin in seeds and peroxidase and laccase enzymes activity in the arils of some soft- and hard-seed pomegranate genotypes at different fruit developmental stages

In order to study seed hardening process in pomegranate، some of the relevant biochemical parameters were evaluated in fleshy part of arils or seeds in various soft and hard seeded pomegranate genotypes from the initial fruit set upto ripening stages. Lignin was determined from the seeds and enzyme assays were performed on the flesh of arils. Analysis of variance revealed significant differences among different genotypes and stages. At the first stage that the seeds of all genotypes were soft، the peroxidase activity was relatively high and decreased in the second (start of the seed hardening in hard seed genotypes) and third stages. Thereafter، at the final stages، it increased in the hard seed genotypes (four times of that in soft seed genotypes)، whereas remained low in the soft seed ones. Laccase activity during the growing season had a non predictable trend and did not show much differences in the soft and hard seed genotypes، although in most of the genotypes، its activity decreased at the last stage. In the soft seed genotypes، total protein was in the highest value at the early stage، and decreased at the second stage، then in the next stages، after a little increase، reached to a constant amount. In the hard seed genotypes، the total protein decreased until the third stage، afterward increased to the ripening. The protein content of soft and hard seed genotypes in the last stage of sampling reached to the same value. Lignin content of pomegranate seeds increased gradually during different stages، and the soft seed genotypes had less lignin in their seed compared to the hard seed ones. According to the results، considerable differences that were observed in the peroxidase activity at the last sampling stage، and higher activity that observed in peroxidase than laccase (at least 10،000 times)، may indicate a main role for this enzyme to make differences in the seed hardness of pomegranate.