Pigment composition and location in honey locust (Gleditsia triacanthos) seeds before and after desiccation

Abstract

Gleditsia triacanthos L. pods were harvested at San Lorenzo del Escorial, Madrid, Spain, before and after seed desiccation. Maturing green pods, harvested from trees, contained soft light-green seeds, whereas fully mature brown pods, collected on the ground, contained hard dark-green seeds. Based on visual inspection of seeds, it was determined that the green color is located in the cotyledons and embryo of soft seeds but mainly in the seed coat of hard seeds. High performance liquid chromatographic analysis indicated that both hard and soft seeds contained the same set of photosynthetic pigments as fully developed leaves, but in different proportions. The hard and soft seeds mainly differed in their chlorophyll a to chlorophyll b ratio and in the composition of the xanthophyll cycle pool of pigments. Fluorescence at -196°C revealed that the molecular organization of the pigment molecules in the seed coat of hard seeds differed from that in intact cotyledons of soft seeds and intact green leaves. The -196°C fluorescence spectra also revealed the presence of a small heterogenous pool of non-photoactive protochlorophyll(ide)s, similar to those found in dark-grown tissues of gymnosperms and angiosperms.