Tissue-specific Soluble Sugars in Seeds as Indicators of Storage Category

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Abstract
The accumulation of specific soluble carbohydrates has been implicated in the acquisition of desiccation tolerance and improved longevity in orthodox seeds, leading to the hypothesis that carbohydrate composition might be used as a diagnostic marker for seed storage category. We have studied the sugar composition of 46 tissues from seeds of 18 species, covering 13 genera and ten families, and representing three seed storage categories: orthodox, intermediate and recalcitrant. Soluble carbohydrate extracts from each tissue were analysed using High pH Anion Exchange Chromatography. Total sugar content and sucrose level of the embryo were highly variable across all species and no simple association with seed storage physiology was evident. Monosaccharide levels were found to be low in most seeds studied, including those of the recalcitrant category. Sucrosyl-oligosaccharides, raffinose and stachyose, were observed to be lower in recalcitrant seeds compared to orthodox seeds. In general, orthodox and recalcitrant seeds had tissues with sucrosyl-oligosaccharide:sucrose mass ratios of > 0·143 (i.e. 1:7) and < 0·083 (1:12) respectively. Moreover, large variations in the content of these sugars were noted between different tissues within the recalcitrant and intermediate seeds. The results from the present study in combination with data in the literature show that the ratio of sucrosyl-oligosaccharide isucrose in seed tissues is generally a good indicator of seed storage category.

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