title: [Mobilisation of reserve mannan in germinating date seeds].
abstract: Morphological and biochemical studies of the decomposition of endosperm tissue in germinating date seeds have shown that the mobilisation of reserve substances is effected with the help of exoenzymes. The depolymerisation of the mannan chain takes place in a "dissolution zone" surrounding the haustorium. This dissolution zone can be further divided into two sub-zones; a primary zone (consisting of several cell layers) where the secondary wall becomes swollen but does not lose its form, and a secondary zone (much smaller) where the mannan is broken down to mannose residues. The cellulose of the primary wall resists decomposition and remains as threadlike elements in the secondary zone.From the results of qualitative and quantitative sugar determinations it is evident that mannose is the endproduct of mannan decomposition. The mannose is then absorbed by the haustorium.From incubations in vitro of solutions of mannan A with haustoria a number of oligosaccharides were isolated. The substances found included fragments of pure mannan chains containing 1-5 mannose residues. In much smaller amounts oligosaccharides containing glucose and mannose residues were found. It is of interest to note that myoinositol was also detected.The failure to detect phosphorylase activity and the absence of phosphorylated intermediary products in the dissolution zone suggest that a hydrolytic process must be involved in the decomposition of the mannans.After absorption by the seedling, mannose is converted into sucrose, but the mechanism of this synthesis was not clearly determined. No sugar nucleotides were detected in the dissolution zone. In in vitro experiments with enzymes extracted from the haustorium (to observe possible sugar nucleotide formation) only UTP, and not GTP, was found to react with mannose.A possible reaction scheme for the conversion of mannan to sucrose is proposed, and form in which sugar is transported from the endosperm to the seedling is discussed.
authors: Botanisches Institut der Universität Fribourg, Schweiz.
authors: L
authors: L
authors: Keusch