METABOLISM OF PHYTIC ACID IN POLLEN OF LILIUM LONGIFLORUM THUNB. AND MATHEMATICAL MODELING OF WALL POLYSACCHARIDE FORMATION DURING POLLEN TUBE GROWTH (PHYTASE, SIMULATION).

摘要

Phytic acid metabolism in seeds has been studied extensively, however, literature about phytic acid metabolism in pollen is limited. The accumulation of phytic acid during development of lily pollen and its degradation during germination and tube growth were studied. Phytase which is responsible for phytic acid breakdown was isolated from ungerminated and germinated lily pollen and was characterized and partially purified.;Two phytases were isolated from germinated lily pollen. They differ in size and affinity for a diethyl aminoethyl column as well as in optimal pH. The time-course study revealed that the activity of phytase increased as germination proceeded. The phytase (72 kD) with a pH optimum at 5.0 was present in mature ungerminated pollen, but the pH 6.5 phytase (36 kD) was newly synthesized from a pre-existing mRNA during germination. The evidence suggested that the low pH phytase may be effective on phytic acid breakdown only during early germination, and pH 6.5 phytase was the enzyme required for further breakdown of phytic acid.;Mathematical models based on the kinetic constants of relevant lily pollen enzymes from glucose to wall polysaccharides were developed to understand how flux of carbon through the sugar nucleotide and myo-inositol oxidation pathways is regulated and the relative importance of the two pathways. The changes of sugars and myo-inositol during germination were determined in order to have data for the model. The model was constructed with Michaelis-Menten equations for the various enzymes, but in some cases K(,eq) was used instead. Several enzymes are inhibited by product or an allosteric inhibitor, so terms are added to take these inhibitory effects into account. Computer simulation of the pathways was carried out, and simulated rates of production for various wall sugars were compared to values published for growing pollen tubes.;A substantial amount of phytic acid has accumulated in lily pollen by 5 days before anthesis, and little change occurs during subsequent maturation. Considerable degradation of phytic acid has occurred by 15 min of incubation in the glucose medium, and very little is left by 3 h. The breakdown of phytic acid proceeds at an approximately constant rate (0.037 ug phytic acid /mg pollen/min) during this time.