ASCORBATE METABOLISM IN MATURE POLLEN GRAINS OF DASYPYRUM-VILLOSUM (L) BORB DURING IMBITION

A mature pollen grain of Dasypyrum villosum, roundish in shape with a single germinal pore, is tricellular and rich in starch granules. Pollen grains are endowed with the ascorbate biosynthetic pathway and actively synthesize ascorbic acid. In D. villosum pollen the two main oxido-reduction enzymes of the ascorbate system, AFR reductase and AA peroxidase, are present with a high activity; DHA reductase activity is very low and there is no AA oxidase. Ascorbate peroxidase activity is shown to be 10 times higher than that of catalase, indicating that ascorbate peroxidase, rather than catalase, is the key enzyme to remove H2O2 produced in the cell metabolism. AA peroxidase and AFR reductase are released in the germinating medium; their possible role is discussed.