Phytic acid in Petunia hybrida pollen is hydrolysed during germination by a phytase

Phytic acid, which makes up a large proportion of the phosphorus content of Petunia pollen, undergoes only a very slow rate of degradation during the first two hours of germination. After two hours an active phytase (E.C.3.1.3.8) can be detected in pollen extracts and rapid degradation of phytic acid begins in the germinating pollen. Both the rapid degradation of the phytic acid and appearance of phytase activity can be prevented by cycloheximide, but not by cordycepin or actinomycin-D. It is concluded that a pre-existing, long-lived m-RNA in mature, ungerminated pollen is used during germination for the synthesis of phytase, which then catalyses rapid degradation of phytic acid. The product of this reaction is myoinositol, which is needed for pollen tube wall polysaccharide synthesis. The phytase synthesized during pollen germination has maximum activity at pH 5, does not require metal ions and is inhibited by fluoride and inorganic phosphate. The degradation of phytic acid and pollen tube elongation are retarded by inclusion in the medium of concentrations of phosphate inhibitory to phytase.