Differential activity of acid phosphatases from the endosperm and haustorium of date palm (Phoenix dactyliferd) seeds

The acid phosphatase (APase) activity in different parts of ungerminated and germinated seeds of date palm (Phoenix dactylifera L.) was investigated by enzyme assays and on polyacrylamide native isoelectric focusing gels. In the ungerminated seed, APase activity was detected in both the endosperm and the embryo, but the activity was greater in the endosperm. During seedling growth, enzyme activity in the developing haustorium and in the digesting endosperm was 10–15 times greater than that in dry seeds. The APases of the endosperm were different from those of the haustorium: (i) the molecular mass of the enzyme from the endosperm was approximately 52 000 while that of the haustorium was approximately 21 500; (ii) the pH optimum of the APases from the haustorium was 5.0, while it was between 5.0 and 6.5 for those of the digesting endosperm; and (iii) the endosperm contained 6 isoenzymes of pI 3.6–4.3, whereas the haustorium contained 14 isoenzymes with pIs ranging from 5.3 to 6.8. These observations suggest that phosphate metabolism in the endosperm is independent of that in the haustorium and that the APases for endosperm phosphate mobilization are not secreted by the embryo or the haustorium, but instead are stored in the endosperm.