Chemical properties of pollen tube growth promoters extracted from transmitting tissue in Pione grape (<i>Vitis vinifera</i> x <i>V. labrusca</i>) pistils

Abstract

The contribution of extracellular matrix (ECM) in pollen tube transmitting tissue (TT) to pollen tube growth ingrape pistils was examined. At bloom the style and ovary septum tissues were excised from blooming Pione (Vitis vinifera × V. labrusca, tetraploid) pistils using a micro capillary. The TT-ECM was extracted by an apoplast extraction method using 1 M NaCl and 50 mM MgCl₂ solutions as extraction solvents. NaCl extracts, except for those with M.W. < 5,000, showed a promotive activity on in vitro pollen germination. By gel filtration of the crude extract two active fractions were recovered; the molecular masses were approximately 40 kDa and < 13 kDa, respectively. The UV spectrum of the higher molecular active fraction, lacking maximum absorption at 280 nm and 260 nm, suggested that the putative pollen tube growth promoter (PGP) might not be nucleic acids or proteins. Carbohydrate component analysis of the 40 kDa PGP using GLC revealed that almost only D-glucose was the constituent. Methylation analysis s howed that the PGP consists of a 1→3 linked glucose unit, a 1→4 linked glucose unit, and a 1→6 linked glucose unit at a molar ratio of 5.6:2.0:1.0. From these results, we postulate that this glucose polymer is one of the PGPs in Pione pistils.