Gene expression profiles of cold-stored and fresh pollen to investigate pollen germination and growth.

In lily (Lilium longiflorum cv. Avita) pollen cold-stored (-20 degrees C) for 2 months, typical in vitro germination/growth was delayed by about 1 h compared with fresh pollen. We hypothesized that some proteins and mRNAs stored in mature pollen were degraded during storage periods and that re-synthesis of them was essential to resume normal germination and growth. Cold-stored and fresh pollen grains were used to investigate the regulatory mechanism of pollen germination and tube growth in terms of both total protein profile and gene expression. Total protein profiles of cold-stored pollen differed qualitatively and quantitatively from fresh pollen. Actinomycin D significantly inhibited both germination and tube growth of cold-stored pollen and later tube growth of fresh pollen but had no effect on fresh pollen germination and early tube growth. Suppression subtractive hybridization screening revealed 99 cDNAs enriched in fresh mature pollen, and 22 were selected for further characterization. Most of these 22 cDNAs gradually disappeared during cold storage, but full recovery was achieved by incubating the cold-stored pollen in culture medium for 2 h. Because of different sensitivities to cold storage and actinomycin D, the transcripts were divided into three groups according to their possible roles in pollen germination and tube growth. Several cDNAs encoding novel proteins showed pollen-specific expression patterns and may participate in drought tolerance (an Na+/H+ antiporter), endomembrane trafficking (DnaJ), division of the generative cell (Sgt1), pollen wall precursor uptake from stylar exudate (an Na+/myoinositol symporter) and chemotropism of the pollen tube (peptide transporter) during pollination.