Abstract: 【Objective】 The effects and mechanisms of UV-B on pollen tube growth and cell wall construction were investigated in the gymnosperm, Picea wilsonii.【Method】To determine the effect and suitable radiation density of UV-B on pollen tube growth of gymnosperms Picea wilsonii, the pollen tube length and tube tip width were measured when pollen grains were incubated for 24 h under visible light with different densities of UV-B radiation. To determine the effect of UV-B on the pollen tube cell wall constructions, pollen grains were incubated for 24 h under visible light alone or in conjunction with suitable UV-B radiation density, and the distribution of cellulose and callose stained with calcofluor and aniline blue, respectively in the pollen tube cell walls were observed under fluorescence microscopy. The distribution of acidic and esterified pectins in the pollen tube cell walls were observed under laser scanning confocal microscopy using the immunolabeled monoclonal antibodies LM19 and LM20, respectively. 【Result】 When pollen grains were incubated under visible light with 0, 0.2, 0.4, 0.6 and 0.8 W·m^-2 UV-B radiation for 24 h, the pollen tubes were gradually shortened and many of them exhibited swollen tips with increasing density of UV-B radiation. This indicated that UV-B inhibits pollen tube growth in a density-dependent manner. When UV-B radiation density was increased to 0.4 W·m^-2, the pollen tube growth was significantly inhibited, suggesting that 0.4 W·m^-2 is a sufficient UV-B radiation density to inhibit pollen tube growth of Picea wilsonii. Under visible light alone, cellulose was distributed uniformly in the wall of pollen tubes, callose was uniformly distributed along the tube shank with a very faint distribution in the apical region of pollen tubes. Acidic pectins were deposited along the tube except in the apical region, while esterified pectins were present only at the tube tips. Under conditions of visible light with 0.4 W·m^-2 UV-B radiation, the distributions of cellulose and callose in the apical region of pollen tubes were significantly higher than that in the tube shank. Acidic pectins were mainly deposited in the apical and subapical regions of pollen tubes, while esterified pectins were deposited throughout the wall of pollen tubes.【Conclusion】UV-B radiation inhibits the polarized growth of Picea wilsonii pollen tubes via affecting the normal orientation distribution of construction components of the pollen tube cell wall, such as cellulose, callose, acidic and esterified pectins.

Key words: UV-B radiation, Picea wilsonii, pollen tubes, cell wall construction, polarized growth