Boron Deficiency Causes Changes in the Distribution of Major Polysaccharides of Pollen Tube Wall

In an attempt to understand the functions of boron in the regulation of Pollen tube growth, thestructure and localizat ions of two major polysaccharide components, pectins and callose, in cell walls were studied in pollen tubes cultured in standard medium and boron-deficient medium, respectively.Immunochemical localization of acid pectin and methyl-esterified pectin in the walls of pollen tubes of tobacco (Nicotiana tabacum L. cv. Petit Havana ) and lily (Lilium longiflorum Thunb. ) was investigated by using monoclonal antibody JIM7 and JIM5 and observed by means of confocal laser scanning microscopy (CLSM).Most of the boron-deficient pollen tubes were remarkably labelled by JIM5 in the wall of tip region,demonstrating an abnormal accumulation of acid pectin in the pollen tube tip, which is the only growth region of the cell. The localization of (1-3)-β-D-glucan (callose) in the walls of pollen tubes was revealed by ultraviolet excitation of aniline blue staining. The accumulation of callose was also found in the wall of the tipregion of the pollen tubes cultured in the boron-deficient medium. In addition, the changes in the structures of pectins and phenols were investigated by fourier transform infared (FTIR) microspectroscopy. It was further confirmed that boron deficiency caused the increment of acid pectin in the pollen tube walls. The increase in the content of phenolics and the decrease in that of phenolic esters were also revealed in boron-deficient pollen tubes. These results imply that boron may function as a regulatory factor of pollen tube growth by affecting the activity of the corresponding enzymes that induce the changes of polysaccharide network and thus the extensibility of the cell wall. The accumulation of free phenolic compounds influences the integrity of plasma membrane, which might also contribute to the regulation of pollen tube growth.