In vitro and in situ localization of concanavalin A and wheat germ agglutinin binding sites on the surface of female cells in Torenia fournieri L.

The interaction between lectins and their specific binding sites is believed to play a critical role in fertilization in animals and some lower plants. However, for higher plants there is no information on lectins or their binding sites related to female gametes and fertilization. The present work was designed as a first attempt to reveal the general pattern of lectin binding site distribution on the surface of female cells, namely egg cells, central cells, and synergids of Torenia fournieri and, especially, to investigate the possible effects of cell isolation procedure on the distribution of lectin binding sites. Therefore, concanavalin A (Con A) and wheat germ agglutinin (WAG) binding sites on the surface of both in vitro and in situ living female cells were localized by using fluorescein isothiocyanate (FITC) conjugated Con A and WGA as probes. We demonstrated that enzymatic treatment and isolation procedures did not notably modify the surface character of the female cells and the distribution of Con A and WGA binding sites. It was also found that Con A binding sites were distributed differently on the surface of the female cells, with the strongest fluorescent signal on central cells and the weakest on egg cells. Calcium could greatly enhance the binding of Con A to the cell surface. A polar distribution pattern of Con A binding sites in embryo sacs was observed. The binding sites were obviously densest at the filiform apparatus of the synergids. The basic pattern of WGA binding site distribution was similar to that of Con A's. However, the fluorescent signal of WGA was much weaker than that of Con A and fluorescent patches were usually found on the cell surface.