ABSTRACT
More than a century after the initial detection of plant lectins by Stillmark, the physiological role of this particular group of plant proteins is still poorly understood. Obviously, the present lack of insight into their possible function(s) cannot be ascribed to disinterest in these carbohydrate-binding proteins because many of them have been studied in detail at the biochemical, physiological and molecular levels (Goldstein and Poretz, 1986). Similarly, as the search for the role of plant lectins has been one of the most important aspects of lectin research during the last decade, the present lack of understanding of their natural function is certainly not due to an insufficient interest in this matter. On the contrary, based on the results of intensive studies, a number of possible physiological roles have been proposed for plant lectins. Clearly, the carbohydrate-binding properties and specificities of the lectins can be regarded as determining factors in the different proposed functions since they enable the phytohaemagglutinins to serve as recognition molecules. Recognition between lectins and receptor molecules can occur at three distinct levels, namely, within the cell, between different cells of the same organism, or between different organisms. As a result, lectins can play a role in the plant itself, in interactions between plants and micro-organisms, or outside the plant.
