J Integr Plant Biol. ›› 1955, Vol. 4 ›› Issue (3): -.

• Research Articles •    

Protoplasmic Continuity in Plants

C. H. Lou   

Abstract: How the plant acts as an entity to adapt itself to the ever changing surroundings is a problem of fundamental importance[1,7]. The problem has been put forward to the botanists by the theory of Michurin and Parlor, both of whom have proved with their own experiments that living beings are in unseparable unification with their environment. As we know, along the evolutionary steps that lead lower and simpler forms of life to higher and more complicated ones, the more the differentiation of functions among the constituent parts, the more the needs for closer coordination among them. Hence, the plant must integrate the various processes in metabolism conducted in its various parts into a united whole in order to "equilibrate" with external changes. To put it more concretely, in a plant body which is consisted of innumerable cells, each cell being entirely enclosed in a rigid wall, intimate coordination among its physiological functionings, proper responses to local and transmitted stimuli, timely translocation of manufactured food and efficient distribution of absorbed minerals must be effectively maintained. The attempt to solve these problems of plant integrity is to try to synthesize the individual physiological phenomena on a common ground, to realize the interlocking connections involved, and, finally, to serve as a more effective guide in controlling nutrition, growth and development in plants. It has been generally accepted among the botanists that the living cells constituting a plant are interconnected by protoplasmic threads (Plasmodesmata) so that the plant is a definitely correlated entity of interconnecting protoplasts (Symplast)[42]. So far evidences of protoplasmic continuity in plants mainly come from anatomical observations on dissected tissues. Based upon these facts, plasmodesmata have bean suggested as channels of translocation of organic solutes. Consequently, the symplasmic nature of plant has been incorporated in Münch's theory of mass/low of organic solutes. Conduction of stimuli has been regarded as a second function (Haberlandt)[13]. Direct evidences, however, for any such role of plasmodesmata are wanting. On other occasions, the presence of plasmodesmata has been ignored or considered irrelevant. Lund et al[50], in their investigations on bioelectric fields in plants, have never taken into consideration how such protoplasmic continuity would affect potential and current distribution in plants. Lundegardh[40], in his investigation on the translocation of salts through roots, does not believe that it is necessary to visualize a symplast to account for this process. The cited examples are sufficient to indicate that we are altogether uncertain of the role of plasmodesmata in the physiological functionings of plants and due attention has not been paid to them.

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