Plant polysome binding to the actin cytoskeleton as a target for physiological regulation

Abstract

One of the principal functions of the actin cytoskeleton is to serve as a support for diverse physiological and biochemical processes, protein synthesis in particular. About 25 years ago, in experiments with cultured animal cells, it was discovered that most mRNAs, ribosomes, and protein synthesis factors were attached to the actin microfilaments (Lenk et al., 1977). Later, a similar phenomenon was demonstrated for plant tissues (Davis et al., 1991; Zak et al., 1995). The physiological basis for such an attachment is evident in some cases but obscure in others. Attachment of polysomes to the microfilaments might provide for the correct spatial arrangement of the translational machinery and protein synthesis activation. If the binding of polysomes to the cytoskeleton is considered an additional level of protein synthesis regulation, its physiological control is expected but is not shown, at least for plant cells. To evaluate the proportion of the cytoskeleton-bound polysomes (CBP) in the total polysome population, we used the differential sensitivity of membranes and cytoskeleton to nonionic detergents that destroy membranes but leave microfilaments intact. A difference in the polysome peak areas in sucrose density gradients of plant tissue homogenates treated and nontreated with Triton X-100 was a rough measure for the amount of CBP (stretched areas in Fig. 2). * Corresponding author. Tel.: +7-95-432-0233; fax: +7-95-977-8018.