Water Relations of Plant Cells

Cytoplasmic Electric Fields and Electroosmosis: Possible Solution for the Paradoxes of the Intracellular Transport of Biomolecules

“…Therefore, one might speculate on the possible wider implications of electroosmotic flow in the biological processes, including cytoplasmic streaming in plant and embryonic cells and perivascular transport of proteins in brain. The aim of this paper was to draw the attention of the biologists and biophysicists to this important physical phenomenon well known in separation science and microfluidics, however, largely ignored in biology, the main exception being the plant physiology [29]–[35], where electroosmosis was recognized as a mechanism to pump water upward through the phloem.…”

“…These conditions are simple and are likely to be satisfied in many biological systems. Surprisingly, intracellular electroosmosis has been ignored so far with the exception of one scientific field–plant physiology, where the series of studies [29]–[35] published mostly in 1950–1970s discussed the possible role of electroosmosis in the transport of water and nutrients in the plant tissues. In particular, electroosmosis was hypothesized to be the mechanism for the transport of sugars along the cytoplasm of the sieve tube cells of the phloem of the higher plants, while the electric potential was assumed to be generated by the active uptake of the K + ions by the companion cells of the phloem [30].…”

Water Relations of Plant Cells and Tissues

“…Most investigators seem to depend on differential permeability to various ions to explain such a mechanism, or they postulate continuous production of some such substance as bicarbonate ion which accumulates at the inner membrane surface. Bennet-Clark and Bexon (73) for example, concluded from experiments on onion epidermis that electro osmosis resulted from more rapid diffusion of K+ than Cl-through the nega tively charged cell membranes. No energy was directly expended in this instance, but if the protoplasm expends energy in maintaining a potential difference, as it does in at least some cells, then electroosmosis must be re garded as a form of active water absorption.…”

“…Lund (72) believed that the potential differences which he -found in roots of woody plants might be large enough to cause inward and upward movement of water and the development of root pressure. Bennet-Clark & Bexon (44,73) have proposed an electroosmotic mechanism to explain the movement of water across the cytoplasm into the vacuole. Brauner & Hasman (59,74) and Studener (75) support the view that there is an electroosmotic compo nent in the uptake of water by bulk storage tissue.…”

Osmotic Pressure of Vacuolar Sap by the Plasmometric Method

“…If our suggestions concerning the properties of the cytoplasm and the vacuole are justified it is not surprising that plasmometric estimates of the osmotic pressure of the vacuolar sap exceed the true value and that Bennet-Clark and Bexon (1946) should observe that the volume of protoplast plus vacuole should be greater in cane sugar solution than in an isosmotic solution of an electrolyte.…”