Osmotic Quantities in Growing Cotton Bolls

Abstract

WITH TWO FIGURES)Regional variety tests have shown that the tensile strength of cotton fibers of any giveni variety is influenced by environmental conditions. In general, the fiber seems to have greater strenigth wheni plant growth is checked by deficient water and less strengicth when water is not a limitinog factor. This observation has led to the assumption that the strength of cotton fibers might be influenced appreciably by the turgor of the developing fiber cells. If this assumption were correct, a knowledge of cell turgor, at critical stages in the growth of the fiber, should serve as ani inidex of the tensile strength of the fiber. Since tensile strength is a property-of the greatest importance, efforts were made to determine the diurnial and seasonal variations in turgor in the developing seeds of upland eottoin grown in Raleigh, N. C.Cell turgor cannot be imeasured directly btut it can be estiimiated indirectly in two ways: (a) byr measuring volume changtes in the cells, and (b) by determining the differenice between the osmotic pressures and the diffusioni pressure deficits of the growing cells (11). Both methods have been employed by the writers. The data obtained by the use of the first method have beenl reported in a previous paper (1). This paper is a report of the results obtained in the application of the seconid method.The osmiiotic quantities of plant cells and their relation to the intercellular movements of water have beein diseussed by URSPRUNG (15) and by MEYER (11). The terminology used by MIEYER is adopted in this paper.The movement of water between plant cells, and between cells and their environment has commonlv been regarded as an osm1otic phenomnenioni. The osmotic quantity designated as the diffuision pressure deficit is generally regarded by physiologists as having a mutch greater significance in determining the direction and rate of water movements into and out of plant cells than the osmotic pressure of the cells (12). This is due to the fact that the direction and rate of water miiovement between cells is believed to be controlled bv the relative diffusion pressure of the water in the different cells. Movement of water will occur from regionis of higher to regions of lower difftusion pressure. The diffusionl pressure of water is influenced both by the osmiiotic pressure and by the turg-or of the cells. The presence of solutes decreases the diffusion pressure of water. The amount of this reduction of diffusion pressure is equivalent to

Water Relations of Plant Cells and Tissues

“…Kerr & Anderson (49) observed that while the osmotic pressure of sap expressed from young cotton seeds exceeded their DPD as measured gravi metrically, in seeds 24 days old the DPD exceeded the osmotic pressure, the difference increasing with age of the seeds. Neither the DPD nor the amount of water absorbed was decreased by potassium cyanide or other treatments which inhibit respiration, and it was concluded that the vacuolar sap prob ably was contaminated with sap from the cytoplasm, released by freezing prior to expression of sap.…”

Water in the physiology of plants, by A. S. Crafts, H. B. Currier and C. R. Stocking.

“…Small samples from a single tissue type are more significant than large mixed samples. With any sample, dilution of the vacuolar sap by water liberated by alteration in physical organization of colloidal matter may constitute a real limitation (Newton, Brown, and Martin, 1926; Meyer, 1928; Jaccard and Frey- Wyssling, 1934 ; Roberts and Styles, 1939 ; Kerr and Anderson, 1944 ; Currier, 1944a). Walter and Weismann (1935) consider this not to be a source of error.…”

“…In their opinion, the simplified method, used for DPD, yielded values which were too high, especially when leaves in a wilted or nearly wilted condition were measured. Kerr and Anderson (1944) That a considerable proportion of the DPD may at times be due to the development of high tensions has been emphasized by some. Such negative wall pressures, in intact leaves of trees, especially during periods of abnormally high water loss, may exceed the influence of osmotic effects on the DPD (seeCuv, 1936).…”

“…Data on this point would be helpful. Kerr and Anderson (1944) studied the osmotic quantities of cotton seeds in various stages of growth. In seeds less than 24 days old OP values exceeded the DPD, a relationship to be expected.…”

“…Imbibitional forces thus were believed to account for the difference between the two measurements, which is "more apparent than real." Anderson, 1944) : -…”