Matric Potential of Several Plant Tissues and Biocolloids

Abstract

Summnary. The pressure membrane apparatus was used to study the matric potential (imbibition pressure or moisture tension) of plant tissues and of several organic colloidal preparations.The moisture release curves of aqueous 2 % agar, 12 % gelatin, and filter paper were smooth parabolic curves between matric potentials of -0.1 and -15 bars. When logarithms of the matric potentials were plotted against logarithms of the moisture content, the data yielded straight lines for agar and filter paper.Slices of fresh tissue lost little water after 2 days in the apparatus at maximum pressure of 15 bars. Osmotic forces in conjunction with cell membranes are able to retain moisture against pressure of this magnitude. After the cells were disrupted by freezing and thawing, up to 90 % of the original moisture was removed by a 15 bar pressure, with lesser amounts removed at lower pressures. The results gave a parabolic relationship, and straight lines could be fitted to log log plots of data from potato tuber and young asparagus stem slices. Sections from the tips of asparagus stems held less moisture at all matric potentials than more basal sections.The method permits the study of the matric potential of tissues independently of the osmotic potential. As meastured, however, the matric potential is a composite of matric potentials of colloidal substances in the protoplasm and cell walls after disruption of cells by freezing and mixing of the contents. The value is therefore only an approximation of the matric potentials occurring in the living tissues.The condition of water in plant cells can be described in terms of the relationship = = 7r + qIp + mn in which if is the water potential, qf, the osmotic potential due to solutes, tp the turgor pressure or pressure potential, and qlm the matric potential due to adsorptive forces of colloids. The relative contributions of the osmotic and matric potentials to the water potential have not been extensively studied. Instead, in most discussions on the water relations of mature, vacuolate cells, it is tacitly or explicitly assumed that the adsorptive forces are quantitatively of minor importance relative to osmotic forces, and -often they are not mentioned.The rationale for neglecting the contribution of surface forces in discussions of the diffusion pressure deficit (DPD) is that the proportion of cytoplasm is small in the vactuolated cells which are generally chosen for discussion and that the contribution of adsorptive forces would therefore be minor. Also, it is c-ommonly observed that when

Matric Potentials of Leaves

“…However, additional water is undouibtedly expressed from cell walls when pressures are applied to the tisstue, especially at low pressures. Filter paper has been shown to lose water most rapidly at matric potentials above -4 bars (17). Below that potential, water loss was negligible.…”

“…Wiebe (17) has shown that matric forces exist in fleshy stems (asparagus) and storage organs (potatoes and mangels) btut he concludes that they are small in these organs over the physiological range of water contents. Matric potentials have been postulated for plant leaves (6,16,17) but they have not been measured.…”

“…Matric potentials have been postulated for plant leaves (6,16,17) but they have not been measured. In this report, I show that plant leaves have significant matric potentials and present evidence that the matric potentials which are observed are associate(d mainly with the cell walls.…”

Method for Determining Solutes in the Cell Walls of Leaves

“…This is very much the case for the cell walls of leaves and other aerial organs whose total water potential is directly measured whenever the water potential of the tissue is studied but whose water potential components, matric and solute, are completely unknown. Data on the relationship of matric potential to water content of killed plant tissues (3,11) are not helpful in determining the matric potential in cell walls. Even if the water content determination were specific for the cell wall, the water content of the cell wall cannot be inferred from water content of intact tissues, so the matric potential of the cell wall remains unknown even when total water potential and tissue water content are determined.…”

Ecophysiology of the holoparasitic angiosperm Cistanche phelypaea (Orobancaceae) in a coastal salt marsh

“…Studies have indicated that the stem parasite Cuscuta reflexa exerted a very strong sink and competed efficiently with the major host sinks by attracting 81% of the current photosynthate and 223% of nitrogen, more than was currently fixed (Press, 1995). Moreover, the presence of starch may imply the existence of a matric component (Wiebe, 1966) that produces surface forces that account for a minor portion of cell's water potential. Accordingly, the water retaining forces of the parasite (especially the tuberous part with the highest starch content and nearest the host root) are expected to be higher due to the Ψ w alone.…”