Matric Potentials of Leaves

Abstract

SummDlleary. A pressure chamber was used to measture matric potentials of frozen and thawed leaves. Significant matric potentials were demonstrated in sunflower (Helianthus annuus L.), yew (Taxus cuspidata Sieb. and Zucc.), and rhododendron (Rhododendron roseum Rehd.). Matric potentials were particuilarly negative in rhododendron and were correlated with the amount of cell wall present and with the voluime of water outside the leaf protoplasts at comparable matric potentials. It was concluded that matric forces in leaves are associated mainly with cell walls, at least within the physiological range of water contents. Calculations indicated that the water potential of the solution in the cell wall could be estimated for living tissue from the suim of matric and osmotic potentials acting on water outside the protoplasts.The availability of water to soil-grown plants is determined in largest part by the interaction of water with the surfaces of soil particles and by the effects of soil solutes. It has been convenient to group the surface forces, tusually adsorptive and capillary forces, in a single term, matric potential (2,9,15,16 PLANT PHYSIOLOGY potential has uistually been sttdiedl in systems with -arying water contents (10, 1t) and this is the approach adopted here. Materials and MethodsThree species having leaves and stems of widely different anatomy were chosen for sttudy: suinflower (Heliant has annuas L.), yew (Taxuts cutspidata Sieb. and Zucc.), and rhododenidroin (Rhododendron roseumn Rehd.). Two year old yew and rhododendron were grown in soil in the greenhouise. Sulnflower was groxvn from seed in soil in a controlled environment room (temp, 30-31 (lay and 27-28' night; relative humidity, 45-55 %; light, 2500 ft-c).Matric potentials were measured with a pressture chamber (12,13) in leafy shoots 20 to 30 cm long (rhododendroni and yew) and leaves (suinflower) that hadl been frozen at -20°and slowly thawed. The chamber was slightly modified by bubbling the incoming nitrogen gas through water in the bottom of the chamber to prevent drying of the tisstle. A baffle prevented the water from splashing onl the tissue.Matric potentials were (letermine(d as a ftunction of the water content of the plaint tissue by placiing a frozen and thawed plaint sample in the pressuire chamber with the cuit stem protrutding through the top of the chamber. Several aliquiots of cell sap were expressed by raising the pressuire aroulndl the plant sample. After each aliquiot was removed, the balancing pressure was (letermined and( represeinted the matric potential at that water content. Following the measturement of matric potentials, the total water in the sample was (letermined by Ir-ing at 100°and adding the water loss (dtiring (Irving to the volume of cell sap in aliqulots collecte(d while the sample had been subjected to presstire.The a-erage cell wall volume of the leaf mesophyll cells was determined after stainiing fresh leaf cross sections with Schiff reagenit by the PAS method (8). The average volume of the protoplast a...

Chloroplast Response to Low Leaf Water Potentials

“…It has been suggested that the so-called negative turgor could arise because the stiffness of the cell wall may resist shrinkage as water is lost from the cell (30). However, in sunflower leaves, the resistance to shrinkage is only a fraction of a bar at the T,, in Table 11 (6). Consequently, the apparent negative turgor could have been due to dilution of the cell sap as a result of mixing of the protoplast and cell wall solutions after membranes had been disrupted by freezing and thawing the tissue during the determinations of T. .…”

“…Since most of the loss in photochemical activity occurred at water potentials below -10 bars, it was concluded that turgor had little effect on the photochemical activity of the leaves. tentials and matric potentials were negligible (6) in the protoplasm of the leaves used in this work. Thus, w,, was determined primarily by 1,, and T..…”

“…(8,20), and this procedure was followed in the present work. Leaf Tp was then calculated from the difference between leaf I,,, and P, according to equation 1, assuming TI,, and Pg to be negligible in the protoplasts (6).…”

Ecophysiological characteristics of Avicennia germinans and Laguncularia racemosa coexisting in a scrub mangrove forest at the Indian River Lagoon, Florida

“…This balance pressure is analogous to the matric potential ( m; Passioura 1980). The m is similar to total provided that xylem π is near zero (Boyer 1967(Boyer , 1969Kramer and Boyer 1995). In mangrove species, xylem π is well below zero representing an important fraction of their (Scholander et al 1966).…”

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.…”