Solutes in the Free Space of Growing Stem Tissues

Abstract

The concentration of osmotically acthve solutes in the cell wall free space of young stem tissues was studied using a variety of extraction methods. When the intercellular air spaces of etiolated pea (Piswm sauivwm L.) internodes were perfused with distilled H20, the resulting solion contained a solute concentration of about 70 miliosmoles per kiogram. A second procedure involving vacuum infiltration of segments followed by centrifugation to coDlect the free space solution gave similar results. Apical stem segments yielded free space extracts about twice as concentrated as those from basal portions of the stem. After correcting for dilution of the free space solution by the infiltrated water, the osmotic pressure of the undiluted free space in pea stem tissue was estimated to be 2.9 bars for apical segments, Wayne) seedlings were grown in wet vermiculite in complete darkness at 27 ± 1 C and low RH (20-500o, not controlled). Plants were handled under dim green light obtained from a 40-w cool-white fluorescent lamp filtered through one amber and two green acetate filters (Roscolene No. 813 and No. 874; Roscoe, Port Chester, NY). Seedlings 6 to 8 cm tall were selected for experimentation; all subsequent operations were performed in the light. In some cases, pea seedlings were carefully removed from the vermiculite, the cotyledons excised with a new razor blade (under dim green light), and the seedlings replanted in vermiculite to grow for 2 d more in complete darkness.Osmotic Pressure of FS (e). The solution which makes up the cell wall FS was collected by three different methods, and 8-,ul samples were measured in a vapor pressure osmometer (Wescor model 5100; Wescor, Logan, UT). The osmometer was calibrated in the 0 to 100 mOs.kg-' range before and after all measurements.Osmolality was converted to osmotic pressure (at 20°C) by multiplying the value in Os.kg-' by 24.37 bar.Os`kg.The FS solution was collected in the first method by forced perfusion of the intercellular air channels with water. In this method, the basal ends of five excised segments were sealed with quick-setting epoxy (Qwik-Stik; GC Electronics, Rockford, IL) into a pressure vessel completely filled with water (Fig. 1). The vessel was pressurized using a gas cylinder, and the fluid which exuded from the ends of the segments was collected with a capillary tube. Excision was made under water (so the contents of the cut cells would be immediately released to the water), and the segments were incubated on water for 30 to 40 min on a rotary shaker before being placed in the apparatus. In a variation of this method, intact pea seedlings were sealed with epoxy into the lid of the pressure vessel, such that 4 to 5 cm of the shoot extended outside ofthe vessel (Fig. 1)

Osmotic Properties of Pea Internodes in Relation to Growth and Auxin Action

“…Second, when the air spaces of stems were perfused with water continuously for 20 min, P increased by 1.2 bars. Such perfusion would be expected to flush out the solutes from the free space and thereby increase P. The fact that did not quite reach 0 bar is in agreement with independent observations that perfused pea stem tissues continue to efflux solutes to the free space (7).…”

“…The chemical identity of the solutes, and explanation for their high concentration in the free space, has yet to be established (7). One possible explanation is that the cell membrane does not behave as an ideal semipermeable membrane, i.e.…”

“…Pea (Pisum sativum L. cv Alderman) seedlings were grown in wet vermiculite in complete darkness and handled under dim green light as described previously (7). Except as noted, seedlings 6 to 8 cm tall (second internode stage, 6-7 d old) were selected for experimentation.…”

Quantification of Apoplastic Potassium Content by Elution Analysis of Leaf Lamina Tissue from Pea (Pisum sativum L. cv Argenteum)

“…In addition, changes in the amount of fixed negatively charged sites will alter the apoplastic K+ content at which the buffering capacity of the Donnan phase is lost. As noted by Freudling et al (8) (4,15). The ultimate effect of volume on the K+ concentration within the solution phase, however, will be a function of the net apoplastic K+ content relative to the cation exchange capacity of the cell wall (Fig.…”

Water potential, turgor and cell wall properties in elongating tissues of the hydrotropically bending roots of pea (Pisum sativum L.)

“…Therefore, the hydraulic conductance from the xylem to the elongating cells might be responsible for the difference in water transport between the tissues at high and low atmospheric humidities. However, it is still unknown whether it is the cell membrane of the elongating cells (Nonami & Boyer 1990b;Boyer 1993) or the path from the xylem to the apoplast of elongating cells (Cosgrove & Cleland 1983;Pritchard 1994) that restricts the transport of water from the xylem to the elongating cells.…”