Day/night variations in turgor pressure in individual cells of Mesembryanthemum crystallinum L.

Abstract

Using a pressure probe, turgor pressure was directly determined in leaf-mesophyll cells and the giant epidermal bladder cells of stems, petioles and leaves of the halophilic plant Mesembryanthemum crystallinum. Experimental plants were grown under non-saline conditions. They displayed the photosynthetic characteristics typical of C-plants when 10 weeks old and performed weak CAM when 16 weeks old. In 10 week old plants, the turgor pressure (P) of bladder cells of stems was 0.30 MPa; of bladder cells of petioles 0.19 MPa, and of bladder cells of leaves 0.04 MPa. In bladder cells from leaves of 16 week old plants, marked changes in turgor pressure were observed during day/night cycles. Maximum turgor occurred at noon and was paralleled by a decrease in the osmotic pressure of the bladder cell sap. Similar changes in the cell water relations were observed in plants in which traspirational water loss was prevented by high ambient relative humidity. Turgor pressure of mesophyll cells also increased during day-time showing macimum values in the early morning. No such changes in turgor pressure and osmotic pressure were observed in bladder and mesophyll cells of the 10 week old plants not showing the diurnal acid fluctuation typical of CAM.

Carbon Dioxide and Water Demand: Crassulacean Acid Metabolism (Cam), a Versatile Ecological Adaptation Exemplifying the Need for Integration in Ecophysiological Work

“…5; , for leaves of the atmospheric bromeliad Tillandsia recurvata (Fig. 6) and by another group for leaves of M. crystallinum (Rygol et al, 1986). Turgor was found to increase gradually during the dark period, towards the end of the dark period or just after stomatal closure, allowing retention of water as the light period commenced.…”

Growth and development of Mesembryanthemum crystallinum (Aizoaceae)

“…The data suggest that EBC not only store salt (Lu$ ttge et al, 1978) but also act as water reservoirs, accommodating changes in osmotic pressure in the mesophyll cells throughout the day-night cycle (Ruess & Eller, 1981 ;Rygol et al, 1986Rygol et al, , 1989Lu$ ttge, 1993). Such changes might arise indirectly through transpiration driven by environmental conditions, or directly, as a result of malic acid accumulation and decarboxylation associated with CAM activity.…”

Nuclear-magnetic-resonance imaging of leaves ofMesembryanthemum crystallinum L. plants grown at high salinity

“…The conclusion that water is apparently more bound in this mesophyll cell type than in other ones has important consequences for the interpretation of the water relations of the leaf of this plant. Rygol et al (1986Rygol et al ( , 1988 have recently studied the day-night rhythm in the turgor pressure of individual mesophyll cells and in single bladder cells of the upper and lower epidermes of salt-treated M. crystallinurn plants by using the pressure probe (Zimmermann et al 1969;Steudle and Zimmermann 1971;H/isken et al 1978;Zimmermann 1978Zimmermann , 1988. As a consequence of malate accumulation in the mesophyll cells during the night and the subsequent degradation of this compound, a maximum in turgor pressure is recorded in the mesophyll cells at the beginning of the light period (06.00 h).…”

“…Excision of the leaf had no significant effects on the water status of the tissue since N M R measurements over several hours did not show any change in the contrast of the images. In addition, turgor-pressure measurements in individual cells of the leaf (by means of the pressure probe) revealed constant turgor pressure (data not shown; see also Rygol et al 1986Rygol et al , 1989Zimmermann et al 1980). Evaporation effects during the experiments could therefore be excluded.…”

“…The lower and upper epidermes of the leaf of this plant are covered by bladder cells which have a volume between 0.05 mm 3 and 0.8 mm 3. From pressure-probe measurements it is known that these large bladder cells function as water-exchange reservoirs during the malate accumulation and degradation which occurs in the much smaller mesophyll cells (average volume 0.7.10 3 mm3; Steudle et al 1975;Rygol et al 1986Rygol et al , 1989; Zimmermann 1988). Moreover, there is evidence that the water exchange predominantly occurs between the mesophyll cells and the bladder cells of the upper epidermis, but not between those of the lower epidermis.…”