�ber Zusammenh�nge zwischen dem CO2-Austausch und der Abgabe von Wasserdampf durch Bryophyllum daigremontianum Berg

116

Acid metabolism and gas exchange studies were conducted in situ on the cactus Opuntia basilaris Engelm. and Bigel. A pattern of significant seasonal variation was evident. The pattern was controlled by rainfall, which significantly influenced plant water potentials, total gas transfer resistances, and nocturnal organic acid synthesis. In winter and early spring, when plant water stress was mild, stomatal and mesophyll resistances remained low, permitting enhanced nocturnal assimilation of "CO2. The day/night accumulation of acidity was large during these seasons. In summer and fall, plant water stress was moderate, although soil water stress was severe. The nocturnal assimilation of "CO2 was very low during these seasons, even in stems with open stomata, indicating large mesophyll resistances restricting exogenous gas incorporation. The day night accumulation of acidity was reduced, and a low level of acid metabolism persisted throughout this period. The rapid response to a midsummer rainfall emphasizes the importance of plant water potential as a parameter controlling over-all metabolic activity. The seasonal variations of acid metabolism and gas exchange significantly influenced the efficiency of water use and carbon dioxide assimilation. Periods of maximal efficiency followed rainfall throughout the course of the year.Historically, succulents have been considered a group of plants with morphological and anatomical similarities, and recently this classification has been expanded to include physiological similarities (7,16

Section: Methodsmentioning

confidence: 99%

Seasonal Patterns of Acid Metabolism and Gas Exchange in Opuntia basilaris

Szarek¹,

Ting²

1974

116

“…2) consists of a microcapillary (tip diameter: [3][4][5][6][7] ,um) filled with silicone oil and connected to a small pressure chamber containing a pressure transducer. When the microcapillary tip is introduced into a cell, the cell P pushes the oil back into '1 .…”

mentioning

confidence: 99%

“…These processes should follow diffusion kinetics, whereas the pressure-relaxation of individual cells measured by the probe is exponential and yields T,I2 (see Fig. 3 and equation 1 In fact, it can be calculated from gas-exchange curves in the literature (6,8,9) (23)(24)(25) and other plants (14) suggests even more that water relations are an important factor. However, Winter and Luttge (24) observed that, during the induction of CAM in M. crystallinum by high salinity (NaCl), the succulence of the leaves was reduced and the water content decreased.…”

mentioning

confidence: 99%

Water-relation Parameters of Individual Mesophyll Cells of the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana

Steudle

Smith²,

Lüttge³

1980

130

Water-relation parameters of leaf mesophyll cells of the CAM plant Kaklchoi daigremontiana have been determined directly in cells of tissue slices using the pressure-probe technique. Turgor pressures measured in cells of the second to fourth layer from the cut surface showed an average of 1.82 ± 0.62 bar (mean ± SD; n = 157 cells). This was lower than expected from measurements of the osmotic pressure of the cell sap. The half-time (T112) for water-flux equilibration of individual cels was 2.5 to 8.8 seconds. This is the fastest T112 found so far for higher-plant cells. The calculated values of the hydraulic conductivity were in the range of 0.20 to 1.6 x 10-5 centimeters second-' bar-', with an average of (0.69 ± 0.46) x 10-5 centimeters second`bar-' (mean + SD; n = 8 cells). The T1/2 values of water exchange of individual cells are consistent with the overall rates of water-flux equilibration measured for tissue slices.The volumetric elastic moduli (e) of individual cells were in the range 13 to 128 bar for turgor pressures between 0.0 and 3.4 bar, the average e value was 42.4 ± 27.7 bar (mean ± SD; n = 21 cells). This e value is similar to that observed for other higher-plant cells.The of CO2 fixation during the dark period (e.g. refs. 3, 12, 13, 22). However, it is not clear whether the occurrence of CAM is associated with particular water-relation parameters of CAM-performing cells, such as the turgidity of cells, the water permeability of cell membranes and the elastic extensibility of cell walls.The osmotic processes that occur during the CAM rhythm may be rate-limited at different levels, ie. at the level of either solute (malic acid) or water transport, of solute synthesis and degradation, or by the mechanical extensibility of solute-and waterstoring cells (18). Interrelations may occur (8) between waterrelation characteristics of CAM-performing cells and (a) intracellular (tonoplast) transport of malic acid (10, 11), (b) synthesis and degradation of malate in the cytoplasm, and (c) the rhythm of stomatal movement. At the morphological level, CAM seems only to be found in tissues possessing voluminous cells containing chloroplasts and large vacuoles. As a consequence, the plant organs containing these tissues are normally "succulent," but it has proved hard to formulate a satisfactory definition of "succulence" from a physiological and biophysical point of view.For a decision as to whether plant water status plays a key role in the induction and control of CAM, the water-relation parameters2 (i.e. cell P, water-exchange rates (T1/2 values), Lp and e) of individual cells must be known. Such measurements have become possible with the introduction of the pressure-probe technique, which was developed first for giant algal cells (17,19,21,27)

“…Under water stress conditions, salt-deprived plants using only the reductive pentose phosphate cycle pathway assimilated less carbon and were less efficient in their water use than salt-treated plants using predominately the CAM pathway. These results support the hypothesis that the ability to use the CAM pathway reduces the capacity for reductive pentose phosphate cycle fixation but permits higher productivity in water-limited environments.In plants exhibiting the CAM pathway of carbon fixation, the relative amounts of CAM and C33 used for external CO2 assimilation may vary with water availability (1,10,15,27), day-night temperature differentials (11, 26), or photoperiod (16). Generally, conditions which increase water stress favor CAM because the water use efficiency of CAM is greater than that of C3 (17).…”

mentioning

confidence: 99%

“…relative amounts of CAM and C33 used for external CO2 assimilation may vary with water availability (1,10,15,27), day-night temperature differentials (11,26), or photoperiod (16). Generally, conditions which increase water stress favor CAM because the water use efficiency of CAM is greater than that of C3 (17).…”

mentioning

confidence: 99%

Salt Requirement for Crassulacean Acid Metabolism in the Annual Succulent, Mesembryanthemum crystallinum

Bloom

1979

In experiments with the facultative Crassulacean acid metabolism (CAM) species, Mesembryanthemum crystailinum, only plants which received high levels of inorganic salts fixed substantial amounts of CO2 by the CAM pathway. Equivalent osmolarities of polyethylene glycol 6000 did not yield any CAM fixation. Plant water potential and turgor pressure had no detectable influence on the amount of CAM fixation. These observations rule out the possibility that the inorganic ions were acting as osmotic agents.Carbon dioxide and water exchange analysis showed that when water supply was not limiting, salt-deprived plants sustained higher reductive pentose phosphate cycle carbon fixation rates than salt-treated plants. Under water stress conditions, salt-deprived plants using only the reductive pentose phosphate cycle pathway assimilated less carbon and were less efficient in their water use than salt-treated plants using predominately the CAM pathway. These results support the hypothesis that the ability to use the CAM pathway reduces the capacity for reductive pentose phosphate cycle fixation but permits higher productivity in water-limited environments.In plants exhibiting the CAM pathway of carbon fixation, the relative amounts of CAM and C33 used for external CO2 assimilation may vary with water availability (1,10,15,27), day-night temperature differentials (11, 26), or photoperiod (16). Generally, conditions which increase water stress favor CAM because the water use efficiency of CAM is greater than that of C3 (17).Mesembryanthemum crystallinum shifts from primarily C3 fixation to primarily CAM fixation after a few days' exposure to high salt concentrations (23).This effect of high salt has been viewed as a result of increased osmotic stress (25). This species accumulates very large quantities of salt even when given unlimited access to nonsaline water (20, 23). This accumulation suggests a metabolic requirement for high levels of inorganic ions. In the following study, M. crystallinum was unable to sustain significant CAM fixation when salt levels in the growth medium were restricted. Moreover, the salt requirement for CAM provided an opportunity for comparing within a single population the relative merits of C3 and CAM fixation. (8). In nutrient solution culture, high levels of water stress are difficult to achieve without resorting to osmoticums. For these reasons, the selected growth medium consisted of equal parts potting soil and sand and the selected method for producing water stress was water deprivation. MATERIALSThe plants were grown in an environmental chamber with 12-h day-night cycle, 25 C days and 15 C nights, 12 C dew point day and night, and a light intensity of 46 nE cm-2 s-' PAR. These growth conditions are typical of M. crystallinum's natural habitat and were found to favor CAM (3).Watering and Experimental Treatments. The protocol for watering the plants ( Fig. 1) was that all plants received identical treatment but for a relatively short period. The initial 2-week drought period was to in...