No abstract

NaCl was added to the nutrient solution of 4-6-week old Mesembryanthemum crystallinum plants so that the concentration rose by 50 mM per day. Ten to fifteen days after a concentration of 400 mM was reached, pronounced diurnal oscillations of malate levels indicated that plants had changed from C-photosynthesis to crassulacean acid metabolism (CAM). Due to the NaCl-treatment the solute potential (Ψ) decreased from about -6 bar to -25 bar, and the water potential (Ψ) changed from about -5 bar to -23 bar on average. Ψ showed small diurnal oscillations both in controls and NaCl-treated plants, with an amplitude of 1 to 3 bar, the value at the end of the dark phase being less negative than that at the end of the light phase. Changes of ion levels due to the NaCl-treatment were average increases in Na and Cl from 10-20 to 370-470 mmol kg FW and from below 10 to 280-325 mmol kg FW, respectively, and a decrease in K from 70-80 to 25 mmol kg FW. These changes of ion levels corresponded very closely to an increase of dry weight in per cent of fresh weight observed during the NaCl-treatment (e.g. a change of 2% in one experiment), and osmotically they matched the measured change in Ψ (e.g. about 18-20 bar in one experiment).Most of the organic solutes analysed did not show any significant changes as a result of the NaCl-treatment. The following compounds were identified within the respective ranges of concentrations: mannitol (0.2 to 0.5 mmol kg FW), sum of quaternary ammonium compounds (60 to 140 mg kg FW), choline (0.1 to 0.4 mmol kg FW), betaine (0.3 to 0.7 mmol kg FW), hexoses (2-9 mmol kg FW), pentoses (1-5 mmol kg FW) and sucrose (2-4 mmol kg FW). The levels of proline and of total amino acids minus proline rose during the NaCl-treatment from 0.1-1 mmol kg FW to 2.5-5 mmol kg FW and from 2.5-4 mmol kg FW to 6-8 mmol kg FW, respectively.The changes of Ψ and Ψ, and of Na- and Cl-levels were complete, and new steady levels were attained by the time 400 mM NaCl was reached in the nutrient solution, i.e. many days before pronounced diurnal malate oscillations indicated that the change from C-photosynthesis to CAM had occurred. The attainment of new steady levels of proline and K, however, was much slower and coincided with the onset of CAM.

No abstract

The interrelationships of leaf diffusive conductance, tap root eell turgor pressure and the diameter of the tap root of sugarbeet were studied. The study was eondueted on well-watered plants growing iti pots under artifieial light in the glasshouse. In a typical expet-itnent, on illumination (400 //mol tn"^ s ') leaf conductatice increased frotn 0,6 to 7,4 tntn s"'. Cell tut-gor ptessute in the tap root dect-eased frotn 0,8 MPa to 0,45 MPa and the root diatneter (9.0 ctn) contracted by 145 /an. Removal of light t-esulted in the t-evet-sal of each of the above patatnetet-s to their ptevious values, Quantitively sitnilar t-esults were obtained when sugar beet plants were uprooted and the tesponse of each of the paratnetets was tneasured. The sequence of events however was diffetent. On stitnulation by light, changes in leaf diffusive eonduetanee preceded the turgor and root diameter changes (whieh were simultaneous) by some 15-20 min. In eontrast, on uprooting the simultaneous ehanges in root turgor pressure and diameter preeeded the changes in leaf conductance. The lag titnes between changes in diffusive eonduetanee and turgor pressure in the root were between 20 and 30 min.Tap root turgor pressut-e and diameter correlated strongly and pertnitted the calculation of an apparent whole t-oot volutnett-ic elastic tnodules (55-63 MPa). The stnall changes in tissue volume relative to the transpitation rate suggest that the tap root is not a significant sout-ce of transpit-ational water during the day.