Beweis f�r die Beteiligung von beweglichen Transportstrukturen (Tr�gern) beim Ionentransport durch pflanzliche Membranen und die Kinetik des Anionentransports bei Elodea im Licht und Dunkeln

Abstract

Influx and efflux of anions in leaves of Elodea canadensis were investigated. A major component of phosphate efflux was found to be a function of the external phosphate concentration in accord with saturation kinetics, i.e. it was found to be proportional to phosphate influx. This suggests that the transport structures which mediate ion transport in plant membranes are mobile and can work in both directions (Fig. 7C). The higher the external concentration the more bound ions (A b (-) , Fig. 7C) are exchanged for external ions (A a (-) ) instead of being transported back to the inside of the membrane. Thus it was demonstrated that ion transport in plants is mediated by carriers or transportases. The action of the carriers is supported by ATP or another "energy-rich" compound which is regenerated by ATP; ATP may be supplied by the mitochondria or/and chloroplasts. In line with these findings some transport phenomena exhibited features of coenzyme kinetics.Magnitude and molecular nature of the carrier motion are unknown. There is no evidence for rotating or shuttling monovalent carriers. The carriers may be polyvalent and may be part of bigger structural units within the membrane. Nevertheless, these experimental observations are rather consistent with the idea that plant membranes contain tertiary or quarternary formed proteins or lipoproteins than with the conventional lipid bilayer models of cell membranes.

Kinetics and Energetics of Light-enhanced Potassium Absorption by Corn Leaf Tissue

“…Algal eellts have been used (22,23,34) and virtuallly identical resullts were reported when these inhibitors were emnployed in light-dark treatments. Also similar resuilts have been repor'ted for tissues of aquatic angiosperms, tissues more highily organized than those o'f ailgae (21,41,42).…”

Photophosphorylation In Vivo

“…This leads to the assumption that the respiratory source of ATP is sufficient for sulfate influx in the light (188). Only in those cases in nitrogen in which DCMU was ineffective, as has been shown in Elodea canadensis (270), and if uncouplers are effective, the sulfate influx may be supplied by cyclic PP. But so far a fi nal proof has not been established.…”

“…With increasing concentrations of mannitol in the incubation medium the ATP level and also the sulfate infl ux in Elodea canadensis leaves decrease (270). In Limnophila the inhibition of the sulfate as well as of the phosphate infl ux by CCCP is parallel to the decrease of the ATP level (166).…”

“…Likewise, the activity of enzymes is directly or indirectly changed by light which in this way may infl uence ion uptake. (32,86) and this phosphate uptake is also enhanced by light (71,100,215,270). Calculations based upon the internal concentration of phosphate and the electrical potential difference of the membrane of Nitella translucens (215) as well as Elodea de nsa (100) revealed that in addition to the strong dependence of the influx on temperature and light in a special range of the phosphate concentration in the medium, phosphate uptake is an energy-de pendent active process.…”

ACTION SPECTRA FOR PHOTOSYNTHESIS AND LIGHT‐STIMULATED ION TRANSPORT PROCESSES IN HYDRODICTYON AFRICANUM

“…The results of Jeschke (1967) and of Weigl (1967) suggest that, in Flodea 6o J. A. RAVEN densa and E. canadensis, light-stimulated active Cl influx can be supported by cyclic photophosphorylation.…”