Solute vacuolar

Betalains are vacuolar plant pigments. Hence their hydrophilic nature is comprehensible. Although they are slightly soluble in ethanol and methanol, water is the best snited solvent both for stability and solnbility reasons. In contrast to the antho-cyanins, the betalains are even more polar as can be demonstrated by shorter retention times in RP-HPLC and lower solubilities in alcoholic solutions. The varying polarities may also be beneficially used to separate anthocyanins from betalains on an RP-18 solid-phase extraction cartridge (Stintzing, unpublished data). 

Lazzaro MD, Thomson WW. The vacuolar-tubular continuum in living trichomes of chickpea (Cicer arietinum) provides a rapid means of solute delivery from base to tip. Protoplasma 1996 193 181-190. 

Anthocyanins are the most common water-soluble pigments in the plant kingdom, and are normally found dissolved uniformly in vacuolar solutions of epidermal cells. However, in cases like the Sphagnorubins, the pigments are so tenaciously bound to the cell wall that they are only extracted with difficulty. 

Returning once again to the questions of function and uses, the old concept of flavonoids being merely the by-products of cellular metabolism, which are simply compartmentalized in solution in the cell vacuole, is well and truly past its use-by date. For a start, studies have revealed that flavonoids are also commonly found on the outer surfaces of leaves and flowers, albeit only the aglycone form. Additionally, flavonoids have been shown over the past few years to be found in the cell wall, the cytoplasm, in oil bodies, and associated with the nucleus and cell proteins, as well as in the vacuole. Even in the vacuole, flavonoids are not necessarily found free in solution. For example, protein-bound flavonoids have been isolated from lisianthus and other flowers in which a structurally specific binding has been identified (in anthocyanic vacuolar inclusions). It is probable that flavonoid location and specific protein binding properties will ultimately prove to relate directly to their function in plants. 

Rohrbach, P., Sanchez, C. P., Hayton, K., Friedrich, O., Patel, J., Sidhu, A. B., Ferdig, M. T., Fidock, D. A., and Lanzer, M. (2006). Genetic linkage of pfmdrl with food vacuolar solute import in Plasmodium falciparum. EMBO. 25, 3000-3011. 

Fig. 81. Vacuolar transformation of the endoplasmic reticulum in the apical region of a type 2 Clara cell from a ca. 235 g female rat (breeder Winkelmann, Borchen-Kirchborchen) treated for 5 days per week with 125 mg dexpanthenol in a 5 % aqueous solution (Bepanthen) per kg body weight X day from April 17 to August 14, 1967 for a total of 82 days. Fixed on August 14, 1967 under methitural anaesthesia by intratracheal instillation of 2.5 % glutaraldehyde in phosphate buffer (pH 7.4) before opening the thorax. After washing in phosphate buffer the tissue was postfixed with 1 % osmium tetrox-ide in phosphate buffer for 2 h. Contrasted en bloc for 12 h with 0.5 % uranyl acetate in 70 % ethanol. Embedded in a 2 8 mixture of methyl and butyl methacrylate. Sectioned at 50 nm. Lead citrate after Reynolds (1963). Plate 9/07...

Anthocyanins are present in different plant organs, such as fruits, flowers, stems, leaves, and roots [16]. These pigments are normally found dissolved uniformly in the vacuolar solution of epidermal cells. However, in certain species, the anthocy-anins are localized in discrete regions of the cell vacuole, called anthocyanoplasts [17]. The main sources of anthocyanin (Table 58.1) are red fruits, maiifly berries and red grapes cereals, principally purple maize and red-purple and vegetables such as eggplant [6, 18]. 

Minet, M., Dufour, M.-E. and Lacroute, F. (1992) Complementation of Saccharomyces cerevisiae auxotrophic mutants by Arabidopsis thaliana cDNAs, Plant J. 2, 417-422. Hamamatsu, S., Shibuya, I., Takagi, M. and Ohta, A. (1994) Loss of phosphatidylserine synthesis results in aberrant solute sequestration and vacuolar morphology in Saccharomyces cerevisiae, FEBS Lett. 348, 33-36. 

Martinoia, E., Massonneau, A. Frangne, N. (2000). Transport processes of solutes across file vacuolar membrane of higher plants. Plant Cell Physiology, 41,1175-1186. 

Their data showed that the loss of malic acid from the vacuole depended strongly on the water potential of the external medium which varied due to different concentrations of sorbitol. Substantial efflux of malic acid from the vacuole was achieved at high water potential of the medium, and the export of malic acid decreased if the water potential of the medium was lowered. Malic efflux from the vacuole was lowest when the vacuolar content and the external solution were isotonic. 

Table II - Appearent activation energies in water exchange between vacuolar fluid and extracellular solution in living and heat-killed Valoniae. Values of activation energies for self diffusion of water (35,36) and for thermodialysis of water through artificial porous partitions are included for comparison.

The vacuoles in higher plants are essential for the maintenance and regulation of the homeostatic environment of the cells [1]. The vacuolar membranes of plant cells contains an electrogenic H -ATPase which provides the proton-motive force for the active transport of solutes across the vacuolar membranes. The activities of certain membrane-bound enzymes are lost by the removal of constituted lipids, but are restored after the addition of exogenous phospholipids [2,3]. Kasamo [4] showed that the various molecular species of PC activated to different extents the H -ATPase solubilized from the plasma membrane of rice cultured cells. 

We now wish to focus our attention on the parameter (J /P)h+. From Tables 2 and 3, it is apparent that its value remains smaller than that of the parameter of all other ions. Some salient features of (J /P)h+ can be derived from some of our earlier calculations 23, They show that at fixed external conditions and internal pH, there are no marked effects of the internal variables and of Em on (Ja/p)h+, although the other parameters (Ja/p)i required to find back the internal conditions are changing. Conversely, at fixed internal conditions and external pH, the value of (Ja/P)h+ is also only weakly affected by changes of the external conditions. Finally, if all external and internal conditions are kept constant (Ja/p)h+ varies appreciably with the external pH in acid solutions (pH < 7). It is reasonable to conclude from all these facts that the role of the proton transfer in the course of the ionic transfer process between the external and internal phases is restricted to the cytoplasmic and vacuolar pH regulation. The proton transfer exerts a minor effect on the other internal parameters. 

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