A municipal solid-waste bottom slag was used to grow maize plants under various abiotic stresses (high pH, high salt and high heavy metal content) and to analyse the structural and chemical adaptations of the cell walls of various root tissues. When compared with roots of control plants, more intensive wall thickenings were detected in the inner tangential wall of the endodermis. In addition, phi thickenings in the rhizodermis in the oldest part of the seminal root were induced when plants were grown in the slag. The role of the phi thickenings may not be a barrier for solutes as an apoplastic dye could freely diffuse through them. The chemical composition of cell walls from endodermis and hypodermis was analysed. Slag-grown plants had higher amounts of lignin in endodermal cell walls when compared to control plants and a higher proportion of H-type lignin in the cell walls of the hypodermis. Finally, the amount of aliphatic suberin in both endo- and hypodermal cell walls was not affected by growing the plants on slag. The role of these changes in relation to the increase in mechanical strengthening of the root is discussed.

The distribution of the phytohormone, abscisic acid (ABA), within the phylum ofPhycophyta was investigated by an enzyme-linked immunoassay (ELISA). Of 64 algal species tested (originating from 9 divisions, 20 classes and 36 orders, including procaryotes) all species contained ABA, whereas no ABA could be detected in the bacteria Escherichia coli, Rhodospirilhm rubrum, and Halobacterium halobium. It is concluded that ABA is universally distributed within the algal kingdom and is not restricted to cormophytes. The ability to synthesize ABA must have been developed even within the procaryotes. The physiological role of ABA in some selected algae was studied by investigating 1. the distribution of ABA between the cells and the culture medium, 2. the responses of endogenous ABA to stress, 3. the synthesis of 14C-ABA from externally applied ''C-mevalonic acid, 4. the metabolism of ABA, 5. the effect of externally applied ABA on various physiological reactions of the algae, and the effect of norflurazon on ABA content. ''C-mevalonic acid served as precursor of 14C-ABA synthesis in Dunaliella cells and ABA was metabolised to the same products which have been observed in higher plants. In D. parva the internal ABA level increased upon hyperosmotic salt shocks, and in D. acidophila upon alkalization of the medium. Norflurazon caused an increase of ABA content in Dunaliella. Externally applied ABA did not affect photosynthesis, respiration and K' content of the cells. The permeability of the plasma membrane of D. acidophila to water was slightly decreased by ABA. The possible physiological function of ABA in algae is discussed.Botanica Acta 102 (1989) 326-334 -

Photosynthesis, stroma-pH, and internal K' and Cl-concentrations of isolated intact chloroplasts from Spinacia okracea, as well as ion (K+, H+, Cl1) movements across the envelope, were measured over a wide range of external KCI concentrations (1-100 millimolar).Isolated Intact chloroplasts are surrounded by a double membrane, the chloroplast envelope, the inner membrane of which forms a barrier between the stroma space and the external medium. Translocation systems located on this inner membrane allow regulation of the internal pools of metabolites (9). Concerning the distribution of inorganic ions, it is not known whether intact chloroplasts are able to maintain a defined ionic milieu independently of the external medium. With reference to proton distribution, it is known that upon illumination the stroma of isolated intact chloroplasts becomes alkaline (13), as a consequence of proton pumping across the thylakoid membrane. This alkalization is not transmitted to the external medium, i.e. stroma alkalization gives rise to a transenvelope proton gradient (13) which determines the ratio of chloroplastic and cytosolic redox-and phosphorylation potentials (9). An alkaline stromapH is a prerequisite for the full activation of pH-dependent Calvin Cycle enzymes (6). Whether or not maintenance of the ' Supported by the Deutsche Forschungsgemeinschaft.transenvelope proton gradient requires H+ export from intact chloroplasts into the medium to compensate for inward diffusion of H+ has been a matter of debate (5,(7)(8)(9)(10)13). In low salt media, intact chloroplasts exhibit a light-induced release of protons and an uptake of K+ (8). With respect to the concentration of monovalent cations, low salt as well as standard media (5-25 mM K+) differ by almost a whole order of magnitude from estimated cytoplasmic concentrations (17). We have tested various chloroplast-characteristics such as photosynthetic activity, stroma-pH, internal concentrations of cations and anions in intact chloroplasts and ion movements across the envelope over a wide range of external ion concentrations (1-100 mM). It is shown that chloroplast properties are markedly influenced by high K+ concentrations in the medium which are comparable to physiological K+ concentrations in the cytosol.

No abstract

The effect of divalent cations on cation fluxes across the chloroplast envelope and on photo­ synthetic reactions of intact spinach chloroplasts was investigated.In the absence of EDTA, divalent cations inhibited photosynthetic CO2-fixation and PGA-reduction at low PGA concentrations, but had almost no effect on the reduction of OAA, BQ, and on PGA-reduction at high PGA concentrations. The inhibitory effect of Ca2+ was greater than that of Mg2+. Inhibition of photosynthesis was greater when the divalent cations were added in the dark than when added in the light. In spite of its inhibitory effect, Mg2+ partially restored the Ca2+ inhibited photosynthesis, indicating the involvement of a Mg2+/Ca2+ antagonism in the inhibitory effect.The inhibitory effect of divalent cations is stronger in a medium with low concentrations of K+ than in the presence of 20 - 50 mᴍ KCl. Mg2+ induced a release of plastidal K+ and an in­ crease of stromal H+ concentration.The results indicate that external Mg2+ in the absence of EDTA does not influence neither photosynthetic electron transport nor photophosphorylation, but inhibits the light activation of some enzymes of the carbon reduction cycle. The latter is assumed to be due to an acidification of the stroma pH and the decrease of endogenous K+ level. Since the chloroplast envelope has only a very low permeability towards Mg2+, possible mechanisms are discussed by which Mg2+ changes the properties of the chloroplast envelope and thus secondarily induces the observed effects.