Implications for cytoplasmic pH,protonmotice force,and amino-acid transport across the plasmalemma of Riccia fluitans

By means of pH-sensitive microelectrodes, cytoplasmic pH has been monitored continuously during amino-acid transport across the plasmalemma of Riccia fluitans rhizoid cells under various experimental conditions. (i) Contrary to the general assumption that import of amino acids (or hexoses) together with protons should lead to cytoplasmic acidification, an alkalinization of 0.1–0.3 pH_c units was found for all amino acids tested. Similar alkalinizations were recorded in the presence of hexoses and methylamine. No alkalinization occurred when the substrates were added in the depolarized state or in the presence of cyanide, where the electrogenic H⁺-pump is inhibited. (ii) After acidification of the cytoplasm by means of various concentrations of acetic acid, amino-acid transport is massively altered, although the protonmotive force remained essentially constant. It is suggested that H⁺-cotransport is energetically interconnected with the proton-export pump which is stimulated by the amino-acid-induced depolarization, thus causing proton depletion of the cytoplasm. It is concluded that, in order to investigate H⁺-dependent cotransport processes, the cytoplasmic pH must be measured and be under continuous experimental control; secondly, neither pH nor the protonmotive force across a membrane are reliable quantities for analysing a proton-dependent process.Abbreviations 3-OMG 3-oxymethylglucose - pH_c cytoplasmic pH - _m electrical potential difference across the respective membrane, i.e. membrane potential - _H+/F (=pmf) electrochemical proton gradient     

Inhibition and promotion by light of the accumulation of translatable mRNA of the light-harvesting chlorophyll a/b-binding protein of photosystem II

The amount of in-vitro translatable mRNA of the light-harvesting chlorophyll a/b-binding protein (LHCP) of photosystem II strongly increases in darkness (D) after a 5-min red-light pulse while continuous illumination of mustard seedlings with far-red (FR), red or white light leads only to a slight increase in the amount of translatable LHCP-mRNA. No increase can be observed after a long-wavelength FR (RG9-light) pulse. However, a FR pretreatment prior to the RG9-light pulse strongly increase LHCP-mRNA accumulation in subsequent D. This is not observed in the case of the mRNA for the small subunit of ribulose-1.5-bisphosphate carboxylase. The increase of LHCP-mRNA in D after a FR pretreatment can be inhibited by a reillumination of the seedlings with FR. The inhibition of LHCP-mRNA accumulation during continuous illumination with FR and the strong increase in D following a FR illumination was found to be independent of chlorophyll biosynthesis since no correlation between chlorophyll biosynthesis and translatable LHCP-mRNA levels could be detected. Even strong changes in the amount of intermediates of chlorophyll biosynthesis caused by application of levulinic acid or 5-aminolevulinic acid did not affect LHCP-mRNA levels. Therefore, we conclude that the appearance of LHCP-mRNA is inhibited during continuous illumination, even though illumination leads to a storage of a light singal which promotes accumulation of translatable LHCP-mRNA in D.Abbreviations c continuous - Chl chlorophyll - D darkness - FR far-red light (3.5 W·m^-2) - LHCP light-harvesting chlorophyll a/b-binding protein of photosystem II - NF Norfluration - PChl protochlorophyll(ide) - Pfr far-red absorbing form of phytochrome - Ptot total phytochrome - R red light (6.8 W·m^-2) - RG9-light long-wavelength FR (10 W·m^-2) - SSU small subunit of ribulose-1.5-bisphosphate carboxylase - WL white light - () Pfr/Ptot=wavelength-dependent photoequilibrium of the phytochrome system     

Internode length in Pisum. Action of gene lw

Jolly, C. J., Reid, J. B. and Ross, J. J. 1987. Internode length in Pisum. Action of gene lw.
Mutant K29 of Pisum sativum L. is shown to possess a recessive gene at a new locus, lw , which results in reduced internode length, delayed flowering and increased symptoms of water congestion compared with the parental cv. Torsdag. The interaction of gene lw with the internode length genes na, le, la and cry ⁵ is examined. Extracts from the shoots of Iw plants are shown to contain similar levels of gibberellin (GA)-like substances to comparable Lw plants, but Iw plants do not elongate to the same extent as Lw plants when treated with GA₁₉ GA₁₉, or GA₂₀. The effect of gene Iw is not graft-transmissible. Unlike essentially isogenic dwarf lines possessing the GA-synthesis genes le, Ih or Is, lw plants show a relative increase in elongation similar to Torsdag in response to photoperiod extensions from sources rich in far-red light. These results suggest that gene lw probably does not reduce elongation by influencing GA-synthesis and that the response to photoperiod extensions with far-red light may depend on the level of GA.     

Ionic balance,proton efflux,nitrate reductase activity and growth ofHippophaë rhamnoides L. ssp.rhamnoides as influenced by combined-N nutrition or N2 fixation

Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N₂ fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH ₄ ⁺ , a mixture of NH ₄ ⁺ and NO ₃ ^? producing the highest yields. Growth was severely reduced when solely dependent on N₂ fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N₂-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO ₃ ^? dependent plants was almost entirely located in the roots. However, when grown with a combination of NO ₃ ^? and NH ₄ ⁺ , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH ₄ ⁺ , NO ₃ ^? contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO ₃ ^? +NH ₄ ⁺ plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH ₄ ⁺ plants than in the NO ₃ ^? plants. Measured extrusions of H⁺ or OH^? (HCO ₃ ^? ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N₂ fixation amounted to 0.45–0.55 meq H⁺. (mmol N_org)^?1. Without acidity control and in the presence of NH ₄ ⁺ , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N₂-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites.     

The effect of lime on phosphorus adsorption and barley growth in three acid soils

For three acid soils from Santa Catarina, Brazil, lime application and time of incubation with lime had little effect on the adsorption of added phosphorus. In two soils with high contents of exchangeable aluminium, solution P and isotopically exchangeable P were decreased by incubating with lime for 1 month: phosphorus was probably adsorbing on freshly precipitated aluminium hydrous oxides. In one soil with less exchangeable aluminium, P in solution was increased by liming. After 23 months lime increased solution and exchangeable P possibly due to crystallization of aluminium hydrous oxides reducing the number of sites for P adsorption. All these changes were however small. In a pot experiment, lime and phosphorus markedly increased barley shoot and root dry matter and P uptake. Although liming reduced P availability measured by solution P, isotopically exchangeable P and resin extractable P, it increased phosphorus uptake by reducing aluminium toxicity and promoting better root growth. The soil aluminium saturation was reduced by liming, but the concentration of aluminium in roots changed only slightly. The roots accumulated aluminium without apparently being damaged.     

A comparative study of ammonium toxicity at different constatn pH of the nutrient solution

Seedlings of 14 species were grown for 14–28 days on nutrient solution with 6 mmol.l⁻¹ NH₄ as the sole nitrogen source. Solutions acidity was were kept constant at pH 4.0, 5.0, 6.0 and 7.0 by continuous titration with diluted KOH. The following species were used: barley, maize, oats sorghum, yellow and white lupin, pea, soybean, carrot, flax, castor-oil, spinach, sugarbeet and sunflower. Most plant species grew optimally at pH 6.0 with slight reductions at pH 5.0. Growth of many species was severely inhibited at pH 4.0, but this inhibition was not observed with the legume and cereal species. Yield depressions at pH 4.0 relative to pH 6.0 were well correlated with the respective relative decreases of the K concentration in their roots (P<0.002). In the roots of two species (sunflower and flax) total N concentrations were also strongly reduced at pH 4.0. apparently, the interactions between uptake of K, NH₄ and H ions become the prevalent problem at suboptimal pH. At pH 7.0, yields were also considerably decreased, with the exception of the lupines. At this pH, the roots of the growth inhibited plants were characterized by increased levels of total N and free NH₄. It is thought that the binding capacity of the roots for NH₄ is an important factor in preventing NH₄/NH₃ toxicity at supraoptimal pH.     

Competition between Dunaliella species at high salinity

Information on the distribution of more than 225 species of planktonic, periphytic, and benthic rotifers from diverse waters in south and central Sweden was analyzed for pH preference. No particularly strong correlation was found between pH and any other environmental factor, with regards to rotifer distribution. However, species indicating oligotrophy generally have their pH optima at or below 7.0, while those indicating eutrophy occur at or above this level. Rotifers found in acidic waters are often non-planktonic or semiplanktonic.