The relationship between phosphate status and cyanide-resistant respiration in bean roots

Bean ( Phaseolus vulgaris L.) seedlings were cultured on complete or phosphate-deficient nutrient medium. After 14 days of culture on phosphate-deficient medium the visible symptoms of P_i deficiency were observed only in the shoot, the fresh and dry weights of the roots were slightly higher than in control plants. The decreased P_i content in the roots had little effect on total respiration rate but had an effect on the level of inhibition of respiration by cyanide. The high resistance of respiration to cyanide observed in P_i-deficient roots was the result of the suppression of cytochrome path activity and an increased participation of the alternative, cyanide-resistant pathway. The cytochrome pathway activity increased when inorganic phosphate was supplied to P_i-deficient roots for 1 or 3.5 h. It is speculated that the suppression of cytochrome pathway in P_i-deficient roots may result from restriction of the phosphorylating capacity or a partial inhibition of cytochrome oxidase activity.     

Oxidation of NADH by plant mitochondria: Kinetics and effects of calcium ions

The kinetics of NADH oxidation by the outer membrane electron transport system of intact beetroot (Beta vulgaris L.) mitochondria were investigated. Very different values for V_max and the K_m for NADH were obtained when either antimycin A-insensitive NADH-cytochrome c activity (V_max= 31 ± 2.5 nmol cytochrome c (mg protein)^?1 min^?1; K_m= 3.1 ± 0.8 μM) or antimycin A-insensitive NADH-ferricyanide activity (V_max= 1.7 ± 0.7 μmol ferricyanide (mg protein)^?1 min^?1; K_m= 83 ± 20 μM) were measured. As ferricyanide is believed to accept electrons closer to the NADH binding site than cytochrome c, it was concluded that 83 ± 20 μM NADH represented a more accurate estimate of the binding affinity of the outer membrane dehydrogenase for NADH. The low K_m determined with NADH-cytochrome c activity may be due to a limitation in electron flow through the components of the outer membrane electron transport chain. The K_m for NADH of the externally-facing inner membrane NADH dehydrogenase of pea leaf (Pisum sativum L. cv. Massey Gem) mitochondria was 26.7 ± 4.3 μM when oxygen was the electron acceptor. At an NADH concentration at which the inner membrane dehydrogenase should predominate, the Ca²⁺ chelator, ethyleneglycol-(β-aminoethylether)-N,N,-tetraacetic acid (EGTA), inhibited the oxidation of NADH through to oxygen and to the ubiquinone-10 analogues, duroquinone and ubiquinone-1, but had no effect on the antimycin A-insensitive ferricyanide reduction. It is concluded that the site of action of Ca²⁺ involves the interaction of the enzyme with ubiquinone and not with NADH.     

The effect of chlorophyll content on changes of photochemical reactions in intact kidney bean leaves

Abstract. Activation spectra of photochemical reactions were measured by a flash spectrophotometer in leaves having varying chlorophyll contents at different stages of greening. The increase of chlorophyll concentration up to 30 nmol cm^-2 elevated the rates of photochemical reactions at all wavelengths of light used, and was found to be produced by an increase in the amounts of reaction centres. Further accumulation of chlorophyll up to 40 nmol cm^-2 was associated with an increase in light-harvesting chlorophyll, an improved rate of photochemical reactions around 600 nm and at 700 nm, and self-absorption and screening effects where chlorophyll absorbed maximally (400–450 nm and around 680 nm).     

Poly(γ-glutamylcysteinyl)glycines or phytochelatins and their role in cadmium tolerance of Silene vulgaris

Abstract. The effect of cadmium on growth of Cd-tolerant and -sensitive plants of Silene vulgaris and on the production of metal-binding compounds in both types of plants was studied. The Cd-content of the roots and the Cd-root/shoot ratio was higher in Cd-tolerant plants. A Cd-binding compound (Cd-BC) with an apparent molecular mass of 14.5 kD was isolated from the roots of Cd-tolerant and -sensitive plants, grown in 40 mmol m⁻³ Cd for 21 d. More than 60% of the total Cd in the roots was associated with this compound. Determination of the amino-acid content of the purified Cd-containing compound from both types of plants showed that they possessed a similar amino-acid composition to that of phytochelatins. Only the bis- and tris-forms were present. The amount of Cd and sulphide associated with phytochelatin was greater in tolerant plants than in sensitive ones suggesting that an increased sulphide content of complexes containing peptide, sulphide and Cd may form the basis of evolved Cd-tolerance in Silence vulgaris.     

An automated greenhouse sand culture system suitable for studies of P nutrition

Abstract. Maintenance of realistically low solution P concentrations under controlled conditions is a major difficulty in studies of P nutrition. In this report, we describe a relatively simple and economical sand culture system capable of sustaining plant growth to maturity under controlled yet realistic P regimes. The system uses Al₂O₃ as a solid-phase P buffer, and modern process control technology to control irrigation and addition of other mineral nutrients. Aspects of the design, use and potential applications of automated solid-phase systems are discussed. The system was used to grow Phaseolus vulgaris to matarity at 0.4 mmol m³, 1.0 mmol m³ and 27 mmol m³ P with and without mycorrhizal inoculation. At flowering, low solution P concentrations were associated with reduced leaf concentrations of P in nonmycorrhizal plants, and reduced leaf concentrations of Ca in both mycorrhizal and nonmycorrhizal plants. Mycorrhizal inoculation increased leaf P, K, Mg and Mn concentrations, but reduced leaf N concentration. Low P regimes reduced final seed yield by diminishing both the number of pods per plant and the number of seeds per pod. Mycorrhizal inoculation significantly enhanced seed yield under low P regimes by increasing seed weight, the number of pods per plant, and the number of seeds per pod.     

Identification of some major cytokinins in Phaseolus vulgaris and their distribution

The determination of the various endogenous cylokinins and their distribution among organs is important in understanding their role in growth and development in the intact plant. Cytokinins in young plants of Phaseolus vulgaris were purified by immunoaffinity chromatography and HPLC, and characterised by UV spectra. Zeatin nucleotide (zeatin riboside-5'-monophosphate) and isopentenyladenine nucleotide (isopentenyladenosne-5'-monopnosphate) were the most abundant cytokinins in all organs. Their identities were confirmed by GC-MS. The levels of zeatin, zeatin riboside, isopentenyladenine and isopentenyladenosine never exceeded 5% of the nucleotides, as assessed by a methodology that preserves cytokinin nucleotides. Three extraction methods were compared with qualitatively similar results, though differing in their suppression of nucleotidase activity. Cytokinin nucleotide levels were greater in the stems and petioles than in the roots and leaves on a per gram fresh weight basis, and were greater in the stems than in the other organs on a per plant basis. Levels of the zeatin and isopentenyladenine nucleotides were about equal in the stems and leaves, but in the petioles the zeatin nucleotide levels were about twice the level of isopentenyladenine nucleotide, while in the roots they were about half the isopentenyladenine nucleotide level. The importance of considering the cytokinin form is emphasised.     

Partial purification of a plasma membrane flavoprotein and NAD(P)H-oxidoreductase activity

Plasma membrane flavins and pterins are considered to mediate important physiological functions such as blue light photoperception and redox activity. Therefore, the presence of flavins and pterins in the plasma membrane of higher plants was studied together with NAD(P)H-dependent redox activities. Plasma membranes were isolated from the apical hooks of etiolated bean seedlings (Phaseolus vulgaris L. cv. Limburgse Vroege) by aqueous two-phase partitioning. Fluorescence spectroscopy revealed the presence of two chromophores. The first showed excitation maxima at 370 and 460 nm and an emission peak at 520 nm and was identified as a flavin. The second chromophore was probably a pterin molecule with excitation peaks at 290 and 350 nm and emission at 440 nm. Both pigments are considered intrinsic to the plasma membrane since they could not be removed by treatment with hypotonic media containing high salt and low detergent concentrations. The flavin concentration was estimated at about 500 pmol mg^?1 protein. However difficulties were encountered in quantifying the pterin concentrations. Protease treatments indicated that the flavins were non-covalently bound to the proteins. Separation of the plasma membrane proteins after solubilisation by octylglucoside, on an ion exchange system (HPLC, Mono Q), resulted in a distinct protein fraction showing flavin and pterin fluorescence and NADH oxidoreductase activity. The flavin of this fraction was identified as flavin mononucleotide (FMN) by HPLC analysis. Other minor peaks of NADH:acceptor reductase activity were resolved on the column. The presence of distinct NAD(P)H oxidases at the plasma membrane was supported by nucleotide specificity and latency studies using intact vesicles. Our work demonstrates the presence of plasma membrane flavins as intrinsic chromophores, that may function in NAD(P)H-oxidoreductase activity and suggests the presence of plasma membrane bound pterins.     

The role of sulphur in detoxication of cadmium in young sugar beet plants

In young sugar beet plants cadmium suppressed the activity of nitrate reductase, glutamine synthetase and glutamate dehydrogenase, whereas sulphur exhibited a protective role towards activity of these enzymes, except of glutamine synthetase. Protein synthesis was suppressed in the absence of S in nutrient medium; the lowest level was at 10^-3 M Cd²⁺. Chloroplast pigment contents were increased by S while Cd²⁺, even in the lowest concentration, (10⁻⁵ M) showed a repressive effect. The highest concentrations of Cd²⁺ (10−3 M) caused a decrease in dry mass, whereas S induced its increase. Nitrate content was increased in the presence of Cd²⁺ and decreased by increased concentration of S. Acknowledgement: The authors acknowledge financial support of the Ministry for Science and Technology of Serbia. The paper was presented at 9th Congress of the Federation of European Societies of Plant Physiology, Brno, Czech Republic, 3–8 July 1994.     

Dominance, competition, and energetic reserves in the European starling, Sturnus vulgaris

We investigated the relationships between social dominance,competition for food, and strategies of body mass and fat regulationin the European starling (Sturnus vulgaris). In birds housedin groups of three, subdominant birds stored more fat than dominants.A removal experiment established a causal link between socialdominance and fat reserves; in groups that had the dominantindividual removed, the remaining birds reduced body mass andfat, relative to control groups that had the subordinate removed.In a second experiment, we investigated the influences of degreeof competition for food and dominance on body mass and fat reserves.Birds under high competition increased fat reserves and tendedto have higher body mass than birds under low competition. Theincrease in fat reserves was higher in the subdominants thanin the dominants. These results are consistent with hypothesesconcerning dominance-dependent access to food; subdominant birds,or birds under increased competition, may store more fat asan insurance against periods when food cannot be obtained. However,relations between dominance, body mass, and fat reserves mayalso arise through other proximate factors relating to dominance-dependentcosts and benefits of fat storage, such as predation risk andenergetic expenditure.     

Free l-amino acids and d-aspartate content in the nervous system of Cephalopoda. A comparative study

We have determined the content of free l-amino acids and d-aspartate in the nervous tissue of three representative cephalopods: Sepia officinalis, Octopus vulgaris, and Loligo vulgaris, and the optic lobes of adult and embryo Sepia officinalis. Taurine is the most abundant amino acid in the cephalopod nervous tissue. Its content amounts to more than 50% of the total free amino acids. The other most concentrated amino acids are Glu, Ala, Asp, and GABA. High concentrations of d-aspartate were found in the nervous tissue of all cephalopods examined (7–12 μmol/g wet tissue) which represents 50–80% of the total aspartate (d + l), depending on the animal. Among the various regions of the brain of Octopus vulgaris, d-aspartate was found to be evenly distributed in the various regions of the brain. In nerve tissue of Sepia officinalis, there is no significant difference in the pattern of free l-amino acids, in particular of the d-aspartate concentration, between adults and embryos, except for GABA, Gly, His and Thr. This suggests that d-aspartate in nerve tissue of the Cephalopoda is of endogenous origin and not a product of accumulation from exogenous sources. From a comparative study of the content of d-aspartate in the nervous tissue of different animals, we found that protostomia contain a significantly higher amount than deuterostomia. Thus, d-aspartate could be a criterion to distinguish the protostomia phyla from the deuterostomia phyla.