Plant Science Letters最新文献

The seed lectins of Phaseolus vulgaris cv. Contender typically consist of five tetrameric isolectins E₄, E₃L, E₂L₂, EL₃ and L₄. However electrophoretic and isoelectric focusing analysis of each purified protomer show a great heterogeneity. We demonstrate that each tetrameric isolectin exists in five different electrophoretic forms depending on the amount of Mn²⁺ cation bound to each isolectin. The effects of Mn²⁺ binding on charge and/or molecular properties of the protomers are discussed. Under the same experimental conditions, if we use Ca²⁺ ions instead of Mn²⁺, the abovemodifications are not observed.

Using the carbon isotope ratio ${}^{13}\text{C}{}^{12}\text{C}$ we have determined the relative importance of carbon flow from the seed reserves and the carbon provided by leaf photosynthetic fixation during the course of development of maize seedlings. The transition from the heterotrophic stage to the autotrophic one corresponds to a growth crisis which occurs on the 10th day in our conditions. During the first 7 days after germination δ ¹³C in leaves and roots is the same as that of the reserve tissues, then a rapid isotropic dilution by incorporation of photosynthetic carbon is observed. The balance between heterotropic and autotrophic carbon is obtained on the 10th day in the leaves but only on the 13th or 14th day in the roots. No autotropic carbon occurs in the roots before the 10th day. It seems that the growth crisis would be due or corresponds, at least partially, to the setting up of translocative function of products from the leaves to the roots.

Four NADP-malate dehydrogenase (NADP-MDH) (EC 1.1.1.82) isozymes from spinach leaves have been purified to apparent homogeneity by DEAE-cellulose and affinity chromatography, and molecular sieving. They have the same native molecular weight (≈57 000) as determined by sedimentation equilibration analysis. They can be distinguished by their eletrocphoretic and chromatographic (over DEAE-cellulose) behaviors. On this basis, they constitute two sets of two enzymes each: MDH-A and -B, and MDH-C and -D. Catalytic properties of the most abundant isozyme, MDH-A, have been studied. Both NADPH and oxaloacetate inhibit the forward reductive reaction. Other kinetic parameters are also presented.

Sodium chloride (salt) tolerant callus was selected from leaf-derived embryogenic callus of Pennisetum purpureum. The tolerant callus was obtained after repeated subculture on medium containing 1.25% NaCl (direct selection), or after gradually increasing salt concentration to 2% during serial subculture (step-wise selection). For both types of callus optimal growth occurred on 0.25% NaCl. Fresh weight to dry weight ratios (FW/DW) decreased in unselected callus grown on high (1.25–2%) salt concentrations, but not in tolerant callus. The callus obtained by direct selection was less sensitive to KCl than unselected callus. After 30–40 weeks under selection, the tolerant callus became necrotic, but healthy callus was recovered from it after transfer to salt-free medium. The callus recovered showed no retention of tolerance and preliminary experiments indicated that plants regenerated from it were more sensitive to salt irrigation than those regenerated from unselected callus.

NADH-nitrate reductase (EC 1.6.6.1) from spinach (Spinacea oleracea L. v. Noorman) has been purified 3400-fold by a multi-stage procedure involving streptomycin sulphate, (NH₄)₂SO₄, hydroxylapatite, molecular seiving and two stages of affinity chromatography using blue-Sepharose and 5′ AMP-Sepharose. The enzyme has a specific activity of 51 μmol NO₂⁻ produced min⁻¹ mg⁻¹ and a functional haem with extinction coefficients (mM) of 127 at 412 nm (oxidized) and 172 at 423 (NADH-reduced). Gel electrophoresis indicates two sub-units of approx. 110 000 and 120 000.

The photodynamic action of the xanthene dye rose bengal upon pea leaf tissue was investigated. Irradiation of pea leaf discs treated with aqueous solutions of the sensitizer resulted in the loss of chlorophyll. Irradiation through a filter of rose bengal solution did not result in chlorophyll loss. The loss of chlorophyll was dependent upon light intensity and oxygen levels. The enchancement of pigment loss in leaf discs supplied with deuterium oxide (D₂O) supports a photodynamic mechanism involving singlet oxygen (¹O₂).

Two isolectins have been isolated from Lathyrus ochrus (L.) DC. seeds by ammonium sulfate precipitation, affinity chromatography on Sephadex G-100 and subsequent chromatofocusing. The isolectins, whose isoelectric points are respectively pH 7.2 and pH 6.0, have a relative molecular mass about 49 000 and are tetramers consisting of two slightly different kinds of light (M_r 4500) and heavy (M_r 20 000) subunits. The amino acid composition, N-terminal amino acids, carbohydrate and metal content of both the isolectins and their subunits have been compared. The isolectins are non-specific in hemagglutination and agglutinate equally well human erythrocytes of different ABO groups. Their hemagglutinating activity is inhibited best by D-mannose, D-glucose and their α-methylglucosides derivatives. They share antigenic determinants in common with other Lathyrus lectins and other lectins belonging to the Vicieae tribe.

Dihydromaleimide (DHMD) and its O-β-glucoside (G-DHMD) are synthesized after germination of pea (Pisum sativum L., cv. Progress No. 9) seed and increase in content accompanying the growth of the shoot. The free aglycone is mostly localized in the apical region, while the glucoside is distributed in the lower par of the shoot. Neither the cotyledons nor the root contain these compounds. The synthesis of DHMD is promoted by phytochrome action but that of the glucoside is not, although the glucoside accumulate more in red light than in darkness. However, the increase of DHMD is not great enough to explain the red light-induced growth inhibition.

Septoria nodorum produced cell wall-degrading enzymes (CWDE) (oolygalacturonase (PG), xylanase (XY) and cellulase (CX)) both in mineral medium supplemented with wheat cell walls and in inoculated wheat leaves. The same in vitro and in vivo isoenzyme pattern for PG (pI 6.2 and 9.4) and XY (pI 5.2) was exhibited by isoelectric focusing resolution. CX was present in culture filtrates with one poorly resolved peak (pI 4.3–4.7). In infected tissues, an additional peak at pI 7.8 appeared. Some characteristics of S. nodorum polysaccharidases were compared with those of other leaf spot pathogens.

In the unicellular green algae, Chlorella fusca and Ankistrodesmus (Monorhaphidium) braunii, nitrate uptake in the light as in the dark was stimulated by physiological concentrations (20 μM) of abscisic acid (ABA), up to 200% by 500 μM. Dark respiration was increased to a similar extent by low ABA concentrations, but up to 13-fold by 500 μM ABA. Addition of 50 mM glucose raised the respiration level to approx. 3-fold, but did not alter the ABA stimulation. Photosynthetic O₂ evolution showed only insignificant inhibition by ABA at high concentrations. The intracellular level of glucose, not that of sucrose, was elevated in the presence of ABA. This suggests that increased starch degradation may be involved in the stimulation of respiration and nitrate metabolism by ABA, rather than direct interference with the plasmalemma. The data show an action of ABA in algae although to our present knowledge, it is not produced in their cells.