Opposing Effects of Aluminum on Inward-Rectifier Potassium Currents in BeanRoot-Tip Protoplasts

Inward currents in root cap protoplasts of the aluminum-tolerant cultivar, Dade, of Phaseolus vulgaris L. were investigated using the whole-cell patch-clamp technique. The properties of these currents were similar to those seen in inward rectifying K⁺ channels in other plant tissues. Replacing bath K⁺ with Na⁺ nearly abolished the observed currents. Higher bath K⁺ concentrations increased inward currents. AlCl₃ in pH 4.7 bath solutions caused inward K⁺ currents to activate more rapidly and at more positive voltages when compared with AlCl₃ free solutions. In 10 μM AlCl₃ the activated inward K⁺ currents were significantly larger than in the AlCl₃-free solution at all voltages except at the most negative voltage of −174 mV and the least negative of −74 mV. In contrast, in 80 μM Al³⁺, when hyperpolarizing voltages were most negative, the inward K⁺ currents were inhibited relative to the currents in 10 μM AlCl₃. Enhancement of inward K⁺ currents by AlCl₃ is consistent with Al³⁺ binding to the external surface of the root cap protoplast, decreasing the surface charge, thus causing the channels to sense a more negative membrane potential. Inhibition of inward K⁺ currents with higher AlCl₃ concentrations and more negative voltages is consistent with Al³⁺ block of K⁺ channels.This revised version was published online in August 2005 with a corrected cover date.     

Secondary mould metabolites of Cladosporium tenuissimum, a hyperparasite of rust fungi

Investigation of the extracts of a culture of Cladosporium tenuissimum, a known hyperparasite of several rust fungi, gave rise to the isolation of cladosporols B-E (2-5). Their structure and stereochemistry were elucidated on the basis of 1H and 13C NMR evidence and CD measures. Cladosporols 1-5 were active in inhibiting the urediniospore germination of the bean rust agent Uromyces appendiculatus.     

Morphological and physiological responses of bean plants to supplemental UV radiation in a Mediterranean climate

During the last few decades many experiments have been performed to evaluate the responses of plants to enhanced solar UV-B radiation (280–320 nm) that may occur because of stratospheric ozone depletion; most of them were performed in controlled environment conditions where plants were exposed to low photosynthetically active radiation (PAR) levels and high UV-B irradiance. Since environmental radiative regimes can play a role in the response of plants to UV-B enhancement, it appears doubtful whether it is valid to extrapolate the results from these experiments to plants grown in natural conditions. The objective of this work was to evaluate the effects on physiology and morphology of a bean (Phaseolus vulgaris L.) cultivar Nano Bobis, exposed to supplemental UV radiation in the open-air. UV-B radiation was supplied by fluorescent lamps to simulate a 20% stratospheric ozone reduction. Three groups of plants were grown: control (no supplemental UV), UV-A treatment (supplementation in the UV-A band) and UV-B treatment (supplemental UV-B and UV-A radiation). Each group was replicated three times. After 33 days of treatment plants grown under UV-B treatment had lower biomass, leaf area and reduced leaf elongation compared to UV-A treatment. No significant differences were detected in photosynthetic parameters, photosynthetic pigments and UV-B absorbing compounds among the three groups of plants. However, plants exposed to UV-A treatment showed a sort of 'stimulation' of their growth when compared to the control. The results of this experiment showed that plants may be sensitive to UV-A radiation, thus it is difficult to evaluate the specific effects of UV-B (280–320 nm) radiation from fluorescent lamps and it is important to choose the appropriate control. Environmental conditions strongly affect plant response to UV radiation so further field studies are necessary to assess the interaction between UV-B exposure and meteorological variability.     

Jasmonates promote abscission in bean petiole expiants: Its relationship to the metabolism of cell wall polysaccharides and cellulase activity

Jasmonic acid (JA) and its methyl ester (JA-Me) promoted the abscission of bean petiole expiants in the dark and light, and the activity of these compounds was almost same. JA and JA-Me did not enhance ethylene production in bean petiole expiants in the light, indicating that the abscission-promoting effects of these compounds are not the result of ethylene. Cells in the petiole adjacent to the abscission zone expanded during abscission but not in the pulvinus, and JA-Me promoted cell expansion in the petiole and the pulvinus. JA-Me had no effect on the total amounts of pectic and hemicellulosic polysaccharides in 2-mm segments of the abscission region, which included 1 mm of pulvinus and 1 mm of petiole from the abscission zone. On the other hand, the total amounts of cellulosic polysaccharides in this region were reduced significantly by the addition of JA-Me in the light. JA-Me had no effect on the neutral sugar composition of hemicellulosic polysaccharides during abscission. The decrease in the endogenous levels of UDP-sugars in the petiole adjacent to the abscission zone was accelerated during abscission by the addition of JA-Me in the light. Cellulase activities of pulvinus and petiole in 10-day-old seedlings were enhanced by the addition of JA. These results suggest that the promoting effect of JA or JA-Me on the abscission of bean petiole explants is due to the change of sugar metabolism in the abscission zone, in which the increase in cellulase activity involves the degradation of cell wall polysaccharides. Jasmonic acid (JA) and its methyl ester (JA-Me) are considered to be putative plant hormones for a number of reasons, including their wide occurrence in the plant kingdom, biologic, activities in multiple aspects at low concentrations, and their interaction with other plant hormones (for reviews see Parthier 1991, Hamberg and Gardner 1992, Sembdner and Parthier 1993, Ueda et al. 1994a). We have already reported that JA and JA-Me and C₁₈-unsaturated fatty acids, which are considered to be the substrates of the biosynthesis of jasmonates, are powerful senescence-promoting substances (Ueda et al. 1982b, 1991a). Senescence symptoms induced by these compounds are identical to those of natural senescence. Recently we have also found that JA inhibited indole-3-acetic acid (IAA)-induced elongation of oat (Avena sativa L. cv. Victory) coleoptile segments by inhibiting the synthesis of cell wall polysaccharides (Ueda et al. 1994b, 1995). These facts led us to study the mode of actions of JA and JA-Me on promoting abscission, which is considered the last dramatic phenomenon of senescence. In this paper we report that JA and JA-Me promote abscission in bean (Phaseolus vulgaris L. cv. Masterpiece) petiole expiants and that the changes in the metabolism of cell wall polysaccharides in the petiole and the pulvinus adjacent to the abscission zone are involved in the promotive effects of these compounds.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - DCB 2,6-dichlorobenzonitrile - HPLC high performance liquid chromatography - IAA indole-3-acetic acid - JA jasmonic acid - JA-Me methyl jasmonate - MES 2-(N-morpholino)ethane-sulfonic acid, monohydrate - TCA trichloroacetic acid - Tris 2-amino-2-hydroxymethy-1,3-propanediole     

Identification and characterization of a nitrate reductase gene from bean (Phaseolus vulgaris) containing four introns

A structural gene encoding nitrate reductase (NR) in bean ( Phaseolus vulgaris ) has been cloned and sequenced. The NR gene encodes a protein of 890 amino acids with a molecular mass of 100 kDa. Comparison to the other known NR gene from bean reveals 76% amino acid identity and comparison to NRs from other species shows amino acid identities ranging from 67 to 77%. At three positions the amino acid sequence displays differences from residues conserved in all other known NR proteins. The coding sequence is interrupted by four introns. Three of them are located at conserved positions in the region encoding the molybdenum cofactor-binding domain. The fourth intron is located in the hinge region between the heme and the FAD domain. This is the only example in which more than three introns have been found in a higher plant NR gene. The mRNA cap site was identified as an adenosine 79 nucleotides (nt) upstream of the ATG translation start codon. Northern analysis shows that the gene is nitrate inducible and highly expressed in trifoliolate leaves of 20-day-old bean plants and only weakly expressed in roots. The gene is also induced by light and sucrose in leaves of dark-adapted plants. The mRNA displays diurnal oscillation under the control of a circadian rhythm. Putative conserved GATA motifs in the promoter are discussed.     

Inheritance of partial resistance to bean rust in the common bean (Phaseolus vulgaris L.)

The inheritance of partial resistance within eight bean cultivars to a single-pustule isolate of bean rust was studied by means of a F₁ diallel test. General combining ability (GCA) and specific combining ability (SCA) were very highly significant over two seasons and in interaction with seasons. The partitioning of the sums of squares indicated the greater importance of GCA in the inheritance of the resistance. Reciprocal effects were not significant. The estimates of narrow-sense heritability in the two seasons were 0.899 ± 0.056 and 0.603 ± 0.065.     

Studies on interspecies competition between the azuki bean weevil,Callosobruchus chinensis,and the southern cowpea weevil,C. maculatus II. Competition under different environmental conditions

The experimental studies was done on the interspecies competition between the azuki bean weevil, Callosobruchus chinensis, and the southern cowpea weevil, C. maculatus, under the different environmental conditions.

1. At 30°C, 70% R. H., the change of food replenishment interval had no influence upon the competition results, and the competition always ended in the extinction of C. maculatus. But there was a tendency for the period of co-existence to be elongated as the interval of replenishment lengthened.
2. At 30°C, 70% R. H., there were no differences in the competition processes and results between the competition using the dry bean (water content about 11%) or the normal one (about 15%).
3. At 32°C, 64% R. H., the competition result was reversed from that at 30°C, 70% R. H. This is thought to be due to the differences of the developmental rates and the numbers of eggs oviposited between the two species at these conditions.
4. In some cases the competition result could be understood from the point of the phenomena of single species populations of both species, but in other cases, the results were in conflict with the expectation from those phenomena. To analyze the competition mechanism, it is necessary to investigate the interaction between species.

     

Preparation of a homogeneous coated vesicle fraction from bean leaves

Summary Using a procedure previously developed for suspension-cultured carrot cells, we have been able to isolate two different coated vesicle-containing fractions from green bean leaves (Vicia faba). The two fractions differ in their isopycnic densities in D₂O-Ficoll as well as in their diameters. One of the fractions (the less dense of the two) is almost 100% pure as judged by negative staining. Because of this the polypeptide pattern obtained from SDS-PAGE is most clear and has enabled a clear recognition of clathrin light chains, in addition to the 190 kDa heavy chain coat component. Significantly the 100k Da and 50k Da polypeptides typical of brain coated vesicles are absent from bean leaf coated vesicles. Due to a) the high degree of vacuolation b) the presence of large amounts of ribulose bisphosphate carboxylase in the postmicrosomal supernatant, the yield of coated vesicles from bean leaves, as compared to nongreen plant cells, or to bovine brain tissue is extremely low (1 mg coated vesicles from 2.4 kg leaf tissue).Abbreviations D₂O deuterium oxide - EGTA ethylene glycol-bis ( amino ethyl ether) N,N,N,N tetraacetic acid - MES, 2 (N-morpholino)-ethanesulfonic acid - PMSF phenyl methylsulfonyl fluoride - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - TRIS Tris-hydroxy methyl amino methane     

Studies on chloroplast division in young leaf tissues of some higher plants

Summary The process of chloroplast division in young leaves of four species (bean, spinach, wheat, and maize) was investigated by light and electron microscopy. Two types of division, i.e., by fission, and by partition were observed.Chloroplast division by fission prevailed in the plant species examined, as shown by the relative abundance of dumbbell-shaped plastids, the characteristic stage in this type of division. Electron dense material, most commonly in the shape of a ring structure in the isthmus of the dividing plastid, was nearly always present in wheat and maize. Similar, but less distinct structures were usually observed in the neck region of constricted bean and spinach chloroplasts.Chloroplast division by partition was found in young leaf tissues of bean and spinach, but was not observed in wheat and maize. The main indication of this type of division is a centripetal invagination of the inner limiting membrane of the plastid envelope which progressively divides the chloroplast stroma into two, nearly equal, parts. Specific membraneous structures resembling myelin figures were usually found close to a dividing chloroplast and may participate in chloroplastokinesis.     

Developmental changes in the inner epidermis of the bean seed coat

Summary The inner epidermis of the bean seed coat shows remarkable structural changes during seed development. At the globular stage of development, a moderately electron-dense substance begins to accumulate in the outer tangential and radial walls of the cells. The staining and fluorescence characteristics, together with the localization of peroxidase in the wall, suggest that this electron-dense material is a phenolic substance. At the same stage of embryo development, structural specialization can be detected in the cytoplasm of the epidermal cells with an increase in the abundance of organelles, especially the endoplasmic reticulum, mitochondria, and dictyosomes. These structural features are similar to those in the underlying branched parenchyma cells. As the seed rapidly expands during the maturation stage of embryo development, the epidermal cells and the inner layers of the branched parenchyma cells begin to degenerate. Small ruptures can be detected in the epidermis, exposing the branched parenchyma cells. These structural changes are discussed in relation to their possible functions during embryo development.