The Effects of Photoperiod on Flower-bud Development in Phaseolus vulgaris

For a variety of Phaseolus vulgaris of Peruvian origin, extendingthe daylength from 11 to 15 or 16 h with low-intensity incandescentor natural light, while not affecting the rate of initiationof flower primordia, inhibited the development of the flowerbuds and caused many, and sometimes all of them, to senesceand abscise. The inhibition of the oldest flower bud was firstdetected at the stage of pollen formation. The long photoperiodsalso inhibited the elongation and over-all development of theterminal inflorescence but, in contrast, promoted the elongationof those internodes below the first trifoliate leaf and alsothe elongation of the petioles.     

Development of Cotyledon Cell Structure in Ripening Phaseolus vulgaris Seeds

Changes in weight, nitrogen content, and cell fine structurewere followed in ripening cotyledons of greenhouse-grown beans.The seeds mature within 53–56 days from flowering, cotyledonweight and nitrogen content increasing most rapidly betweendays 22 and 34. The cotyledon parenchyma cells first becomevery highly vacuolate, but soon the large vacuoles are dividedup and converted to reserve protein bodies, while cell expansioncontinues. Vacuole subdivision is accompanied by synthesis ofcytoplasm containing masses of rough-surfaced ER (endoplasmicreticulum), which persists till the cotyledons dry out, andpresumably synthesizes the reserve protein. Starch grains growwithin plastids to reach diameters of 50 µ. Young cotyledonsare green but chlorophyll disappears when the seed dries. Mostorganelles are recognizable in dry cotyledon cells; the ER is,however, replaced by small vesicles. Ribosomes are dispersedfree in the cytoplasm during dehydration; this could indicatea destruction of mRNA (messenger ribonucleic acid) in preparationfor a switch to a different metabolic activity during germination. Some comparisons are drawn between cell fine structure in thecotyledons during ripening and germination.     

Cellular double-stranded RNA in Phaseolus vulgaris

Summary High molecular weight double-stranded (ds) RNAs have been detected in apparently virus-free French (common) bean Phaseolus vulgaris cv. Black Turtle Soup (BTS). Several other bean cultivars were free of detectable high molecular weight dsRNAs. The dsRNAs have been partially characterized and have homology to the BTS genome as well as to the genomes of other bean cultivars. The T_m of hybrids formed between BTS DNA and denatured dsRNA have been estimated.     

Temperature Effects on Mitochondrial Respiration in Phaseolus acutifolius A. Gray and Phaseolus vulgaris L

Electron transport, using succinate as a substrate, was measured polarographically in mitochondria isolated from Phaseolus vulgaris and P. acutifolius plants at 25°C and 32°C. Mitochondria isolated from P. vulgaris plants grown at 32°C had reduced electron transport and were substantially uncoupled. Growth at 32°C had no effect on electron transport or oxidative phosphorylation in P. acutifolius compared to 25°C grown plants. Mitochondria isolated from 25°C grown P. vulgaris plants measured at 42°C were completely uncoupled. Similarly treated P. acutifolius mitochondria remained coupled. The uncoupling of P. vulgaris was due to increased proton permeability of inner mitochondrial membrane. The alternative pathway was more sensitive to heat than the regular cytochrome pathway. At 42°C, no alternative pathway activity was detected. The substantially greater heat tolerance of P. acutifollus compared to P. vulgaris mitochondrial electron transport suggests that mitochondrial sensitivity to elevated temperatures is a major limitation to growth of P. vulgaris at high temperatures and is an important characteristic conveying tolerance in P. acutifolius.     

Endogene Stoffproduktionsrhythmen bei Phaseolus vulgaris

Experimente mit vollausgewachsenen Primär- und Folgeblättern der Buschbohne cv. Saxa unter programmierten Klimabedingungen ergaben bei der Bestimmung der Stoffproduktion mit Hilfe eines Kalorimeters rhythmische Änderungen in dem auf die assimilierende Blattfläche (V_F) bzw. das Trockengewicht bezogenen (V_T) Energiegehalt der produzierten Pflanzenstoffe. Die Trockensubstanzproduktion paßte sich regelmäßig der in der Klimakammer eingestellten Photoperiode an. Am Ende einer Lichtperiode ist der auf die Blattfläche bezogene Kalorienwert V_F stets wesentlich höher als am Ende einer Dunkelperiode; die Pflanze arbeitet also nur im Licht mit positiver Bilanz. Bezieht man den Energiewert jedoch auf das Trockengewicht (V_T), ist es gerade umgekehrt, d. h. in der Dunkelheit werden relativ mehr energiereiche Substanzen angehäuft als im Licht. Im Dauerlicht und Dauerdunkel schwingt der Rhythmus nach. Beim Umschalten auf eine veränderte Photoperiode paßt sich der Rhythmus erst nach Durchlaufen je einer Licht- und Dunkelphase der neuen Behandlung an. Als Auslöser scheint ein einmaliger Hell- und Dunkelwechsel möglich, verschiedene Lichtqualitäten und Photoperioden bleiben ohne Einfluß. Der Zeitgeber für die endogene Rhythmik ist noch unbekannt     

Control of Thylakoid Growth in Phaseolus vulgaris

An attempt was made to answer whether the extent of thylakoid growth in Phaseolus vulgaris is controlled by a feedback inhibition mechanism, operating after insertion of all of the necessary components of the mature thylakoid, in the right amounts and ratio, or by parameters independent of the developmental stage of the membrane. This was done by following the growth of thylakoids, as monitored by the rate of chlorophyll accumulation and the rate of thylakoid protein synthesis, in etiolated plants exposed either directly to continuous light (transformation of prolamellar body to mature thylakoid) or first to periodic light and then to continuous light (transformation of prolamellar body to primary thylakoids and then to mature thylakoids). It was found that prolonged etiolation has no effect on the rate of thylakoid synthesis in continuous light. However, prolonged preexposure to periodic light diminishes drastically the rate of new thylakoid synthesis in continuous light. Since the thylakoids formed in the latter case are far from being complete, it seems that thylakoid growth can stop long before all of the necessary components are incorporated. Parameters independent of the developmental stage and composition of the membrane, therefore, seem to control membrane growth.     

The Ultrastructure of Phaseolus vulgaris Chloroplasts

A comparison of bean chloroplasts after being fixed in potassiumpermanganate, osmium, and formaldehyde coupled with negativestaining shows that the general organization of the chloroplastis similar in all cases. However, the mature chloroplasts ofbean vary considerably in the extent and orientation of theinternal membranes—the grana and the interconnecting membranesbetween the grana. The interconnecting membranes are thin, branching,flexuous structures. This is illustrated by serial sectionsand by cross- and face-view sections of osmium- fixed chloroplastsand the best model, which allows for a considerable flexibilityin the orientation of the grana and also describes the thininterconnecting membranes between the grana, is the grana-fretworksystem proposed by Weier (1961). Furthermore, the comparative studies show that the internalregions of grana are separated from the stroma and that thegrana-fretwork systems appear to be a continuous membrane system.This membrane is single along the frets, end compartments, andgranal margins. It is double in the partitions of the granabut separated by a component, possibly a cementing material,which does not stain. It is suggested that this membrane isstructurally similar in the chloroplasts of higher plants, butthat its overall organization may vary from one plant to another.     

Spectroscopic characterization of Phaseolus vulgaris leucoagglutinin

Phaseolus vulgaris leucoagglutinin is a homotetrameric legume lectin possessing the canonical dimeric structure common to other legume lectins. In order to gain insight into the stability of the protein in an acidic environment, it was characterized by CD and fluorescence studies at pH 2.5. This was then compared with the native protein at physiological pH (7.2). The extinction coefficient of the native protein was calculated to be 3.58x10(4) from its UV absorption spectra. The far- and near-UV CD spectra of the protein at pH 2.5 showed very little difference even though the protein was found to exist as a dimer at pH 2.5. The fluorescence emission maxima of the protein upon excitation at 280 nm were found to shift only from 331 nm at pH 7.2 to 333 nm at pH 2.5. Based on the above observation it was concluded that the protein exhibits extreme pH stability especially in the acidic range. The secondary and tertiary structure of the protein is lost only when it is incubated for two days in 6 M GdnHCl at pH 2.5. At pH 7.2 it could be denatured in 6 M GdnHCl after one week of incubation.     

Monosomics in common bean,Phaseolus vulgaris

Summary Two monosomics of Phaseolus vulgaris (2n = 22) were found among selfed progeny of plants treated with colchicine. The monosomic chromosomes involved were identified as chromosomes H and J according to the previously suggested Giemsa karyotype. Both monosomic plants had slower growth rate and smaller size as compared with their respective euploid sibs. However, no apparent morphological characteristics distinguished the two monosomics. The frequencies of transmission through selfing of monosomics H and J were 9% and 10 % respectively.     

Apical Dominance in Phaseolus vulgaris L.

Although determinations of the ABA content of lateral buds ofPhaseolus vulgaris revealed no difference between decapitatedand intact control plants in the first 12 h following decapitation,a relative decrease in the ABA content of lateral buds of decapitatedplants was detectable 24 h following decapitation. Shoot decapitationwas also observed to result in a decrease in the ABA contentof stem tissue. The application of IAA to the stem of decapitatedplants prevented these changes and increased the ABA contentof stem tissue relative to that of intact plants. The levelsof IAA and ABA were also determined in the stem tissue fromthe nodes of intact bean plants. The possible interdependenceof these two plant hormones was further investigated by a studyof [2_–14ClABA metabolism. The results are discussed inrelation to the possible role of these hormones in apical dominance. Key words: Apical dominance, Abscisic acid, Indole-3-acetic acid     

Phaseollin formation and metabolism in Phaseolus vulgaris

Following fungal-inoculation, P. vulgaris was found to produce small amounts of 7,4′-dihydroxyisoflavone (daidzein), 7,2′,4′-trihydroxyisoflavone, 7,2′,4′-trihydroxyisoflavanone, (6aR, 11aR)-3,9-dihydroxypterocarpan, and (3R)-7,2′,4′-trihydroxyisoflavan. The structures of the latter four compounds were confirmed by synthesis. The principal pterocarpans isolated were phaseollidin and phaseollin and ORD spectra indicate that these compounds have the same (6aR, 11aR)-configuration as 3,9-dihydroxypterocarpan. A pathway leading to phaseollidin and phaseollin is proposed involving 2′-hydroxylation of daidzein, reduction to the isoflavanone, further reduction, dehydration and cyclization to the pterocarpan, and prenylation to give phaseollidin and then cyclization and dehydrogenation to give phaseollin. No evidence of prenylation at the isoflavone or isoflavanone stage was obtained. The phaseollin metabolite, (6aS, 11aS)-6a-hydroxyphaseollin, was also detected.     

Cytokinin metabolism in Phaseolus vulgaris L.

The major cytokinins in stems of decapitated, disbudded bean plants have been identified by enzymic degradation, Sephadex LH20 and reversed phase high performance liquid chromatography, and by combined gas chromatography-mass spectrometry as 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9--D-ribofuranosylpurine (zeatin riboside), 6-(4-hydroxy-3-methylbutylamino)-9--D-ribofuranosylpurine (dihydrozeatin riboside), and the 5-phosphates of these compounds (zeatin ribotide and dihydrozeatin ribotide). Minor cytokinins in this tissue were tentatively identified as dihydrozeatin-O--D-glucoside and zeatin ribotide-O--D-glucoside. [8-¹⁴C-]Dihydrozeatin appeared to be rapidly metabolized to dihydrozeatin ribotide when supplied to segments of stems from decapitated plants. These results are discussed in relation to the metabolism and distribution of cytokinins in the whole plant.Abbreviations TEAB triethyl ammonium bicarbonate - UV ultra-violet - GCMS gas chromatography-mass spectrometry - HPLC high performance liquid chromatography - TMS trimethyl silyl     

Methylammonium Transport in Phaseolus vulgaris Leaf Slices

Methylammonium (as a nonmetabolized analog of ammonium) transport was studied in leaf slices of Phaseolus vulgaris L. var. `Hawkesbury Wonder.' The relationship of influx to external pH (6.0-10.5) shows that the influx at low external pH is a larger fraction of that at high external pH than would be expected from the pK_α of methylammonium and the assumption that only CH₃NH₂ is entering the cells. The relationship between methylammonium influx and external methylammonium concentration shows some evidence of saturation; this is a function of the transport system rather than of the (limited) methylammonium metabolism in the cells. The “equilibrium” concentration ratio for methylammonium between leaf slices and bathing medium is far higher than can be explained by the transport of CH₃NH₂ alone and the pH of the compartments involved. These three lines of evidence strongly suggest that there is an influx of CH₃NH₃⁺, possibly by a uniporter driven by the electrical potential of the cytoplasm with respect to the medium, as has been shown for other plant cells. Competitive inhibition of methylammonium influx by ammonium suggests that there is also an ammonium transport system. The significance of this for the recycling of N within the plant and for exchange of gaseous NH₃ between leaves and the atmosphere is discussed.