绿豆下胚轴中的雌二醇结合位点

越来越多的证据表明,动物的甾类激素广泛存在于植物体内(Hewitt等1980,周永春和曹宗巽1982,王焕民和曹宗巽1986,Jones和Roddick 1988,Simons和Grinwich 1989,Zhang等1991a,b)。而这些激素对植物的生长发育也具有多方面的作用,如雌二醇可以促进多种植物开花,增加菠菜、女蒌菜等雌花比例;雌酮和雌二醇在适当浓度下可以促进豌豆     

Uptake of Iodide by Excised Bean Roots

Mesophyll cells of leaf slices of bean (Phaseolus vulgaris L.) absorb six to ten times more K⁺ than Rb⁺ from 0.1 mM single chlorides of these cations. Absorption of ⁴²K⁺ from 0.1 mM⁴²KCl is much more inhibited by low concentrations of Rb₂SO₄ than by K₂SO₄. The isotherm for K⁺ absorption is biphasic in the range 0.1–1.1 mM, and K⁺ is more effective than Rb⁺ in causing transition from phase 1 to phase 2.     

Phytochrome-induced Increase of Fluorescein Translocation in Mung Bean Hypocotyls

Moderate doses of red (660 nanometer) irradiation cause a rapid increase in the translocation of fluorescein in dark-grown mung bean hypocotyl (Vigna radiata L.) segments. The increase fails to appear following large doses of red (660 nanometers) irradiation. The red induced increase is prevented by a subsequent far red (730 nanometer) irradiation. Reversibility suggests the participation of phytochrome in the process. The increase in translocation is attributed to the generation of a positive electrostatic charge in the plasma membrane by some action of phytochrome on membrane molecules.     

Ion Transport in Isolated Protoplasts from Tobacco Suspension Cells: II. Selectivity and Kinetics

Protoplasts were enzymically isolated from suspension cultured cells of Nicotiana glutinosa L. and aspects of transport selectivity and kinetics were studied. In the presence of Ca²⁺, transport was selective for K⁺ (⁸⁶Rb) over Na⁺. ³⁶Cl⁻ transport was inhibited by Br⁻ or I⁻ but not by H₂PO₄⁻. The kinetic data for short term (30 minutes) K⁺ influx over the range of 0.05 to 100 millimolar KCl were complex but similar to those observed in other plant tissues. In contrast, the kinetic data for Cl⁻ and H₂³²PO₄⁻ over the same concentration range were different from those observed for K⁺, and could be accounted for by a single isotherm in the range of 0.05 to 4 millimolar and by an almost linear increase in influx rate above 4 millimolar. The kinetic data for Cl⁻ transport into intact cultured cells were identical in character to those observed for isolated protoplasts. The results support the view that enzymic removal of the cell wall produced no significant alteration in the transport properties of the protoplast.     

Ion Selectivity and Competition in Channelrhodopsins

Channelrhodopsins are light-gated ion channels of green algae. They are widely used for the analysis of neuronal networks using light in the emerging field of optogenetics. Under steady-state light conditions, the two open states, O1 and O2, mediate the photocurrents with different ion conductance and selectivity. To understand the conducting process as well as its optogenetic applications, it is important to study ion binding and transport of this promiscuous cation channel. Here, we present an enzyme kinetic algorithm that allowed us to calculate the ion composition of the initial and steady-state photocurrents for multication media. The approach is based on current-voltage relations determined for the individual ions H⁺, Na⁺, Ca²⁺, and Mg²⁺. We identify and quantify the widely different competition of the ions in wild-type channelrhodopsin-2 and two high-performing channelrhodopsin variants CatCh+ and C1V1. Both variants show enhanced Ca²⁺ conductance, but only CatCh+ displays high steady-state Ca²⁺ currents at neutral pH due to reduced H+ competition and low inactivation. We demonstrate that for optogenetic applications, one should always take into account that the variable equilibria of the two open states depend on light intensity, voltage, and the ionic composition of the medium.     

Cooperative Substrate Oxidation by Mitochondria from Castor Bean Hypocotyls

Cooperative oxidation of succinate and exogenous NADH was followed in the mitochondria from five- to six-day-old castor bean (Ricinus communisL.) seedlings. Although succinate was oxidized at a much higher rate than NADH, the former inconsiderably (less than 15%) inhibited the oxidation of the latter substrate in state 4, while, in state 3 (in the presence of ATP), the two substrates did not compete and were jointly oxidized. When two substrates were oxidized by the mitochondria with the alternative CN-resistant oxidase (AO) inhibited with salicylhydroxamic acid, the rate of NADH oxidation in state 4 dropped by over 40% as compared to the initial rate. Meanwhile, the rate of succinate oxidation was not considerably affected by AO inhibition. We believe that one of the AO functions in the mitochondria is to provide for noncompeting oxidation of two (or more) substrates by employing two (or several) dehydrogenases of the respiratory chain.     

Effect of Different Cytokinins on Ethylene Production by Mung Bean Hypocotyls in the Presence of Indole-3-Acetic Acid or Calcium Ion

Kinetin has been shown to act synergistically with indole-3-acetic acid (IAA) or calcium ion (Ca²⁺) to stimulate ethylene production. Several commercially available cytokinins (kinetin, kinetin-riboside, benzyladenine, benzyladenine-riboside, isopentenyladenine, isopentenyladenine-riboside, and zeatin) as well as noncytokinin bases (adenine and xanthine) were administered to mung bean (Phaseolus aureus Roxb.) hypocotyls to study their effects, alone or in combination with IAA or Ca²⁺, on ethylene production. In the presence of IAA or Ca²⁺, all cytokinins tested synergistically stimulated ethylene production and were as effective or nearly as effective as kinetin. Noncytokinin bases (adenine and xanthine) were, however, inactive in this system.     

Development of Vacuolar Membranes during Elongation of Cells in Mung Bean Hypocotyls

The development of vacuolar membrane in the elongating hypocotylsof the mung bean was investigated. The hypocotyls from 3-day-oldseedlings were dissected into the dividing, elongating and matureregions. The diameter of protoplasts prepared from the matureregions was about 3-fold greater than the diameter of thosefrom the dividing region. The activity of inorganic pyrophosphatase,an enzyme associated with the vacuolar membrane, was detectableeven in the dividing region. The level of pyrophosphatase wasquantified by slot-blot analysis with the pyrophosphatase-specificantibody. The relative amount of pyrophosphatase per cell, calculatedon the basis of DNA content, increased about 4-fold during cellmaturation. When the densities of vacuolar membranes were comparedby sucrose density gradient centrifugation, there was no markeddifference among the preparations from three regions. Furthermore,most of the major proteins were common to the three purifiedpreparations of vacuolar membranes. From the results, it appearsthat most components of vacuolar membrane may be synthesizedde novo and added to the existing membrane during cell elongation.Furthermore, it is proposed that the H⁺-pyrophosphatase mayactively hydrolyze its substrate to maintain the internal acidityof expanding vacuoles, because pyrophosphate was present ata concentration of more than 70 µM in the dividing andelongating regions. (Received August 7, 1989; Accepted January 11, 1990)     

Partial Purification of a Soluble Gibberellin-Binding Protein from Mung Bean Hypocotyls

A soluble binding protein specific for GA₄, GA₇ and GA₉ waspartially purified from mung bean hypocotyls, and its characteristicswere examined. Affinity chromatography using immobilized GA₃coupled to Sepharose 4B via the C-7 carboxyl group was veryeffective for purification of the protein. The molecular weightof the protein in its native state was estimated to be 150–200kDa by gel-permeation chromatography. This protein may be aheterooligomer consisting of two subunits (23 kDa and 35 kDa).The optimum pH for binding of GA₄ to the protein was around6.0 and the apparent dissociation constant (K_d) was 310^-7 M. (Received April 24, 1992; Accepted December 16, 1992)     

Inhibition of Ion Transport in Excised Barley Roots by Abscisic Acid; Relation to Water Permeability of the Roots

Previous papers have shown that abscisic acid can inhibit transportof ions across the root to the xylem vessels, resulting in reducedexudation from excised roots or inhibiting guttation from intactplants. However, it has not been established whether the inhibitionwas due to a reduction in salt transport (J_s) or in permeabilityof the roots to water (L_p). This paper investigates the effectof ABA on L_p and J_s separately. It is shown that L_p increasedin ABA and then fell, but was about the same as in control rootswhen transport was inhibited. The effect of ABA on exudationtherefore appeared to be mainly due to reduction in J_s. Inhibitionof J_s was also present in intact, transpiring plants and sowas not due to reduced water flow. The inhibition of ion releaseto the xylem affected Na⁺, Mg²⁺, Ca²⁺, and phosphate as wellas the major ion in the exudate, K⁺. It is concluded that ABAinhibits salt transport to the shoot by acting on ion transportinto the xylem, and not by reducing water flow coupled withsalt transport.     

Characterization of Proteins of Nuclear Envelopes Prepared from Mung Bean Hypocotyls

The polypeptide composition of nuclear envelopes prepared fromhypocotyls of mung bean (Vigna radiata) was investigated. Thetissue was homogenized in the presence of Triton X-100 and nucleiwere isolated by differential and discontinuous Percoll gradientcentrifugation. The nuclei were subjected to sonication in 2M KC1 or 50 mM lithium diiodosalicylate and then the nuclearenvelopes were collected by centrifugation. Proteins in theenvelope fraction were analyzed by sodium dodecylsulfate-polyacrylamidegel electrophoresis and blotting techniques. When the envelopefraction was incubated with [-³²P]ATP, 10 to 15 polypeptideswere labeled and the intensity of labeling of some of thesepolypeptides was enhanced by the addition of calcium ions. Theresults suggest the presence of a protein-phosphorylation systemin nuclear envelopes. Three polypeptides of 100, 42, and 40kDa stained blue with the cationic carbocyanine dye "Stains-all",and they were labeled with ⁴⁵Ca²⁺ on a transfer membrane. Thelectin concanavalin A recognized glycoproteins that migratedas polypeptides of 50, 49, 47, 43, 35 and 32 kDa, respectively.Of these polypeptides the two larger ones were prominent andwere solubilized by treatment of the envelope fraction withKCl at 2 M but not at less than 100 mM. These results suggestthat the mung bean nuclear envelope contains some calcium-bindingproteins and glycoproteins. These newly identified proteinsmay become useful as characteristic markers of the nuclear envelope. (Received July 16, 1993; Accepted December 15, 1993)     

Ion Diffusion Selectivity in Lecithin-Water Lamellar Phases

The diffusion coefficients of Na⁺, Rb⁺, and cl^- were determined in lecithin-water lamellar phases at 18°C as a function of phase hydration. Diffusion was measured within the phase with no transfer between phase and bulk aqueous medium. The relative diffusion coefficients of anion and cation depended strongly on phase hydration. At low water content, the diffusion coefficient of Cl^- was greater than that of Na⁺ or Rb⁺ whereas at high water content both cations diffused faster than the anion. The change in relative diffusion coefficient occurred at 0.24 g water/g phase (24% water). The possibility that a change in conformation of the lecithin polar head occurs at a phase water content of 24% is considered. The diffusion coefficients of all three ions decreased at the water content where the relative diffusion rates inverted. Freeze fracture and polarizing microscopy studies were carried out to obtain information on phase structure. The latter study indicated that a change in long-range organization of the phase occured at 24% water. This change accounts for the decrease in the ion diffusion coefficients at this water content. The change in conformation of the choline phosphate group proposed as an explanation for the change in ion selectivity could lead to changes in long-range organization of the phase as a second order-effect.     

Kinetin-promoted Polyribosome formation in relation to RNA Synthesis in Excised Mung Bean Cotyledons

The relative levels of polyribosomes and total ribosomal materials, the rates of RNA synthesis and the contents of each RNA component were investigated in excised cotyledons of mung bean (Phaseolus radiatus L.) incubated with and without kinetin. 12 h incubation with 50 μmol/ L kinetin markedly increased the levels of polyribosomes and decreased the levels of monoribosome, especially of the ribosomal subunits. In addition, levels of total ribosomal materials (ribosomal subunit+monoribosome+polyribosome) were also increased in cotyledons incubated with kinetin. The kinetin-promoted polyribosome formation could be arrested by the RNA synthesis inhibitor-actinomycin D(ACTD). Kinetin incubation greatly enhanced RNA synthesis and increased that RNA conten. A marked increase was found in the amount of poly(A)+-mRNA, while the levels of other RNA components (25S, 18S rRNA, 4–5S RNA) were also increased to different extent. These results suggest that the promotion of polyribosome formation by kinetin depends upon the de novo synthesis of mRNAs, and the promotion of ribosome con, struction by kinetin may also be related to the synthesis of rRNAs.