Plant Growth Inhibition and Membrane Penetration by a Homologous Series of Dichlorobenzoate Esters

The homologous series of n-alkyl esters (C₁–C₁₀) of 3,4-dichlorobenzoic acid was synthesized and their effects in inhibiting the growth of Nicotiana meristems were studied. The inhibition of growth was considered in terms of penetration of chemicals into the plant tissue and subsequent cell membrane disruption. Penetration was investigated by applying the emulsified ester to the meristem and then measuring the compound recovered with the isolated surface lipids. Decreasing amounts of 3,4-dichlorobenzoate esters penetrated into the plant as the alkyl chain length of the ester moeity was increased. Essentially no penetration occurred with the n-C₇ through C₁₀ esters tested. The effect of the ester homologues on cell membranes was studied by measuring the efflux of betacyanin from beet root cells. Decreasing amounts of pigments were released as the alkyl chain length of the ester was increased. Minimal cell membrane disruption was found for the C₇–C₁₀ esters. Inhibition of the plant meristem may result from the more rapid penetration of the short chain ester homologues into the plant.     

B-Nine Reversal of Benzimidazole-or IAA-induced Inhibition of Growth and Yield of Cowpea Plants

Growth, flowering, and yield of Cowpea (Vigna catjang) wereinhibited by Benzimidazole (10^-3M) or IAA (10^-2M). These growthinhibitions were reversed by B-Nine (2x10^-3M) which alone waswithout any effect. In combination, IAA and Benzimidazole weremutually antagonistic. A common mechanism is suggested for theB-Nine reversal of the Benzimidazole or IAA inhibition of growth.     

Growth Inhibition by D-Mannosamine and Its Reversal by Glucose and Mannose in Bacillus subtilis

Growth of the Bacillus subtilis wild type strain was severelyinhibited by mannosamine. This inhibitory effect was reversedby the addition of glucose or mannose. Growth in peptone mediumwas accompanied by the consumption of the added glucose andby the accumulation of acetoin. Glucose utilization and acetoinproduction were markedly repressed in the cells grown in thepresence of mannosamine. Growth in the presence of mannosaminewas accompanied by a relative decrease in a protein with themolecular weight of 70,000 as revealed by SDS polyacrylamidegel electrophoresis. Our results indicate that mannosamine'sinhibition of growth is due primarily to low glucose utilizationalthough other cellular metabolic activity also may be involved. (Received August 15, 1983; Accepted April 2, 1984)     

Inhibition of Cation Channels in Human Erythrocytes by Spermine

In erythrocytes, spermine concentration decreases gradually with age, which is paralleled by increases of cytosolic Ca2+ concentration, with subsequent cell shrinkage and cell membrane scrambling. Cytosolic Ca2+ was estimated from fluo-3 fluorescence, cell volume from forward scatter, cell membrane scrambling from annexin V binding and cation channel activity with whole-cell patch-clamp in human erythrocytes. Extracellular spermine exerted a dual effect on erythrocyte survival. At 200 μM spermine blunted the increase of intracellular Ca2+, cell shrinkage and annexin V binding following 48 h exposure of cells at +37 °C. In contrast, short exposure (10-30 min) of cells to 2 mM spermine was accompanied by increased cytosolic Ca2+ and annexin binding. Intracellular addition of spermine at subphysiological concentration (0.2 μM) significantly decreased the conductance of monovalent cations (Na+, K+, NMDG+) and of Ca2+. Moreover, spermine (0.2 μM) blunted the stimulation of voltage-independent cation channels by Cl? removal. Spermine (0.2 and 200 μM) added to the extracellular bath solution similarly inhibited the cation conductance in Cl?-containing bath solution. The effect of 0.2 μM spermine, but not the effect of 200 μM, was rapidly reversible. Acute addition (250 μM) of a naphthyl acetyl derivative of spermine (200 μM) again significantly decreased basal cation conductance in NaCl bath solution and inhibited voltage-independent cation channels. Spermine is a powerful regulator of erythrocyte cation channel cytosolic Ca2+ activity and, thus, cell survival.     

植物基因同源重组研究现状

同源重组是普遍存在的生物学现象,从噬菌体、细菌到真核生物均有存在。它对生物的遗传与变异具有重大影响,一直是生物学家研究的热点。本文从染色体外同源重组、染色体内同源重组以及基因打靶三个方面综述了同源重组在植物方面的研究现状。从分子水平上较详尽的介绍了同源重组发生的机制以及同源重组在生物领域的应用、前景展望及其存在的局限性。     

植物基因同源重组研究现状

同源重组是普遍存在的生物学现象,从噬菌体、细菌到相传真核生物均有存在。它对生物的遗传与变异具有重大影响,一直是生物学家研究的热点。本文从染色体外同源重组、染色体内同源重组以及基因打靶三个方面综述了同源重组在植物方面的研究现状。从分子水平上较详尽的介绍了同源重组发生的机制以及同源重组在生物领域的应用、前景展望及其存在的局限性。     

Promotion and Inhibition of Inflorescence Growth by Long Days in Short-day Plants

Results of previous investigators have indicated that long periodsof light intercalated between inductive short-day cycles havean inhibitory effect on inflorescence growth in short-day plants.The present experiments show that such light periods can eitherpromote or inhibit inflorescence growth in Xanthium pemtsylvanicumand Chenopodium amaranticolor depending on their previous degreeof induction. Intercalated light exerts an inhibitory influence on the inductiveprocesses occurring during the dark period which follows itwhen unifoliate Xanthium plants have been previously exposedto not more than one short day and when fully foliated Chenopodiumplants have been previously exposed to not more than one ortwo short days. When plants are more strongly induced initially,an intercalated light period has a very marked promoting effecton the dark period succeeding it. In Xanthium this stimulatoryeffect increases with the duration of the light period up toan optimum of approximately 80 hours. It is suggested on the basis of available evidence that thepromotive effect of such intercalated light possibly affectsthe sensitivity of the apex to inductive stimuli and that itsinhibitory effect acts on the inductive processes occurringin the leaves.     

The Carbohydrate Nutrition of Tomato Roots: VI. The Inhibition of Excised Root Growth by Galactose and Mannose and its Reversal by Dextrose and Xylose

The addition of 0.01–0.015 per cent. galactose or 0.005–0.01per cent, mannose reduces by 50 per cent, the linear growthof excised tomato roots cultured in a I per cent, sucrose medium.An addition of 0.03–0.04 per cent, of either sugar causesnot less than a 90 per cent, inhibition of growth. The survivalof meriste-matic activity is higher in presence of fully inhibitoryconcentrations of mannose than of galactose. Roots inhibitedby galactose are distinguishable from those inhibited by mannose. The inhibitory effect of concentrations of galactose up to 0.15per cent, and of mannose up to 0.4 per cent, can be fully antagonizedby the simultaneous addition to the culture medium of dextrose.The minimum ratio of dextrose: inhibitory sugar for maximumantagonism of the growth inhibition is with galactose 5: 1 andwith mannose 3.5: 1. Growth of roots in a dextrose-containingmedium does not protect them from subsequent inhibition by eithergalactose or mannose. d-xylose has significant activity as an antagonist of mannoseinhibition and even more so of galactose inhibition. However,the restoration of growth achievable from the addition of xyloseis not comparable with that resulting from the addition of dextrose.The inhibition of growth by xylose is not alleviated by thesimultaneous addition of dextrose. Maltose has low activityas an antagonist of galactose and mannose inhibition. All othersugars tested and the sugar alcohols corresponding to galactoseand mannose were quite inactive as antagonists of the growthinhibition by these two sugars. Mixtures of partially inhibitory concentrations of galactoseand mannose were less inhibitory than their more inhibitorycomponent. The concentration of dextrose required to reversethe inhibitory activity of such mixtures was not greater thanthe minimum concentration required to antagonize the actionof the more inhibitory component. The antagonism of galactose inhibition by dextrose is not dueto dextrose impeding galactose uptake.     

Growth Inhibition by Purine Derivatives and Its Reversal by Pyrimidine Derivatives in a Mutant of Escherichia coli K12

An adenosine-sensitive mutant was isolated from Escherichia coli K12 derivative strain C600. This mutant (designated as PS100) grew slower than parental strain C600in a minimal medium, and its growth was completely inhibited by addition of all kinds of purine bases, nucleosides and nucleotides tested. On the other hand, this growth inhibitory effect of purine derivatives was reversed by co-addition of uridine to the medium. Other pyrimidine derivatives such as uracil, UMP,cytosine, cytidine, CMP and thymidine were also effective for this reversal. The mutant strain, PS100, showed a lower level (7%) of activity for orotate phosphoribosyltransferase than strain C600 did, and accumulated orotic acid in the growth medium. Lysogenization of strain PS100 with λ transducing phage containing the gene for orotate phosphoribosyltransferase (pyrE) resulted in restoration of the activity for orotate phosphoribosyltransferase and removal of growth inhibition by purine derivatives.     

Uptake of Homologous Series of p-n-Alkylphenols by Phytopathogenic Fungi

Uptake of homologous series of p-n-alkylphenols by fungi from aqueous phase was studied using spores of Piricularia oryzae and Gibberella fujikuroi, and mycelia of P. oryzae as test organisms.

Process of uptake seemed to be physical, because dead cells took up as much phenol as did living cells. Amount of phenol taken up by fungal cells equilibrated with concentration of remaining phenol in external aqueous phase. Uptake was found to increase with increasing alkyl side chain length, and solubility of the homologous series decreases at higher rate than uptake increases. Uptake of higher homologue is not supposed to reach the level enough to inhibit growth of fungi, on account of its slight solubility.

These results explain the reason why antifungal activity of p-n-alkylphenol increases with increasing alkyl chain length up to a certain homologue, and decreases for the higher members.     

Inhibition of Gene Expression by Homologous Double-Stranded RNA in a Drosophila melanogasterCell Culture

Specific inhibition of gene expression by exogenous homologous double-stranded RNA (dsRNA) in invertebrates and in the early development of vertebrates is termed RNA interference. Cultured cells were cotransfected with reporter plasmids and dsRNA. The inhibitory effect on reporter gene expression depended on the extent of homology between dsRNA and the target gene. RNA interference was also studied in cells cotransfected with plasmids directing synthesis of sense and antisense RNAs. Production of antisense RNA only slightly inhibited expression of the reporter gene. Simultaneous expression of both sense and antisense RNAs caused by cotransfection by corresponding plasmids did not inhibit expression of the reporter construct.     

Growth and Division of Single Cells of Higher Plants in Vitro

The cultivation of single cells of Nicotiana tabacum L. var. "Samsun" and Phaseolus vulgaris L. var. "Early Golden Cluster" on a thin agar layer in Petri dishes is described. Under these conditions about 20 per cent of the cells divided repeatedly and established tissue clones which could be isolated and maintained as growing tissue cultures. It was possible also to follow the successive divisions of isolated cells and to observe their behavior during cytogenesis under the microscope.     

Light-controlled Cycocel Reversal of Coumarin Inhibition of Lettuce Seed Germination and Root Growth

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by coumarin and these inhibitions were reversed by Cycocel. 2.53 × 10³ M Cycocel reversed the inhibition of seed germination by 6.8 × 10⁴ M coumarin. and 6.32 × lO^?4 M Cycocel reversed the inhibition of root elongation by 3.4 × 10³ M coumarin. No other analogs of Cycocel reversed these coumarin induced inhibitions of growth. Cycocel reversal of coumarin inhibition of lettuce seed germination occurred in red light but not in far-red light or darkness. The red-far-red system was photoreversible. Cycocel and kinetin appear to act similarly in reversing coumarin inhibition of germination. Gibberellin A₃ and IAA were unable to reverse these coumarin induced inhibitions. A common mechanism is suggested for Cycocel reversal of coumarin and lAA inhibition of growth.     

Reversal of Copper Inhibition in Chloroplast Reactions by Manganese

In the Mehler reaction, a Hill reaction utilizing molecular oxygen as the electron acceptor, rates of net oxygen uptake are stimulated by added manganous ions. Both whole cell photosynthesis and the Mehler reaction are inhibited by copper. Copper inhibition of the Mehler reaction can be reversed by manganese salts. Glutathione. which alone has no effect on Mehler reaction rates, enhances the effect of manganese in reversing copper inhibition. The effects of added Cu²⁺, Cu²⁺ and Mn²⁺, or Cu²⁺, Mn²⁺, and glutathione exhibit no induction phenomena when measured manometrically. Furthermore, the order of addition of these factors is unimportant: final rates are dependent only on the composition of reaction mixtures. Compared to the Mehler reaction, conventional Hill reactions are less sensitive to copper poisoning, while certain chloroplast mediated photoxidations (e.g. the photoxidation of diketogulonic acid) are far more sensitive. In all of the chloroplast mediated photoreactions tested, manganese is effective in reducing the sensitivity to copper poisoning.     

高等植物花生长和花色素苷生物合成的信号调控

介绍了赤霉素、光和糖信号对花生长和花色素苷生物合成过程的调控及调控机制的研究进展。     

Reversal Effect of Potassium Ion on Microbial Growth Inhibition by Combinations of NaCl,Ethanol and Perillaldehyde

The glutamate racemase (EC 5.1.1.3) gene of a lactic acid bacterium, Pediococcus pentosaceus, was cloned into Escherichia coli C600 with a vector plasmid, pBR322. The requirement of l-glutamate for the growth of E. coli in the minimum medium containing d-glutamate and the formation of a red pigment in a coupled enzyme reaction mixture were used to select clones expressing glutamate racemase activity. Glutamate racemase overproduced as 0.3— 2.0% of the total soluble proteins in a clone carrying the plasmid pICR221, 10.3 kb of DNA, was purified from cell extracts about 130-fold to homogeneity. The purified enzyme has a molecular weight of about 40,000 and is a single polypeptide chain. Glutamate is the sole substrate for the enzyme. Unlike many other amino acid racemases, glutamate racemase is devoid of cofactors: there is no evidence for pyridoxal 5’-phosphate or FAD in the ultraviolet spectrum of the purified enzyme, and the enzyme is not inactivated by carbonyl reagents such as hydroxylamine and sodium borohydride.