H. R. Lerner

Essential Oils as Allelochemicals and Their Potential Use as Bioherbicides

Essential oils were extracted from 32 aromatic plants and evaluated for allelopathic properties. The major components of the oils were identified by gas chromatography and GC-MS. Extracts from Origanum syriacum, Micromeria fruticosa, and Cymbopogon citratus were selected for further study. The germination of several species, including wheat, was strongly inhibited by essential oils when applied at 20–80 ppm. Essential oils mixed with the top 0.5 cm of soil inhibited germination of wheat and Amaranthus seeds. This effect depended on the type of soil. The possible use of essential oils as herbicides is discussed.

Evidence for conformational changes in grape catechol oxidase

Abstract A rapid, 4–10-fold, activation of grape catechol oxidase by a short exposure to acid pH or urea is demonstrated. Activation was either reversible or irreversible, depending on length and type of treatment. The change in activity of the enzyme is due primarily to an increase in V max , while the affinity for 4-methylcatechol decreases and that for O 2 increases. Activation occurs in intact chloroplasts as well as in a partially purified enzyme preparation. Activation was apparently due to conformational changes in the enzyme. O 2 concentration appeared to control enzyme activity, presumably by an O 2 induced conformational change. Irreversible activation was accompanied by changes in the electrophoretic mobility of the enzyme.

Purification and properties of laccase from Botrytis cinerea

Abstract The partial purification of an extracellular laccase from Botrytis cinerea is described. Specificity of the enzyme, its Km for a number of substrates and sensitivity to some inhibitors are described. The enzyme is a typical laccase but has an exceptionally low pI and great stability to acid pH. On gel electrophoresis two isoenzymes could be detected.

Biotransformation of constituents of essential oils by germinating wheat seed

Wheat seeds, when exposed to essential oils, are able to metabolise certain monoterpenes. The actual amounts of the compounds and their derivatives in the endosperm and embryo of wheat seeds, after exposure to the monoterpenes were determined. Neral and geranial, which are the constituents of citral, are reduced and oxidised to the corresponding alcohols and acids. Similarly citronellal, pulegone and carvacrol are converted partly to the corresponding reduction and oxidation products. The aromatic compound vanillin is partly reduced to vanillyl alcohol or oxidised to vanillic acid. In all cases it seems that part of the compounds applied are degraded, as indicated by the inability to account for all the compounds, which were supplied to the germinated seeds. In most cases the derivatives of the essential oil applied were less toxic than the parent compound. The possible role of non-specific enzymes by which the compounds are oxidised or reduced is discussed.

Phenylhydrazine, a specific irreversible inhibitor of catechol oxidase

Abstract Phenylhydrazine is shown to specifically inhibit a number of catechol oxidases from plant tissues. A laccase-like enzyme from peaches is not inhibited while ascorbic oxidase is only partly inhibited by relatively high concentrations of the inhibitor. Inhibition is non-competitive and irreversible and increases with time of incubation. Inhibition is dependent on the presence of oxygen during incubation of the enzyme with inhibitor but independent of the presence of the phenolic substrate.

ADAPTATION VERSUS PRE-EXISTING RESISTANCE: AN INTERGENOTYPE ANALYSIS OF THE RESPONSE OF SORGHUM BICOLOR TO SALINITY

ABSTRACT Developmental and physiological responses of 11 Sorghum bicolor (L.) Moench genotypes exposed for 3 weeks to a 150 mM NaCl-pretreatment were studied. Following the pretreatment, exposure to 300 mM NaCl resulted in a gradient of response between “adaptation to salinity” (increase in salinity tolerance) and “pre-existing resistance” (maintenance of original salinity tolerance). Level of adaptation of each genotype was quantified by determination of the mean relative growth rate of the shoot at 300 mM NaCl ( ). There was a positive correlation between and the following parameters during the process of adaptation: inhibition of growth, decrease of the shoot:root ratio, and shoot Na+ uptake. There were more pronounced physiological perturbations during adaptation than during the pre-existing resistance response to salinity. During the first 25 days of exposure to NaCl, inhibition of growth and shoot Na+ concentration were not correlated. The much lower value for the intergenotype coefficient of variat...

THE RESPONSE OF PLANTS TO SALINITY: FROM TURGOR ADJUSTMENTS TO GENOME MODIFICATION

ABSTRACT The parameters affected by salinity in salt-sensitive plants are reviewed. Turgor is the potential energy which powers extension growth, but is not a parameter which controls the growth process. Cell expansion is affected by phytohormones, and salinity modifies the phytohormonal balance of the plant; one of the major effects of salinity on growth results from a modification of the phytohormonal balance. Exposure to salt of certain plant genotypes, under appropriate conditions, results in an increase in salt resistance, which has been termed adaptation. The capacity to adapt is limited to a precise period of development. The process of adaptation is accelerated by abscisic acid and inhibited by cytokinin. It is a genetic character which is not a property of all genotypes. Adaptation is transmitted to the next generation, which suggests that it involves a modification of the genome. In plants, genome organization and expression are modified during development and under various types of environmenta...

Reaction mechanism of grape catechol oxidase—a kinetic study

Abstract The initial velocity of the oxidation of 4-methylcatechol by grape catechol oxidase was determined. The kinetic analysis indicates that first there is random binding of an oxygen and a 4-methylcatechol molecule to the enzyme. Then one product molecule is released prior to the binding of second 4-methylcatechol molecule which is followed by the release of a second product molecule. The true K m values were determined; they were found to be 0.5 mM for oxygen and 17 mM for 4-methylcatechol.

INFLUENCE OF THE MODE OF SALINIZATION ON REPRODUCTIVE TRAITS OF FIELD-GROWN PROGENY IN SORGHUM BICOLOR

ABSTRACT The offspring of Sorghum bicolor (L.) Moench plants exposed to 150 mM NaCl eight or twenty-one days following germination were grown in field conditions, and were irrigated with non-saline water. As compared to the offspring of non-treated plants, the progeny of plants early-exposed to NaCl displayed an increase in shoot dry weight and stem height, but some of them showed a significant decrease in fertility. Similar changes were observed, but to a lesser extent, in the offspring of plants late-exposed to salinity. A similar increase in phenotypic variability was observed in populations of progeny from early-and late-treated plants. After verifying that the changes observed did not result from an artifactual selection, it was concluded that the NaCl treatment is able to influence characters expressed during the late development of the plant progeny. The nature of the induced change is discussed in relation to the plant response, adaptation or resistance, induced by the early or late exposure to sa...