Auxin: regulation, action, and interaction.

Our understanding of the biology, biochemistry, and genetic development of roots has considerably improved during the last decade ([Smith and Fedoroff, 1995][1]; [Flores et al., 1999][2];[Benfey and Scheres, 2000][3]). In contrast, the processes mediated by roots in the rhizosphere such as the

Root exudation and rhizosphere biology.

Effect of exogenous salicylic acid under changing environment: a review

Microorganisms in soils and waters convert many synthetic organic chemicals to inorganic products. Other compounds are transformed only by cometabolism. These microbial processes may lead to environmental detoxication, the formation of new toxicants, or the biosynthesis of persistent products. Type reactions are proposed for major categories of enzymatic transformation of synthetic chemicals in soils, natural waters, and sewage. Some organic molecules are resistant to microbial attack, and explanations for the persistence of such compounds are suggested.

https://science.sciencemag.org/content/sci/211/4478/132.full.pdf

Biodegradation of Chemicals of Environmental Concern

Organochlorine (OC) pesticides are synthetic pesticides widely used all over the world They belong to the group of chlorinated hydrocarbon derivatives, which have vast application in the chemical industry and in agriculture These compounds are known for their high toxicity, slow degradation and bioaccumulation Even though many of the compounds which belong to OC were banned in developed countries, the use of these agents has been rising This concerns particularly abuse of these chemicals which is in practice across the continents Though pesticides have been developed with the concept of target organism toxicity, often non-target species are affected badly by their application The purpose of this review is to list the major classes of pesticides, to understand organochlorine pesticides based on their activity and persistence, and also to understand their biochemical toxicity

/pdf/review-article-organochlorine-pesticides-their-toxic-effects-169hh13mnc.pdf

Review Article. Organochlorine pesticides, their toxic effects on living organisms and their fate in the environment

SUMMARY

The metabolism of certain 2,6-disubstituted phenols that possess high auxin activity in the pea segment, pea curvature and tomato-leaf epinasty tests, but are much less active in the wheat cylinder test, has been investigated in wheat, pea and tomato tissue. Metabolites were identified by thin-layer chromatography and a semi-quantitative assay method was developed.



The low activity of 2,6-dihalogenophenols and inactivity of 2-halogeno-6-nitro-phenols and 3-halogeno-2-hydroxybenzonitriles in the wheat cylinder test was caused by rapid metabolic conversion of the compounds in this tissue to inactive compounds by a process involving hydroxylation of the aromatic ring in the para- position. No such inactivation occurred in pea and tomato tissues.



Evidence for a novel detoxification of nitrophenols within both pea and wheat tissue was obtained; 2-bromo–6-nitrophenol was converted via 2-bromo-6-aminophenol to N-acetyl-2-bromo-6-aminophenol.



Certain 3-halogeno-2-hydroxybenzaldehydes and corresponding aceto-phenones, although fulfilling the necessary structural and electronic criteria for auxin activity, are inactive. Metabolic studies indicate that this is because they are metabolized in wheat, pea and tomato tissues to compounds not possessing the structural requirements for auxin activity.

Studies on plant growth‐regulating substances

Light-induced inhibition of the elongation of primary roots of Zea mays seedlings is dependent upon the perception of light by the root cap. Separate exposure of detached root caps and roots from which root caps have been removed (i.e. decapped roots) to white light or darkness has shown that the elongation of a dark-exposed root to which a light-exposed root cap is attached is inhibited significantly, whilst a light-exposed decapped root to which a dark-exposed root cap is attached is not inhibited. Thus the decapped root is not capable of perceiving the growth-inhibitory stimulus of white light and its rate of elongation is greater than that of light-exposed roots with root caps still intact. However, the capacity to perceive light and, therefore, to be inhibited by it, is restored to the decapped root approximately 5 h after removal of the root cap.Abscisic acid and two unidentified growth-inhibiting compounds are present in the root caps of light-grown but not of dark-grown Zea mays seedlings and a period of 2.5-3.0 h is required for transport of the compounds, in levels effective in growth inhibition, from the root cap into the apex of the root.

The root cap and control of root elongation in Zea mays L. seedlings exposed to white light.

Plant growth-regulating activity in homologous series of $\omega $-(3-indolyl)alkanecarboxylic acids, their methyl esters, amides and nitriles has been assessed in the wheat-cylinder, pea-curvature and pea-segment tests. In wheat tissue all homologues were active except 3-indolecarboxylic acid and its corresponding ester, amide and nitrile. These compounds, together with the propio-, butyro-, valero- and capro-nitriles, were inactive in the pea tests. The breakdown of all the compounds when metabolized in wheat coleoptile and pea-stem tissues was investigated using paper chromatography, identification of metabolites being made by chromogenic tests and bio-assay. Strong evidence was obtained that $\beta $-(3-indolyl)propionic acid is itself a plant growth hormone and not a hormone precursor, and that $\beta $-oxidation of this compound within plant tissue to 3-indolecarboxylic acid, is hindered. The formation of either 3-indolylacetic or $\beta $-(3-indolyl)propionic acids from alternate homologues in the acid series is fully consistent with degradation of the side-chain by $\beta $-oxidation. All esters and amides except 3-indoleamide were readily converted within the test tissues to the corresponding acids and their activity is explicable on this basis. With the nitriles in wheat tissue, the results indicated that the terminal-CN is hydrolyzed to-COOH with all homologues except 3-indolenitrile. In pea tissue, however, only 3-indolyl-acetonitrile was hydrolyzed in this way. Evidence for $\alpha $-oxidation was obtained in wheat with all homologues except 3-indolenitrile. In pea tissue, however, only 3-indolylacetonitrile and $\zeta $-(3-indolyl)heptanonitrile were so degraded. The mechanisms underlying oxidative breakdown of the side-chain of these indole homologues are discussed. The results are shown to provide further evidence for $\beta $-oxidation of acids and $\alpha $-oxidation of nitriles within plant tissues and, in addition, it is suggested that with longer chain lengths, nitriles may also be subject to $\omega $-oxidation.

The Metabolism of 3-Indolylalkanecarboxylic Acids, and their Amides, Nitriles and Methyl Esters in Plant Tissues

The plant growth-regulating activities of homologous series of $\omega $-(4-chlorophenoxy)-, $\omega $-(2:4-dichlorophenoxy)- and $\omega $-(2:4:5-trichlorophenoxy)-alkylcarboxylic acids and of the corresponding $\omega $-(1-naphthyl)- acids have been assessed in the wheat cylinder, pea curvature and tomato-leaf epinasty tests. In most instances, an alternation in activity was observed as each series was ascended. With some series, however, although the acetic derivative was active, all higher homologues were inactive in certain tests. The results are discussed and shown to be consistent with a possible degradation of the side-chain of these acids by $\beta $-oxidation within the plant tissue. Although the evidence indicates that $\beta $-oxidase enzyme systems are present in all three types of plant tissue employed, whether or not such enzymes can degrade the side-chain of these acids appears to be related to the type of ring system and to the orientation of nuclear substituents present in the molecule. Thus, for example, 4-chlorophenoxy- and 2:4-dichlorophenoxy-acetic acids and their alternate homologues were active in all three tests, whereas in the case of the $\omega $-(2:4:5-trichlorophenoxy)- series, this typical alternation in growth-regulating activity was shown only in the wheat cylinder test. However, when solutions of alternate homologues of the latter series were pre-treated with wheat cole-optile tissue, they induced growth responses in the pea test. Furthermore, the pre-treated solution of the butyric derivative was shown by chromatographic methods to contain the acetic homologue. The growth-regulating activity of a number of 1-naphthyl-acids with alkyl substituents in the side-chain was also determined. The results are consistent with the view that substitution in the $\beta $-position of the side-chain can hinder $\beta $-oxidation of these compounds.

The Growth-Regulating Activity of Certain $\omega $-Substituted Alkyl Carboxylic Acids in Relation to their $\beta $-Oxidation within the Plant

AN epimeric mixture of the diterpenes sclareol and 13-epi-sclareol (sclareol) (Fig. 1) has been shown to constitute 10%; of the surface exudate on leaves of Nicotiana glutinosa1. Investigations into its effect on fungal growth showed that it neither inhibits the spore germination of several species of facultative pathogens in vitro nor reduces the weight of mycelium produced in liquid medium. The development of hyphae of certain species of fungi, for example Alternaria brassicicola, is, however, markedly affected by this compound. In the presence of sclareol, increased branching is induced which leads to a substantial reduction in the diameter of colonies growing on agar1. Such morphological effects could be interpreted as the result of alterations in the regulation of natural fungal growth processes. This report describes the effect of sclareol on the germination and growth of rust fungi in vitro, and the protection it can provide to plants against diseases caused by these fungi.

R. L. Wain

Papers

Studies on plant growth‐regulating substances

The root cap and control of root elongation in Zea mays L. seedlings exposed to white light.

The Metabolism of 3-Indolylalkanecarboxylic Acids, and their Amides, Nitriles and Methyl Esters in Plant Tissues

The Growth-Regulating Activity of Certain $\omega $-Substituted Alkyl Carboxylic Acids in Relation to their $\beta $-Oxidation within the Plant

Control of rust diseases by diterpenes from Nicotiana glutinosa