The Physio1ogical Activity of 2 : 6-Substituted Phenoxyacetic Acids

Anumber of 2 : 6-substituted phenoxyacetic acids in which theside chain had been substituted by ailcyl groups to form -propionic,-n-butyric and -n-valeric acids were investigated to assesstheir ability to act as growth-regulators. Besides employingstandard tedmiques of bioassay, further experiments were undertaken to determine the effects of these compounds on the vegetativegrowth and development of intact plants of Helianthus annuus. It has been established that all the compounds tested inducedcurvature in the Went pea curvature test and that without exceptionthe activity of the parent phenoxyacetic acid (2:6-dichloro-,2:4:6-trichloro-,2:6-dimethyl-, and 2:4-dichloro-6-methyl-)was increased by side chain substitution. In the Avena straight growth assay, the a 2:6-dichloro- and2:6-dimethyl- phenoxypropionic and butyric acids brought aboutstatistically significant increases in length of the coleoptilesections, when measurements were made at the end of 24 hours.Their activity was of the same order as that exhibited by a2:4-dichlorophenoxyacetic acid. Investigations were carried out on the uptake of water by sectionsof pea internode and the extension growth of Avena coleoptileaectiona when both the concentration and the length of treatmentwere varied. For some compounds it was found that over a certainrange of concentration water uptake and extension growth wereaccelerated in the initial 6–8 hours. Subsequent to this,inhibition occurred so that no significant increases above controlvalues were apparent at the end of 24 hours, and in some casesan actual loss of water or shrinkage in length took place. Itwas thus possible to demonstrate that 2:6-dimethylphenoxyaceticacid acts as a growth regulator in pea extension growth andthat 2:6-dichiorophenoxyacetic acid is active in the Avena test. The changes in the leaf area of individual pairs of leaves,together with the lengths of the internodes and shoot weightwere followed after application of measured amounts of eachcompound to the first pair of leaves of H. annuus. A numberof the 2:6-compounds were capable of modifying growth in wayssimilar to 2:4-dichlorophenoxyacetlc acid. However, much higherconcentration had to be applied in order to produce effectscomparable to those caused by the 2:4-dichloro- compound. Measurementsof the percentage of applied compound which penetrated intothe leaf showed that there were no marked differences in thisrespect between the different phenoxy acids. On the other hand,experiments in which the treated leaves were left on the plantfor varying periods of time led to the conclusion that the a: 6-substituted compounds are less readily translocated than2:4-dichlorophenoxyacetic acid.     

Efficacy and deficiencies of rapid biomonitoring in biodiversity conservation: a case study in South Africa

Rapid biomonitoring protocols, using biotic indices based on macroinvertebrate diversity to assess river ecosystem health, are widely used globally. Such quick assessment techniques are lauded for the rapid results obtained and the relatively easy protocol used to achieve an answer. However, do such quick assessments of water quality give enough information about ecosystems? Are important details being overlooked? When should a full faunal survey be used in preference? Important research programmes, including environmental impact studies, often misuse biomonitoring techniques, making influential management decisions using superficial, low-level data obtained using biomonitoring tools, inappropriate to address those management objectives. The value of using biomonitoring as a quick tool, versus a more detailed faunal assessment, is considered here. The assessment of teloganodid mayfly fauna occurring in South African rivers provides an example of the value of detailed studies versus superficial family level investigations, showing that a rapid biomonitoring approach should not be used as a shortcut when a more detailed survey is needed. Each situation should be assessed for its own merit in a given set of project circumstances. A checklist of criteria is presented, giving guidance on when rapid biomonitoring alone is valuable and when more detailed assessments would give a more relevant result.     

Hydroxyproline and Peroxidases in Cell Walls of Pisum sativum: Regulation by Ethylene

Purified cell-wall preparations from the epicotyl of etiolatedPisum sativum contain covalently bound peroxidases and hydroxyproline-richproteins. Towards the end of cell elongation there is a largerise in these wall components and thereafter a continuing slowrise which is associated with increasing age of tissue. Ethyleneat concentrations of 0.1 ppm or more increases both peroxidaseactivity and hydroxyproline levels in the walls, the greatestresponse occurring in immature tissue including the apical hook.Growth of these tissues is highly sensitive to ethylene whichcauses an inhibition of elongation in extending cells and anenhanced lateral cell expansion. We suggest that the effectsof ethylene on wall-bound peroxidase and hydroxyproline areimplicated in the ethylene regulation of cell growth. The covalently bound wall peroxidase was found to be extremelystable and to contain unique isoenzymes which do not occur ineither the cytoplasm or in the peroxidase which is ionicallybound to walls. Ethylene increases peroxidase activity in boththe cytoplasmic and the ionically bound wall fractions, butthere is little or no increase in their hydroxyproline content.The possible relationships between covalently bound wall peroxidaseand hydroxyproline are discussed and we speculate that thisperoxidase may be involved in the hydroxylation of proline inthe walls.     

Oxidation of Arsenite by a Soil Isolate of Alcaligenes

A strain of Alcaligenes , isolated from soil and grown in nutrient broth in the presence of arsenite, possessed the ability to oxidize arsenite to arsenate. Washed cell suspensions consumed one-half mol of oxygen/mol of arsenite and produced arsenate. The optimum pH for arsenite oxidation was 7.0. The K_m for arsenite was 1.5 × 10^-4 M and V _max was 6.7 μl of oxygen/min. The arsenite-oxidizing enzyme system was induced by growth in arsenite. Response of the arsenite-oxidizing enzyme system to respiratory inhibitors suggested that electrons resulting from arsenite oxidation by an oxido-reductase with a bound flavin are transferred via cytochrome c and cytochrome oxidase to oxygen. The presence of the cytochromes in crude extract was confirmed by spectral measurements.     

Leaf Development in Lolium temulentum L.: Progressive Changes in Soluble Polypeptide Complement and Isoenzymes

Ougham, Helen J., Jones, Thomas W. A. and Evans, Mair LL. 1987.Leaf development in Lolium temulentum L.: progressive changesin soluble polypeptide complement and isoenzymes.—J. exp.Bot. 38: 1689–1696. The spectrum of soluble polypeptides extracted from segmentsof the developing 4th leaf of Lolium temulentum simplified withincreasing distance from the leaf base. Most of the metabolicallyimportant isoenzymes analysed also exhibited gradients of activitywith respect to distance from the base, and in some cases twoor more contrasting gradients were observed for a given enzyme. Key words: Gradients, isoenzymes, leaves, Lolium temulentum,, soluble polypeptides