L.A. Wilson

Stimulatory and inhibitory effects of Scopoletin on IAA oxidase preparations from sweet potato

Abstract IAA oxidase preparations from sweet potato (Ipomoea batatas) roots and etiolated shoots catalysed the disappearance of IAA in the absence of added H2O2, manganese and phenolic cofactors. Scopoletin inhibited IAA oxidase activity at high concentrations (12·5–250 nmol/ml) but stimulated activity at low concentrations (0·25–10·00 nmol/ml); these effects were dependant on the concentration of IAA and enzyme. Competitive inhibition of IAA oxidase activity by scopoletin is discussed and the compound is described as the most potent, naturally occurring stimulator of IAA oxidase activity so far reported. A vital role in the in vivo regulation of IAA levels in plants is suggested for this compound.

Dormancy responses to post-harvest application of growth regulators in Dioscorea species: I. Responses of bulbils, tubers and tuber pieces of three Dioscorea species

The effects on dormancy of post-harvest application of growth regulators to bulbils, tubers and tuber pieces of tropical Dioscorea species were examined. Abscisic acid, kinetin, indole acetic acid and 2-chloroethyltrimethylammonium chloride were found to have little or no effect on either shoot or tuber-root production, while ethrel greatly promoted tuber-root production with little or no effect on shoot development. The germination of slices of tubers of D. alata was delayed by maleic hydrazide but there was no effect on intact tubers of D. alata and D. esculenta . Treatment with 2,4-dichlorophenoxyacetic acid caused massive root and callus development along with delay in shoot development, while gibberellic acid occasioned marked extensions in the dormant period.

Effects of chlorogenic and caffeic acids on IAA oxidase preparations from sweet potato roots

Abstract IAA oxidase preparations from sweet potato ( Ipomoea batatas ) roots oxidised IAA in the absence of added phenolics. Activity was optimal around pH 6·8 and a minor pH optimum occurred around pH 4·3. Both chlorogenic and caffeic acids inhibited IAA oxidase activity at high concentrations (0·6–5·7 nmol/ml) but stimulated enzyme activity at low concentrations (0·10-0·55 nmol/ml); these effects were dependent on IAA and enzyme concentration and on pH. The activities of both substances are compared with those of other phenolics known to stimulate and inhibit plant IAA oxidases.

Tuber development, storage and germination in yams (Dioscorea spp.) in response to pre-harvest application of plant growth regulators

When pre-harvest foliar applications of growth regulators were made to vines of Dioscorea esculenta cv. Chinese Yam and D. alata cv. White Lisbon there were no obvious effects on tubers of D. alata , but dramatic effects on tuber development, storage and germination were obtained with D. esculenta tubers. Gibberellic acid caused marked extensions in tuber dormancy, 2,4-dichlorophenoxyacetic acid resulted in marked callus development, delayed germination and abnormal shoot and root development and indole acetic acid resulted in fingering of the tubers. It was concluded that there was potential for commercial exploitation of pre-harvest gibberellic acid treatments in extension of dormancy in Chinese Yam tubers and that the lack of response of D. alata tubers to foliar application of growth regulators warranted further investigation.

IAA oxidase preparations from sweet potato roots

Abstract IAA oxidase preparations from sweet potato roots have major and minor pH optima, which were related to the pH of phosphate-citrate or phosphate buffers used to solubilize acetone precipitates in the course of enzyme preparation. Acetone precipitates were solubilized at five pHs and two representative enzyme types, 7·0 and 4·5 enzymes, with high (pH 5·8–6·8) and low (pH 3·6–4·6) major optima, respectively, further investigated. Both 7·0 and 4·5 enzymes had single pH optima at pH 4·5 in scopoletin stimulated IAA oxidase reactions. The pH optima and specific activities of IAA oxidase, peroxidase and phenolase were compared in 7·0 and 4·5 enzyme preparations and IAA oxidase inhibition by thiourea and sodium azide reported. The occurence of different IAA oxidase pH optima in sweet potato root and other plant preparations is discussed.

IAA Oxidase preparations from fresh and aged Ipomoea batatas tuber discs

Abstract IAA oxidase preparations from fresh sweet potato tuber discs oxidized IAA only in the presence of added phenolic cofactors, and the pH optimum for enzyme activity depended on the cofactor used. Ageing of tuber discs, either by aeration in distilled water or by incubation on moist filter paper, resulted in increased peroxidase and phenol-stimulated IAA oxidase activities, as well as the development of IAA oxidase activity in the absence of added cofactors. High phenolase activity of fresh tuber discs decreased considerably with ageing. Phenol-stimulated IAA oxidase activity reached maximal levels before IAA oxidase activity in the absence of added cofactors. Enzyme preparations from aged tuber discs had double pH optima, similar to those previously described for sweet potato root IAA oxidase preparations. IAA in the concentration range 10 −4 to 10 −2 M inhibited the increase in peroxidase and IAA oxidase activities with ageing. DCP-stimulated IAA oxidase activities in preparations from both fresh and aged sweet potato tuber discs were inhibited by manganous ion.

Prediction of Soil Cadmium Bioavailability to Cacao (Theobroma cacao L.) using Single-Step Extraction Procedures

In this study, complexation extractants ammonium bicarbonate diethylene triamine pentaacetic acid (AB-DTPA), diethylene triamine pentaacetic acid (DTPA), and ethylene diamine tetraacetic acid (EDTA) and mild cation-exchange extractants calcium chloride (CaCl2) and ammonium nitrate (NH4NO3) were used to evaluate the bioavailability of soil cadmium (Cd) to cacao in the field. Among the five extractants, the extractable Cd generally followed the order EDTA > DTPA > AB-DTPA > CaCl2 > NH4NO3. Correlation analysis was done between the extractable Cd in soil and total Cd content of cacao tissues (nibs, shells, leaves, and pods). The Cd extracted by CaCl2 and NH4NO3 was significantly (P < 0.05) correlated with some of the tissues but their Pearson correlation coefficients were weak. In contrast, extractants AB-DTPA, DTPA, and EDTA showed stronger, significant correlations to the Cd concentration in all four tissues. Overall, regression analysis demonstrated that AB-DTPA, DTPA, or EDTA can be used to predict bioavailable Cd in soils for cacao. Of these, AB-DTPA and DTPA both showed the strongest correlations compared to EDTA. However, the ease of preparation and the superior shelf-life of DTPA over AB-DPTA make it the preferred reagent for Cd bioavailability extractions from cacao soils and is currently being used to develop cost-effective soil treatments to reduce bioavailable Cd to cacao plants.