Differences in Auxin Level Detected Across Geostimulated Dandelion Peduncles: Evidence Supporting a Role for Auxin in Geotropism

Using the -pyrone fluorescence method it was established thatsignificant differences in IAA level across the Taraxacum pedunclewere detectable after both 20 min and 2 h of geostimulation. Taraxacum officinate, dandelion, geotropism, indol-3yl-acetic acid, auxin     

Indolyl-3-acetic Acid and Ethylene Levels in Ripening Apple Fruits

Indolyl-3-acetic acid (IAA) levels in apple (Malus domesticaBorkh.) fruits were determined fluorimetrically after formationof 2-methylindolo--pyrone in purified extracts. The propertiesof the fluorescent products in apple samples were identicalwith those of authentic IAA. The assays were performed on samplesof cortex with or without peel from the varieties James Grieveand Worcester Pearmain during the last 50—70 d of theirdevelopment on the tree. At the same time the ethylene concentrationin the core cavity of the fruits was measured as a guide tothe progress of ripening. IAA concentration showed a 3—4-foldincrease prior to the rapid rise in ethylene concentration butfell to about its original level as this rise occurred. IAAwas also measured in the seeds of James Grieve apples, whereit rose to a peak concentration and declined before the peakobserved in the fleshy tissue of the fruit. IAA in the seedsincreased markedly after 15 d storage of the fruit harvested136 d after full bloom.     

Criteria for Assessing the Accuracy of the Pyrone Fluorimetric Assay for Indole-3-acetic Acid

The effects of scattered light and the presence of contaminatingfluorophores on the sensitivity and accuracy of the pyrone fluorimetricassay for indole-3-acetic acid (IAA) were investigated. Withextracts from plant tissues sources of ambiguity in the fluorescencemeasurements were established. Criteria, based on the fluorescencespectra and kinetics of change of fluorescence intensity ofthe pyrone derivative, are presented for assessing the accuracyof IAA estimations using this technique.