The physiological significance of phenylacetic Acid in abscising cotton cotyledons.
The physiological role of phenylacetic acid (PAA) as an endogenous regulator of cotyledon abscission was examined using cotton (Gossypium hirsutum L. cv LG 102) seedlings. Application of 100 micromolar or more PAA to leafless cotyledon abscission-zone explants resulted in the retardation of petiole abscission and a decrease in the rise of ethylene evolution that normally accompanies aging of these explants in vitro. The partial inhibition of ethylene evolution in these explants by PAA was indirect since application of this compound stimulated short-term (<24 hours) ethylene production. PAA treatment partially suppressed the stimulation of petiole abscission elicited by either ethylene or abscisic acid. Both free and an acid-labile, bound form of PAA were identified in extracts prepared from cotyledons. No discernible pattern of changes in free or bound PAA was found during the course of ethylene-induced cotyledon abscission. Unlike indole-3-acetic acid, transport of PAA in isolated petiole segments was limited and exhibited little polarity. On the whole, these results are not consistent with the direct participation of PAA in the endogenous regulation of cotyledon abscission.
Gas Chromatographic Identification and Quantitative Estimation of Natural Auxins in Developing Plant Organs
Evidence indicating the natural occurrence of the auxins, indole-3-acetic acid and phenylacetic acid, in a range of higher plants has been obtained from bioassay examination and gas chromatographic analysis of acidic ether fractions from vegetative shoots of these plants. Quantitative estimation of the relative amounts of each auxin in the different shoots was also achieved by gas chromatography. As part of a comprehensive study to examine the changes in amounts of different growth-regulating substances in plant organs during their growth and development, the identification and quantitative estimation of the auxins present in developing tobacco leaves have been determined by gas chromatography. The results demonstrate that in expanding leaves there is a close correlation between the endogenous levels of several auxin substances and the subsequent growth rate of this plant organ.
The Biosynthesis of Phenylacetic Acids in the Blue-Green Alga Anacystis nidulans: Evidence for the Involvement of a Thylakoid-Bound ʟ-Amino Acid Oxidase
Abstract Phenylacetic acid and p-hydroxyphenylacetic acid are formed upon incubation of photosynthetic membranes from the prokaryotic alga Anacystis nidulans with ʟ-phenylalanine and ʟ-tyrosine, respectively. The corresponding phenylpyruvic acids act as intermediates as shown by trapping them as the stable oximino acids. The first step in this reaction sequence appears to be catalyzed by a thylakoid-bound ʟ-amino acid oxidase. Already existing evidence concerning phenylacetic acid formation at thylakoid membranes of higher plants via an ʟ-amino acid oxidase and the results obtained with A. nidulans give another example of aromatic amino acids between chloroplasts and blue-green algae.