M. C. Elliott

Endogenous and Exogenous Auxin in the Control of Root Growth

The endogenous indol-3yl-acetic acid (IAA) of detipped apical segments from roots of maize (cv ORLA) was greatly reduced by an exodiffusion technique which depended upon the preferential acropetal transport of the phytohormone into buffered agar. When IAA was applied to the basal cut ends of freshly prepared root segments only growth inhibitions were demonstrable but after the endogenous auxin concentration had been reduced by the exodiffusion technique it became possible to stimulate growth by IAA application. The implications of the interaction between exogenous and endogenous IAA in the control of root segment growth are discussed with special reference to the role of endogenous IAA in the regulation of root growth and geotropism.

Acid growth effects in maize roots: Evidence for a link between auxin-economy and proton extrusion in the control of root growth.

The role of proton excretion in the growth of apical segments of maize roots has been examined. Growth is stimulated by acidic buffers and inhibited by neutral buffers. Organic buffers such as 2[N-morpholino] ethane sulphonic acid (MES) — 2-amino-2-(hydroxymethyl)propane-1,3 diol (Tris) are more effective than phosphate buffers in inhibiting growth. Fusicoccin(FC)-induced growth is also inhibited by neutral buffers. The antiauxins 4-chlorophenoxyisobutyric acid (PCIB) and 2-(naphthylmethylthio) propionic acid (NMSP) promote growth and H+-excretion over short time periods; this growth is also inhibited by neutral buffers. We conclude that growth of maize roots requires proton extrusion and that regulation of root growth by indol-3yl-acetic acid (IAA) may be mediated by control of this proton extrusion.

Endogeneous levels of indole-3-acetic acid and abscisic acid during the rooting of Cotinus coggygria cuttings taken at different times of the year

Cuttings of Cotinus coggyria cv Royal Purple rooted well in the spring but not at all later in the season. Levels of free and conjugated IAA and ABA were measured in cuttings taken at different times of the year. Hormones were measured in the leaf, the upper stem and the lower stem (rooting zone). In cuttings taken in early June the level of IAA was much higher than that of conjugated IAA. In late July the opposite was found. No significant differences in ABA levels were found although the ABA/IAA ratio changed dramatically.

Indol-3yl-acetic acid in roots of Zea mays

Abstract Indol-3yl-acetic acid was identified in extracts of sterile roots of Zeamays seedlings by means of TLC, chromogenic reactions, GLC and GC-MS.

Auxin gradient along the root of the maize seedling.

Abstract[5-3H]Indol-3yl-acetic acid (IAA) applied to the shoot apices of intact 6-day-old maize (Zea mays L.) plants moved into the primary root and accumulated at the root apex. IAA from the shoot could partially satisfy the requirement of the primary root for IAA for growth.

Simultaneous analysis of indole-3-acetic acid and detection of 4-chloroindole-3-acetic acid and 5-hydroxyindole-3-acetic acid in plant tissues by high-performance liquid chromatography of their 2-methylindolo-α-pyrone derivatives

Abstract The use of high-performance liquid chromatography in the reversed-phase mode coupled to a spectrophotofluorimetric detector allowed the selective detection of acidic indoles possessing a C-3 methylene side chain, following the reaction of a purified plant extract with acetic anhydride. Of these acidic indoles, only 4-chloroindole-3-acetic acid and 5-hydroxyindole-3-acetic acid were found to have fluorescence activity greater than 1% of that of indole-3-acetic acid, and good separation of these derivatives was obtained by high-performance liquid chromatography. In purified tissue of both Pinus sylvestris and Chamaecyparis lawsoniana, two fluorescing peaks were separated following derivatisation. The first had an identical fluorescence emission spectrum and retention time in high-performance liquid chromatography to the 2-methylindolo-α-pyrone derivative of indole-3-acetic acid. The second is so far unidentified. The presence of such unidentified compounds in extracts analysed by the standard spectrophotofluorimetric method would lead to an overestimate of the levels of indole-3-acctic acid. The use of high-performance liquid chromatography in the analysis of derivatised acidic indoles is discussed in relation to other published modifications of the method.

Welcome to Agriculture & Food Security

Editorial Senior scientists from many countries have come together to meet the need for an open access research journal that focuses explicitly on agriculture, the condition of food security and the critical linkages between these topics. In the 21 century, we recognize the dual role of agriculture as our species’ lifeline for food and essential materials, as well as the dominant form of terrestrial planetary care, and the journal will facilitate the dissemination of information in this vitally important area of research. Norman Borlaug (1914–2009) was awarded the Nobel Peace Prize in 1970 for initiating the Green Revolution in agriculture which increased agricultural production so successfully as to enable some one billion people, who would otherwise have died from starvation, to thrive. That said, it must be noted that in his Nobel Peace Prize Acceptance Speech (December the 11th, 1970) [1], he observed that: “The green revolution has won a temporary success in man’s war against hunger and deprivation; it has given man a breathing space. If fully implemented, the revolution can provide sufficient food for sustenance during the next three decades. But the frightening power of human reproduction must also be curbed; otherwise the success of the green revolution will be ephemeral only.” The harsh reality of this warning was recognised in the early part of 2008 when the price of wheat and maize doubled and that of rice tripled, leading to food riots in 20 countries. The Editors bring diverse perspectives to the challenge Norman Borlaug and his generation left in the wake of the Green Revolution, but several points are inescapably clear. There is broad agreement that food security is a goal of paramount importance in the 21 century, and that food and food systems are critically important to humans far beyond the physical survival they provide. A sharp focus on productivity of familiar crops will continue to be essential using all technical and conceptual approaches that make sense to increase yields, improve crop and livestock efficiencies and overall agricultural systems outputs, and

Phytohormone changes during storage root growth in Beta species

The physiological and morphological factors necessary for efficient accumulation of sucrose in sugar beet (Beta vulgaris L.) are considered in relation to potential uses of plant growth regulators to modify the anatomy of storage roots so as to increase sucrose content and yield. The percentage of sucrose in root fresh and dry matter is closely related to root structure. Sugar beet, mangold and chard are three sub-species of Beta vulgaris that differ considerably in their anatomy, assimilate partitioning, sucrose concentration and root dry matter yield. The concentrations of indole-3-acetic acid (IAA), abscisic acid (ABA) and cytokinins were measured during the growth of the storage root in each of these cultivars. Correlations were found between the phytohormone levels and the formation of secondary cambia and their subsequent cell division and expansion activity.

Effects of Ri plasmid rol gene expression on the IAA content of transformed roots of Solanum dulcamara L.

The effects have been investigated of various combinations of rol genes, together with Ri plasmid TR-DNA transcripts 1 and 2, upon free IAA levels in transformed roots of Solanum dulcamara L. Differences between the IAA levels were observed, including a highly significant (p=0.01) difference between the IAA levels of rol− TR+ and rol ABC+ TR+ transformed roots. Possible mechanisms are discussed for the regulation of free IAA levels by rol gene products.

Auxin structure/activity relationships: Aryloxyacetic acids

Abstract The results of self-consistent field molecular orbital calculations on auxins of the aryloxyacetic acid type do not support the ‘charge separation’