Fusicoccin effects on maize roots: relationship between malate accumulation and elongation

Abstract In maize root segments malate accumulation, measured by gas chromatography, was found to be strongly promoted by fusicoccin (FC). The effects of FC on root elongation and proton extrusion were also analysed. Growth rates and extrusion rates were found to be proportional to malate content. Other organic acids were analysed, but no significant changes were found following FC treatment. The effects of FC are discussed in relation to the regulation of metabolism and growth.     

Effects of Light on the Georeaction and Growth Inhibitor Content of Roots

The positive geotropic response of the apical segments prepared from the primary roots of Zea mays depends upon at least one growth inhibitor, produced by the root cap, moving basipetally into the extending zone of the root in which it accumulates in the lower part. Anjou maize reacts in both darkness and light while Kelvedon maize is, for the first few hours, geotropic only in light. The production (or activity) of the growth-inhibiting substance — tested by using vertical half-decapitated root segments — is quite similar to the georeaction. This finding provides strong evidence that, in the case of Kelvedon maize roots, the inhibitory substance may depend on light. Observations related to the root segment of Anjou and Kelvedon maizes of which the tips are exchanged, are in agreement with the above results.     

Longitudinal and Transversal Microgradient of Acid Phosphomonoestherase in Growing and Geostimulated Maize Roots

A relatively simple and reproducible technique to analyse both longitudinal and transversal biochemical microgradients in roots has been presented. Although no statistically significant differences of acid phosphomonoestherase activity were found between upper and lower faces of geostimulated maize roots, an increase of activity was demonstrated in the two first mm of the horizontal roots in comparison with the vertical roots. These results were discussed in conection with the growth variation of these roots.     

Abscisic Acid Action on Basipetal Auxin Transport

Several experiments have been performed to analyse the ABA effects on the basipetal transport of IAA-2-¹⁴C, using sections of epicotyls prepared from etiolated Lens seedlings. The sections were incubated in an ABA solution or ABA was applied in the donor blocks containing IAA. For each type of assay, the uptake (analyses of the donor blocks) and the movement of IAA-C¹⁴ (analyses of the receiver blocks) were inhibited by ABA. The distribution of continuous decrease of the radioactivity, along the sections' axis, showed a ¹⁴C level from the apical towards the basal segments. ABA caused a decrease in the ¹⁴C concentration for the total sections, but a relative increase for the basal segment. When ABA was applied simultaneously with IAA in the donor blocks, the transport velocity of IAA, through the sections, was not changed significantly, while an ABA pretreatment caused a significant decrease.     

Dependence of B-A Conformational Change in DNA on Base Composition

IT is generally accepted that all native DNAs, irrespective of their origin, give essentially identical X-ray diffraction patterns characteristic of the A form at high humidities and of the A form at lower humidities^{1, 2}. The purpose of the work described here was an accurate characterization of B-A conformational changes in a range of DNA by infrared dichroism, which seems to be particularly appropriate for the structural characterization of nucleic acids^3–6 as a complement of X-ray diffraction. In previous infrared studies the A form and B-A conformational changes were not observed⁷.     

The Effect of Auxin and Abscisic Acid on the Catabolism of RNA

Abscisic acid (ABA) reduced growth in a root test (lentil),but the inhibition observed was less noticeable than that producedby using indol-3yl-acetic acid (IAA) alone. When both ABA andIAA were employed together, ABA acted as a growth-antagonistof IAA. ABA produced a strong inhibition of the total RNA accumulationand accelerated the RNase activity, while IAA strongly stimulatedthe RNA accumulation and greatly inhibited RNase activity. WhenABA and IAA were tested together, ABA also acted as an antagonistof TAA.