Robert M. Muir

Increase in Diffusible Auxin after Treatment with Gibberellin

When dwarf pea plants, normal pea plants, and sunflower plants were treated with gibberellin, they yielded 3, 2, and 10 times more auxin, respectively, than untreated plants.

Gibberellin: Effect on Diffusible Auxin in Fruit Development

Diffusible auxin is not present in tomato flowers at anthesis, but significant amounts can be obtained after the plants are treated with gibberellin. The early growth of the ovary in plants treated with gibberellin corresponds closely with growth after pollination and fertilization; the amounts of diffusible auxin are not significantly different over a period of 22 days.

Interaction of Methionine and Indoleacetic Acid in the Control of Abscission in Nicotiana.

Summary Methionine (presumably as a methyl donor) accelerates floral abscission in tobacco. IAA retards abscission. When the two factors are added to developing ovaries in combination, in general the effect is one of diminishing the effect of either when added alone. However, high concentrations of IAA completely overcome the accelerating effect of methionine.

Transport of Indoleacetic Acid in Pedicels of Tomato and Its Relation to Fruit Growth

Basipetal and acropetal transport of externally applied indoleacetic acid in the pedicels of tomato at different stages of development of the flower was examined. About one-fourth or one-fifth of the amount transported basipetally was transported acropetally after pollination and fertilization. Experimental evidence suggests that this acropetal movement results from a saturation of the transport system in the pedicel with auxin formed in the ovary following pollination and fertilization. Gibberellic acid has no direct effect on transport, either basipetal or acropetal. Indolebutyric acid is transported acropetally at all stages of flower development. The in vitro culture of excised ovaries with auxin in the medium involves an acropetal movement of auxin, and for the tomato this is a limiting condition. When larger amounts of IAA are provided by injection into the ovary, growth of the ovary is greater than when the auxin is provided in the medium. Auxin in the medium causes callus formation on the pedicel; this impairs movement of auxin and metabolites into the ovary, thus setting a limit for growth.

Mesocotyl growth of etiolated seedlings ofAvena sativa andZea mays in relation to light and diffusible auxin

Diffusible auxin levels were measured in coleoptiles and mesocotyls of dark-grown seedlings ofavena sativa (cv. Spear) andZea mays (cv. Golden Cross Bantam) using theAvena curvature bioassay. The coleoptile tip was confirmed as the major auxin source in etiolated seedlings. Auxin levels were found to decrease basipetally in sequent sections of theAvena coleoptile but not to decrease in apical sections of increasing length. An inhibitor capable of inducing positive curvatures ofAvena test coleoptiles was discovered in diffusates from the mesocotyls of oat and corn seedlings. The amount of this inhibitor was correlated with the cessation of mesocotyl growth of oat seedlings grown in darkness, and with the inhibition of mesocotyl growth of corn seedlings exposed to red light.

Effects of gibberellic acid and zeatin on the growth response of cucumber cotyledons

In contrast to cytokinin, gibberellic acid has no effect on the growth of the isolated cucumber cotyledon in darkness. Like cytokinins in light, gibberellic acid causes increases in fresh weight and area of the cotyledon at concentrations from 10−7 to 10−3 M. Radiant energies in the blue, red, and far-red regions of the spectrum all induce the growth responses to gibberellic acid. The effect of the far red is greater than that of the red, which is greater than that of the blue. Gibberellic acid is ineffective in the promotion of chlorophyll development, whereas cytokinins are very effective. Although zeatin and gibberellic acid both cause an increase in fresh weight and area of the cotyledons in light, they appear to have entirely separate actions in the growth responses.

Polarographic and Biologic Activities of N-Substituted Maleimides.

Summary The half-suppression values and half-wave potentials for 5 N-substituted maleimides were measured with the polarograph and compared with their inhibitory effects on growth of plant tissue induced by indoleacetic acid. The chemical group at the N-atom of the maleimide structure determines the ease of reduction of the carbon-carbon double bond. This chemical reactivity appears to be the basis for the biologic activity of maleimides with some possibility of adsorbability or surface activity playing a minor role.