RESUMEN
Previous studies showed that 3,5-diiodo-4-hydroxybenzoic acid (DIHB) promotes the root growth of cress seedlings (Lepidium sativum) in the light and also inhibits the production of ethylene by this tissue. Studies with structurally related phenolic acids suggest that there is an inverse correlation between these two effects.
RESUMEN
In previous research here, 3,5-diiodo-4-hydroxybenzoic acid (DIHB) was shown to promote the elongation of roots of cress (Lepidium sativum) seedlings growing in light, and to inhibit the auxin-induced production of ethylene in this tissue. Although DIHB is a cofactor for the oxidation of indole-3-acetic acid (IAA) by horse-radish peroxidase, it inhibits the decarboxylation of [1-(14)C]IAA by segments excised from cress roots. The inhibition by DIHB of ethylene production by this tissue does not, therefore, arise from a reduction of IAA levels. These findings are discussed in relation to the effects of DIHB on cress root growth.
RESUMEN
Exogeneous application of abscisic acid (ABA) to intact roots of LG 11 maize seedlings inhibits root elongation and induces bending of the root in response to gravity in darkness, even though the roots of these seedlings are not normally positively geotropic in the dark. ABA cannot, however, induce geotropic curvature in dark-exposed decapped roots, thus confirming that the root cap is the site of graviperception in the intact root.
RESUMEN
The effect of low concentrations of 3,5-diiodo-4-hydroxybenzoic acid (DIHB) in promoting the elongation of light-exposed cress (Lepidium sativum L.) roots has been further examined. Aeration of the DIHB solution in which the roots were grown largely removed the growth promotion. The addition of ethylene or the ethylene precursor methionine to the solution caused marked inhibition of root elongation and this effect was relieved by DIHB.
RESUMEN
3,5-Diiodo-4-hydroxybenzoic acid (DIHB) has been shown to exert an inhibitory effect on the formation of ethylene by the roots of intact cress Lepidium sativum seedlings in light, and by excised cress root segments. Adding IAA to the culture solution greatly promoted ethylene production, which was suppressed by DIHB. The findings together with results obtained with dinitrophenol (DNP), L-methionine and L-ethionine and also the horseradish peroxidase/methional system of Yang are discussed.The results indicate that the effect of DIHB in promoting the root growth of cress seedlings in nutrient solution in the light operates, at least in part, by suppressing the formation of the root growth inhibitor ethylene.
RESUMEN
Investigations into the relationship between the light-induced inhibition of root elongation and the response of Zea mays primary roots to gravity have revealed a close similarity between growth-inhibiting factor(s) produced in response to both stimuli. Evidence is presented that the inhibiting factor(s) produced in the root cap on exposure to white light can be used by the root to produce curvature in response to gravitational stimulation in darkness, i.e. under conditions in which dark exposed roots do not normally respond to gravity.The implications of these findings on the way in which roots respond to geotropic stimulation are discussed.
RESUMEN
Light-induced inhibition of the elongation of primary roots of Zea mays seedlings is dependent upon the perception of light by the root cap. Separate exposure of detached root caps and roots from which root caps have been removed (i.e. decapped roots) to white light or darkness has shown that the elongation of a dark-exposed root to which a light-exposed root cap is attached is inhibited significantly, whilst a light-exposed decapped root to which a dark-exposed root cap is attached is not inhibited. Thus the decapped root is not capable of perceiving the growth-inhibitory stimulus of white light and its rate of elongation is greater than that of light-exposed roots with root caps still intact. However, the capacity to perceive light and, therefore, to be inhibited by it, is restored to the decapped root approximately 5 h after removal of the root cap.Abscisic acid and two unidentified growth-inhibiting compounds are present in the root caps of light-grown but not of dark-grown Zea mays seedlings and a period of 2.5-3.0 h is required for transport of the compounds, in levels effective in growth inhibition, from the root cap into the apex of the root.
RESUMEN
Uninoculated roots of pea (Pisum sativum) and French bean (Phaseolus vulgaris) have been shown to exude a number of antifungal compounds when grown in a non-sterile aqueous aerated medium. These have been identified and their possible importance in relation to disease resistance is discussed.
