Flavonoids induced in cells undergoing nodule organogenesis in white clover are regulators of auxin breakdown by peroxidase.
It was tested whether flavonoids that specifically accumulate in cells undergoing early nodule organogenesis could affect auxin turnover by a peroxidase to explain local changes in auxin distribution that occur during nodule formation in white clover (Trifolium repens cv. Haifa). A fluorometric assay was developed to determine the kinetics of indoleacetic acid (IAA) breakdown rates by a horseradish peroxidase in vitro. Three flavonoid compounds, which had previously been localized and identified, were purified from root tissue and their tissue concentrations estimated. A derivative of 7,4'-dihydroxyflavone (DHF), as well as free DHF, strongly inhibited auxin breakdown by peroxidase at concentrations estimated in the root tissue. Formononetin, an isoflavonoid accumulating in nodule primordia, accelerated auxin breakdown by peroxidase at concentrations estimated to be present in the roots. These results suggest that local changes in flavonoid accumulation could regulate local auxin levels during nodule organogenesis. The results are consistent with previous observations on the localization of auxin during nodule organogenesis. A model for the interaction of flavonoids with peroxidases is proposed to explain changes auxin during nodule development. A similar mechanism could be involved in lateral root and root gall formation. (+info)
Leaf-atmosphere NH(3) exchange of white clover (Trifolium repens L.) in relation to mineral N nutrition and symbiotic N(2) fixation.
Plant-atmosphere NH(3) exchange was studied in white clover (Trifolium repens L. cv. Seminole) growing in nutrient solution containing 0 (N(2) based), 0.5 (low N) or 4.5 (high N) mM NO(3)(-). The aim was to show whether the NH(3) exchange potential is influenced by the proportion of N(2) fixation relative to NO(3)(-) supply. During the treatment, inhibition of N(2) fixation by NO(3)(-) was followed by in situ determination of total nitrogenase activity (TNA), and stomatal NH(3) compensation points (chi(NH(3))) were calculated on the basis of apoplastic NH4(+) concentration ([NH4(+)]) and pH. Whole-plant NH(3) exchange, transpiration and net CO(2) exchange were continuously recorded with a controlled cuvette system. Although shoot total N concentration increased with the level of mineral N application, tissue and apoplastic [NH4(+)] as well as chi(NH(3)) were equal in the three treatments. In NH(3)-free air, net NH(3) emission rates of <1 nmol m(-2) s(-1) were observed in both high-N and N(2)-based plants. When plants were supplied with air containing 40 nmol mol(-1) NH(3), the resulting net NH(3) uptake was higher in plants which acquired N exclusively from symbiotic N(2) fixation, compared to NO(3)(-) grown plants. The results indicate that symbiotic N(2) fixation and mineral N acquisition in white clover are balanced with respect to the NH4(+) pool leading to equal chi(NH(3)) in plants growing with or without NO(3)(-). At atmospheric NH(3) concentrations exceeding chi(NH(3)), the NH(3) uptake rate is controlled by the N demand of the plants. (+info)
Trifolium pratense (red clover) exhibits estrogenic effects in vivo in ovariectomized Sprague-Dawley rats.
Studies were conducted using an ovariectomized rat model to determine the estrogenic and antiestrogenic activity of Trifolium pratense L. (red clover) extracts. A red clover extract, standardized to contain 15% isoflavones was administered by gavage [250, 500 and 750 mg/(kg x d)] to virgin, ovariectomized 50-d-old Sprague-Dawley rats, for 21 d in the presence and absence of 17beta-estradiol [50 microg/(kg x d)]. Estrogenic effects included an increase in uterine weight, vaginal cell cornification and mammary gland duct branching. Red clover produced a dose-dependent increase in uterine weight and differentiated vaginal cells at the two higher doses, but it did not stimulate cell proliferation in the mammary glands. Neither antiestrogenic nor additive estrogenic properties were observed in any of the tissues studied. These data suggest that red clover extract is weakly estrogenic in the ovariectomized rat model. (+info)
The white clover enod40 gene family. Expression patterns of two types of genes indicate a role in vascular function.
Enod40 is one of the genes associated with legume nodule development and has a putative role in general plant organogenesis. We have isolated a small enod40 gene family from white clover (Trifolium repens), with three genes designated Trenod40-1, Trenod40-2, and Trenod40-3, all containing the conserved enod40 regions I and II. Trenod40-1 and Trenod40-2 share over 90% homology in the transcribed regions and high levels of similarity in their upstream regulatory sequences. Trenod40-1 and Trenod40-2 are similar to the enod40 genes of legumes forming indeterminate nodules (group II) and are predominantly expressed in nodules. Trenod40-3 shares only 32.8% identity with Trenod40-1 and Trenod40-2 within the transcribed region. Trenod40-3 is similar to the enod40 genes of legumes with determinate nodules (group I) and is not predominantly expressed in nodules. To our knowledge, this is the first report of both group I- and group II-type enod40 genes being expressed in a single legume species. In situ hybridization studies revealed that Trenod40 genes were highly expressed in non-symbiotic tissues, particularly in stolon nodes during nodal root and lateral shoot development. High levels of Trenod40 transcripts were also present in the vascular bundles of mature plant organs, mainly at sites of intensive lateral transport, suggesting a role in vascular tissue function. The expression pattern of Trenod40 genes was analyzed further using Trenod40 promoter-gus fusions in transgenic white clover and tobacco (Nicotiana tabacum), indicating that white clover and tobacco share the regulatory mechanisms for Trenod40-1/2 promoters and some aspects of Trenod40-3 regulation. (+info)
A simple model of feedback regulation for nitrate uptake and N2 fixation in contrasting phenotypes of white clover.
A simple three equation model is proposed for the feedback regulation of nitrate uptake and N2 fixation, based on the concentration of the organic N substrate pool within the plant and two parameters denoting the N substrate concentrations at which half-maximal inhibition occurs. This model simulated three contrasting phenotypes of white clover (Trifolium repens L.) inbred lines with (1) normal rates of nitrate uptake and N2 fixation (NNU); (2) low rates of nitrate uptake (LNU); and (3) very low rates of N2 fixation (VLF). The LNU phenotype was simulated by a decrease in the value of the inhibition parameter for nitrate uptake and the VLF phenotype was simulated by a decrease in the value of the N2 fixation inhibition parameter. The model was tested against nitrate uptake data obtained from white clover plants growing in flowing nutrient culture. There was an accurate prediction of the increase in nitrate uptake caused by N2 fixation activity of the NNU and LNU inbred lines being interrupted by a switch in gas phase from air to Ar : O2. The model was also tested against data for nitrate uptake, N2 fixation and %N from fixation for the three inbred clover lines grown in flowing nutrient culture at 0, 5 or 20 mmol m(-3) N(3-). Again there was accurate prediction of nitrate uptake, although simulated values for N2 fixation were more variable. The simple model has potential use as a sub-routine in larger models of legume growth under field conditions. (+info)
Morphological pattern of development affects the contribution of nitrogen reserves to regrowth of defoliated white clover (Trifolium repens L.).
The contribution of nitrogen reserves to regrowth following defoliation was studied in white clover plants (Trifolium repens cv. Huia). This was found to be closely linked to the morphological pattern of development of the aerial parts during the same period. Low temperature (6 degrees C) and short day exposure (8 h photoperiod) were used to induce dwarf development, i.e. to increase branching rate and to enhance new sites of leaf production during a period of regrowth. Treated plants exhibited a large reduction in leaf area and a large increase in leaf pool size for the first 10 d of a subsequent regrowth under standard culture conditions (16 h daylight; 22/18 degrees C day/night). The contribution of nitrogen from storage compounds in organs remaining after defoliation (sources) to regrowing tissues (sinks) was assessed by 15N pulse-chase labelling during regrowth following shoot removal. The mobilization of nitrogen reserves from storage tissues of regrowing clover was closely linked to the pattern of differentiation of the newly developed organs. It appeared that regrowth was supported less by endogenous N for the first 10 d after defoliation in treated plants, compared with control plants grown continuously in standard conditions. It is assumed that dwarf plants exhibit a lower dependence upon the mobilization of soluble proteins previously accumulated in roots and uncut stolons. The relationship between leaf development rate and N-uptake recovery following defoliation is discussed. (+info)
A developmentally based categorization of branching in Trifolium repens L.: influence of nodal roots.
This study describes the successive stages of development of branches from axillary buds in fully rooted plants of Trifolium repens grown in near optimal conditions, and the way in which this developmental pathway differs when nodal root formation is prevented as plants grow out from a rooted base. Cuttings of a single genotype were established in a glasshouse with nodal root systems on the two basal phytomers and grown on so that nodal rooting was either permitted (+R) or prevented (-R). In +R plants, axillary tissues could be assigned to one of four developmental categories: unemerged buds, emerged buds, unbranched lateral branches or secondarily branched lateral branches. In -R plants, branch development was retarded, with the retardation becoming increasingly pronounced as the number of -R phytomers on the primary stolon increased. Retarded elongation of the internodes of lateral shoots on -R plants resulted in the formation of a distinct fifth developmental category: short shoots (defined as branches with two or more leaves but with mean internode length equal to, or less than, 10% of that of the immediately proximal internode on the parent stolon) which had reduced phytomer appearance rates but retained the potential to develop into lateral branches. Transfer of +R plants to -R conditions, and vice versa, after 66 d demonstrated that subsequent branch development was wholly under the control of the youngest nodal root present, regardless of the age and number of root systems proximal to it. (+info)
Induction of apoptosis in low to moderate-grade human prostate carcinoma by red clover-derived dietary isoflavones.
Epidemiological evidence suggests a geographical basis for the incidence of prostate cancer and dietary factors, including isoflavone consumption, may be linked to this phenomenon. This paper reports a nonrandomized, nonblinded trial with historically matched controls from archival tissue designed to determine the effects of acute exposure to a dietary supplement of isoflavones in men with clinically significant prostate cancer before radical prostatectomy. Thirty-eight patients were recruited to the study upon diagnosis of prostate cancer. Before surgery, 20 men consumed 160 mg/day of red clover-derived dietary isoflavones, containing a mixture of genistein, daidzein, formononetin, and biochanin A. Serum PSA, testosterone, and biochemical factors were measured, and clinical and pathological parameters were recorded. The incidence of apoptosis in prostate tumor cells from radical prostatectomy specimens was compared between 18 treated and 18 untreated control tissues. There were no significant differences between pre- and posttreatment serum PSA, Gleason score, serum testosterone, or biochemical factors in the treated patients (P > 0.05). Apoptosis in radical prostatectomy specimens from treated patients was significantly higher than in control subjects (P = 0.0018), specifically in regions of low to moderate-grade cancer (Gleason grade 1-3). No adverse events related to the treatment were reported. This report suggests that dietary isoflavones may halt the progression of prostate cancer by inducing apoptosis in low to moderate-grade tumors, potentially contributing to the lower incidence of clinically significant disease in Asian men. The assessment of new prostatic therapies aimed at increasing apoptosis should control for intake of dietary isoflavones. (+info)