The effect of calcium (Ca²⁺) on Trifolium repens L. seedlings subjected to cadmium (Cd²⁺) stress was studied by investigating plant growth and changes in activity of antioxidative enzymes. ...Physiological analysis was carried out on seedlings cultured for 2 weeks on half-strength Hoagland medium with Cd²⁺ concentrations of 0, 400 and 600 μM, and on corresponding medium supplied with CaCl₂ (5 mM). Exposure to increasing Cd²⁺ reduced the fresh weight of the upper part (stems + leaves) of the seedlings more strongly than that of the root system. In both parts of T. repens seedlings H₂O₂ level and lipid peroxidation increased. In the upper part, Cd²⁺ exposure led to a significant decrease in the activity of superoxide dismutase, catalase and glutathione peroxidase and an increase in ascorbate peroxidase activity. In contrast, the roots showed an increase in the activity of antioxidative enzymes under Cd²⁺ stress. Ca²⁺ addition to medium reduced the Cd²⁺ accumulation, and considerably reversed the Cd²⁺-induced decrease in fresh mass as well as the changes in lipid peroxidation in the both parts of T. repens seedlings. Ca²⁺ application diminished the Cd²⁺ effect on the activity of antioxidative enzymes in the upper part, even though it did not significantly affect these enzymes in the roots. So the possible mechanisms for the action of Ca²⁺ in Cd²⁺ stress were considered to reduce Cd²⁺ accumulation, alleviate lipid peroxidation and promote activity of antioxidative enzymes.
Various nitric oxide (NO) regulators including the NO donor sodium nitroprusside (SNP), the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), the NO-synthase ...inhibitor
N
G
-nitro-
L
-Arg-methyl ester (
L
-NAME), and the SNP analogues sodium nitrite/nitrate and sodium ferrocyanide were investigated to elucidate the role of NO in white clover (
Trifolium repens
L.) plants after long-term (5 days) exposure to cadmium (Cd). A dose of 100 μM Cd stress significantly restrained plant growth and decreased the concentrations of chlorophyll and NO in vivo, whereas it disrupted the balance of stress-related hormones and enhanced the accumulation of Cd, thereby inducing reactive oxygen species (ROS) burst. However, the inhibition of plant growth was relieved by 50 μM SNP through its stimulation of ROS-scavenging compounds (ascorbic acid, ascorbate peroxidase, catalase, glutathione reductase, non-protein thiol, superoxide dismutase, and total glutathione), regulation of H
+
-ATPase activity of proton pumps, and increasing jasmonic acid and proline but decreasing ethylene in plant tissues. Even so, the alleviating effect of SNP on plant growth was counteracted by cPTIO and
L
-NAME and was not observed with SNP analogues, suggesting that the protective roles of SNP are related to the induction of NO. These results suggest that NO may improve the Cd tolerance of white clover plants by eliminating oxidative damage, re-establishing ATPase activity, and maintaining hormone equilibrium. Improving our understanding of the role of NO in white clover plants is key to expanding the plantations to various regions and the recovery of pasture species in the future.
Optimum plant densities are a key to maximise yields in most crops. However, such information is often lacking for more environmentally sound cropping systems, such as living mulches (LM) for small ...grains. In 2004 and 2005, three trials were conducted in the Swiss Midlands on fields managed in accordance with the Swiss organic farming guidelines. The objective of the study was to determine whether seeding density of winter wheat (
Triticum aestivum L.) is a relevant factor for determining grain yield in a white clover (
Trifolium repens L.) living mulch. The winter wheat cv. Titlis was directly sown in wide spaced rows (0.375
m) at densities of 300 (LM300), 450 (LM450) or 600 (LM600) viable grains m
−2 in a white clover living mulch established at a seeding rate of 15
kg
ha
−1. A bare soil control treatment with a wheat density of 450 viable grains m
−2 (BS450) was also included in the trials. Mean grain yields of LM300, LM450, and LM600 never reached the values observed in BS450. This was mainly due to a lower ear density, which, nevertheless, increased linearly with the seeding density within the living mulch in all trials, but the rate of increase depended on the environment. The decrease of the grain weight brought about by the increasing seeding density had only a marginal impact on the grain yield, which was increased from 1.31, 1.98, and 4.09
Mg
ha
−1 (LM300) to 1.97, 2.64, and 4.75
Mg
ha
−1 (LM600) for each of the three trials in the study. Significantly higher protein contents were observed for LM300 compared to the higher densities in the living mulch and to BS450. Our research showed that an increase of the seeding density is an effective mean to increase the grain yield in living mulch systems with white clover. However, it is likely that the control of the living mulch to reduce competition with the main crop is a more relevant factor.
Antioxidant response to drought in red (Trifolium pratense L., cv. “Start”) and white clover (Trifolium repens L, cv. “Haifa” and cv. “Debut”) grown as soil cultures was evaluated in water-deprived ...and recovered plants. Drought provoked oxidative stress in leaves confirmed by the considerable changes in electrolyte leakage, malondialdehyde, hydrogen peroxides and proline contents. Immunoblot of Δ-1-pyrroline-5-carboxylate synthetase (P5CS), which catalyzes the first two steps in proline biosynthesis, revealed strong induction of the enzyme in red clover plants submitted to drought. Water-deprived white clover plants exhibited distinct P5CS profiles. This was related to different drought tolerance of the studied T. repens cultivars. Isoenzyme analyses of superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) demonstrated certain differences in antioxidant defence among the tested varieties. It was confirmed that MnSOD (in both T. repens and T pratense) and FeSOD (in T. repens) isoforms were the most affected by drought. The red clover cultivar “Start” exhibited the lowest FeSOD and POX activities which could contribute to its poor performance under water deprivation.
Four breeding lines (BLs) of white clover, which range in terms of their disposition to increase biomass in response to low or high phosphate (P) levels in soil, were evaluated further when grown ...hydroponically. BL 45 increased both fresh and dry weight in response to P-deprivation, while BL 49 displayed the same significant stimulation in response to sufficient P. However, when compared these lines did not accumulate any significantly higher levels of P, and all four lines showed the same changes to root:shoot ratio in response to P-deprivation, as well as the induction of both soluble and cell-wall-associated acid phosphatase activity. These results confirm that there is no direct relationship between growth (as an increase in biomass) and acid phosphatase activity and further some responses to P-deprivation may be common to all genetic backgrounds suggesting that they are not part of the intricate mechanisms governing these responses.
White clover (Trifolium repens L.) is one of the most important legumes for fodder production in temperate climates, particularly in intensive pasture systems. Like many other forage legumes, it ...lacks the energy content to maximize productivity of modern ruminant livestock breeds. White clover produces water-soluble carbohydrates and starch in its leaves as a diurnal product of photosynthesis. However, little is known about the genetically encoded variability of diel changes in carbohydrate content. We assessed the amount of glucose, fructose, sucrose, and starch in the leaves of 185 plants of a genetically diverse white clover population. Water-soluble carbohydrates only provided on average 10.6% of dry weight (DW) of the total analyzed non-structural carbohydrate (NSC) content at the end of the day (ED), while starch supplied 89.4% of the NSC content. The top 5% of individuals accumulated over 25% of their DW as starch at ED. The leaf starch content at ED showed up to a threefold difference between genotypes, with a repeatability value of 0.95. Our experiments illustrate both the physical potential of white clover to serve as a competitive energy source to meet the demand of modern ruminant livestock production and the genetic potential to improve this trait by breeding.
The influence of P-supply on root system architecture (primary root length, number and total length of lateral roots) through the effects of ethylene (ACC) and auxin 1-naphthylacetic acid (NAA) has ...been examined in the legume white clover (
Trifolium repens
L.). Higher concentrations (1 and 10 μM) of ACC and NAA (100 nM) inhibited growth, while lower concentrations (100 nM ACC, 5 nM NAA) either had no effect or stimulated growth in P-sufficient (1 mM Pi) roots. In response to low (10 μM) P, a stimulation of primary root growth, number of lateral roots and mean length of lateral roots was observed, while a super-stimulation of these growth parameters occurred in response to subsequent 100 nM ACC treatment suggesting that the low P treatment increased the sensitivity of the roots to ethylene. Examination of the primary roots of
DR5p::GUS
transformants suggests that this change in sensitivity induced by low P occurs through the promotion of auxin signalling/transport to the root apex. These results are discussed in terms of the role of ethylene and the significance of changes in sensitivity to the hormone in modulating root system architecture in response to low P-supply.
To elucidate the effect of selenium (Se) on the ascorbate–glutathione (ASC–GSH) cycle under drought stress, the activities of antioxidant enzymes and the levels of molecules involved in ASC–GSH ...metabolism were studied in Trifolium repens seedlings subjected to polyethylene glycol (PEG)-induced water deficit alone or combined with 5 μM Na2SeO4. Compared to the control, H2O2, thiobarbituric acid reactive substances (TBARS), ascorbate (ASC), dehydroascorbate (DHA), and glutathione disulfide (GSSG) contents increased, whereas a constant content of glutathione (GSH) and decreases in ASC/DHA and GSH/GSSG ratios were observed in the presence of PEG. The activities of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were upregulated, except for monodehydroascorbate reductase (MDHAR) activity during PEG-induced water deficit. Se application decreased the contents of H2O2, TBARS, DHA, and GSSG, increased the levels of GSH and ASC, and inhibited the decreases of ASC/DHA and GSH/GSSG ratios. Although it did not affect APX activity significantly, Se addition improved the activities of MDHAR, DHAR, and GR. Furthermore, GR activity showed the highest increase followed by that of DHAR and MDHAR in decreasing order. These data indicated that fluctuations in ASC–GSH metabolism resulting from Se may have a positive effect on drought stress mitigation, and the regulation in the ASC–GSH cycle can be attributed mainly to GR and DHAR in PEG + Se-treated T. repens seedlings.
The objective of this work was to construct a model of aerial development of clover that takes into account morphogenetic responses to the light environment, and to use it to analyse and understand ...these processes in terms of signal perception and integration. The plant model was interfaced with a Monte Carlo model that determines photosynthetically active radiation (PAR) and red/far-red ratio (R/FR) throughout the canopy, taking into account the absorption, reflection and transmission of light by individual leaves. Light intensity and quality were sensed by the plant model at discrete time intervals and at discrete sites of perception: apices, emerging internodes and petiole tips. This input regulated the final size of internodes and leaves, the vertical positioning of leaves, and the branching delay. The empirical relations (regression functions) quantifying this regulation were derived from data reported in the literature and original measurements. Simulations produced realistic visualizations and quantitative characterizations of the modelled plants for different light treatments. These results were in general agreement with observations of real plants growing under similar conditions, suggesting that the dependence of organ size and position on light treatments can be regarded as an integration of the responses of individual plant organs to their local light environment. The model is used to describe the regulation of branch appearance and the impact of self-shading on plant morphogenesis as a function of local light environment.
Predicting species composition in mixed swards by near infrared reflectance spectroscopy (NIRS) can save labour in grassland research, provided equations are available. This study compares ...calibration strategies to predict species composition in swards with tall fescue (Festuca arundinacea), perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The compared calibration strategies were based on either real or artificial samples. Real samples are samples taken from multispecies swards; the species composition is known by hand separating; after separating, the original samples are recomposed. Artificial samples are samples obtained by mixing single species grown in pure stands in known proportions. The performance of the equation based on real samples was significantly better than the performance of the equation based on artificial samples. We hypothesized that the weak performance of the equation based on artificial samples was due to a lack of environmental variation in the spectra of the artificial samples. The hypothesis was supported by the good performance of a novel calibration strategy based on the spectra of the artificial samples with added variation. According to the obtained results, a calibration strategy based on few but diverse calibration samples is discussed.
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