Visible Toxicity Symptoms Research Articles

Copper uptake by four Elsholtzia ecotypes supplied with varying levels of copper in solution culture

The effects of copper (Cu) on the yield and Cu uptake of three ecotypes of Elsholtzia splendens and one of Elsholtzia argyi were studied using solution culture. Three Cu concentrations were compared: 0.31 (control), 50 and 100 μmol L − 1. Although E. argyi took up more Cu in the aboveground parts, typical visual symptoms of Cu toxicity appeared when the plants grew in 50 and 100 μmol Cu L − 1. In contrast, plants from all three populations of E. splendens showed high Cu tolerance and substantial shoot Cu accumulation of 58–144 mg kg − 1. Shoot Cu concentrations were about 16–27 times higher than root Cu concentrations. Root-to-shoot ratio of the E. argyi ecotype was halved when Cu was supplied at a level of 100 mg L − 1 compared to the control (0.31 mg L − 1) but the ratio increased by 6–47% in the three E. splendens ecotypes. The increase in root-to-shoot ratio in E. splendens may be a mechanism by which the plants can tolerate high Cu concentrations. There were few differences in morphology among the three E. splendens ecotypes in response to added Cu. The results are discussed in relation to the possible use of E. splendens as a pioneer species in the phytostabilization of Cu-contaminated soils.

Deterioration of Fruit Quality of Tomato by Excess Cobalt and Its Amelioration

Tomato (Lycopersicon esculentum L.) cv. Alivikas was grown in refined sand at two levels of phosphorus (P): 1.5 mM (adequate) and 3.0 mM (high); 0.5 mM cobalt (Co) was supplied at each P level after 35 days of growth. Visible symptoms of Co toxicity appeared as interveinal chlorosis of young leaves after 8 days of metal supply. Biomass was depressed at both P levels with excess Co, although less at the high P level. Discontinuation of high P or Co or additional iron (Fe) supply also increased the biomass. The fresh weight of fruits was decreased, but dry weight was increased in high P supply. Quality of fruits was poor with Co‐treated plants as Co depressed the fruit fresh weight and dry weight, volume and size of fruits, concentrations of chlorophyll a, b and carotene, ascorbic acid, lycopene, reducing sugars, and starch, and increased acidity and phenols. These effects were greater with adequate vs. high P. High P (without Co) improved fruit quality by increasing fruit dry weight, volume, and size of fruits, ascorbic acid content, and reducing sugars and by decreasing acidity. Accumulation of cobalt in leaves and fruits was greater, and these plant parts developed visible Co toxicity symptoms. Fruits developed black patches with prolonged Co supply. New fruits developed after the discontinuation of the Co supply appeared green and normal, but were few in number compared with increased vegetative growth of plants (cobalt supplied with the normal level of phosphorus). Earlier flowering, fruiting, and ripening were observed in plants with high phosphorus rather than adequate P. Brown spots in fruits developed after 18–20 days of Co supply, and in the most severe case, young emerging fruits were totally brown. Amelioration of cobalt toxicity was better with discontinuation of Co than withdrawal of high P with additional Fe.

Soybean Genotypic Difference in Growth, Nutrient Accumulation and Ultrastructure in Response to Manganese and Iron Supply in Solution Culture

The objective of this research was to characterize the physiology and cell ultrastructure of two soybean genotypes subjected to nutrient solutions with increasing concentrations of manganese (Mn) at two contrasting iron (Fe) concentrations. Genotypes 'PI227557' and 'Biloxi' were selected based on their distinctly different capacities to accumulate Mn and Fe. * Bradyrhizobium-inoculated plants were grown in hydroponic cultures in a greenhouse. Nutrient solutions were supplied with Mn concentrations ranging from 0.3 to 90 microm, at either 5 or 150 microm Fe as FeEDTA. * For both genotypes and at both Fe concentrations, Mn concentrations from 6.6 to 50 microm did not affect shoot, root and nodule mass, or leaf and nodule ureide concentration. Mn concentrations of 70 and 90 microm did not result in visible toxicity symptoms, but hindered growth and nodulation of 'Biloxi'. An Mn concentration of 0.3 microm was, however, deleterious to growth and nodulation for both genotypes, and caused an accumulation of ureides in leaves and major alterations in the ultrastructure of chloroplasts, nuclei and mitochondria, regardless of the Fe concentration. In 'PI227557', there was also a proliferation of Golgi apparatus and endoplasmic reticulum in the cytoplasm of leaf cells, and nodules showed disrupted symbiosomes lacking poly-beta-hydroxybutirate grains concomitantly with a proliferation of endoplasmic reticulum as well as arrested bacterial division. At 15 microm Fe, ferritin-like crystals were formed in the lumen of chloroplasts of 'PI227557' plants. For both genotypes, there was an antagonism between the Fe and Mn concentrations in leaves, the higher values of both microelements being detected in 'PI227557'. The absence of any detectable relationship between Fe or Mn and zinc, phosphorus and copper concentrations in leaves ruled out those micronutrients as relevant for Mn and Fe nutrition in soybeans. * The results confirmed the greater capacity of 'PI227557' for Mn and Fe accumulation than 'Biloxi' for most nutrient treatments. Hence, 'PI227557' may be a very useful genetic resource both in developing soybean cultivars for growth on low nutrient soils and in physiological studies to understand differing approaches to nutrient accumulation in plants.

UPTAKE AND DISTRIBUTION OF SELENIUM IN DIFFERENT FERN SPECIES

There has been an interest in using hyperaccumulating plants for the removal of heavy metals and metalloids. High selenium (Se) concentrations in the environment are detrimental to animals, humans, and sustainable agriculture, yet selenium is also an essential nutrient for humans. This experiment was conducted to screen fern plants for their potential to accumulate selenium. Eleven fern species, Pteris vittata, P. quadriaurita, P. dentata, P. ensiformis, P. cretica, Dryopteris erythrosora, Didymochlaena truncatula, Adiantum hispidulum, Actiniopteris radiata, Davallia griffithiana, and Cyrtomium fulcatum, were grown under hydroponic conditions for one week at 20 mg L− 1 selenate or selenite. Root Se concentrations reached 245–731 and 516–1082 mg kg− 1 when treated with selenate and selenite, respectively. The corresponding numbers in the fronds were 153–745 and 74-1,028 mg kg− 1 with no visible toxicity symptoms. Only three fern species were able to accumulate more Se in the fronds than the roots, which were D. griffithiana when treated with selenate, P. vittata when treated with selenite, andA. radiata regardless of the forms of Se. A. radiata was the best species overall for Se accumulation. More research is needed to further determine the potential of the fern species identified in this study for phytoremediation of the Se contaminated soils and water.

Shoot Cadmium Accumulation and Photosynthetic Performance of Barley Plants Exposed to High Cadmium Treatments

Barley (Hordeum vulgare L., cv. Ribeka) plants grown in sand culture were exposed for 10 days to high cadmium (Cd) treatments in order to study both shoot Cd accumulation and photosynthetic performance. Cadmium inhibited root dry mass and induced changes in biomass allocation pattern without any effect on biomass accumulation at the whole plant level. The maximal shoot Cd concentration—41 ± 8 mg Cd kg−1 DW—without any visual toxicity symptoms on the shoots was found at 28 mg Cd kg−1 sand. Reduced leaf gas exchange, photosynthetic pigments content and electron transport activity but not altered lipid peroxidation status of thylakoids was, however, detected at the highest treatment—42 mg Cd kg−1 sand. The results indicated good tolerance of barley growth and photosynthetic machinery to Cd, but the shoot Cd accumulation achieved even in the artificial conditions was considered insufficient for short-term phytoextraction.

Effect of chloride in irrigation water and form of nitrogen fertilizer on Virginia (flue-cured) tobacco

One of the main sources of considerable amounts of chloride to soils is irrigation water. The responses of tobacco ( Nicotiana tabacum L.) to chloride are varied and inconsistent depending on the tobacco type, variety and methods of fertilization, cultivation and harvesting used. In this work, the impact of the interaction between four chloride levels (10, 20, 40, 80 mg L −1) in irrigation water and three nitrogen fertilizer forms (NO 3–N 100%, NH 4–N 100% and NO 3–N 50%:NH 4–N 50%) on growth, agronomic and chemical characteristics of Virginia tobacco was evaluated over 2 years (1999, 2000) in an outdoor pot experiment. The results showed that the adverse influence of chloride in irrigation water on plant height and number of leaves per plant was already substantial above 40 mg L −1, within 30 days after transplanting. In this period, visual toxicity symptoms of chloride appeared on the lower leaves of plants treated with ammonium nitrogen. In addition, the effect of chloride on flowering time, chlorophyll content of leaves, aboveground fresh weight of plant, total cured product yield and chemical characteristics, depended on the form of nitrogen, with nitrate nitrogen restricting the detrimental effects of chloride in irrigation water up to 40 mg L −1. The reduced yield of cured product at 80 mg L −1 was the result of the adverse effects of chloride on the leaves of the middle and upper stalk position. Leaf chloride concentration was highest in the upper leaves and increased linearly with the increase of chloride level in irrigation water at each leaf position on the stalk and this increase was more rapid as ammonium nitrogen percentage was increased. Chloride increased the concentration of reducing sugars in cured leaves at each leaf position, in all nitrogen forms and nicotine mainly in plants treated with nitrate nitrogen. The changes in total nitrogen and ash content are considered as minimal. We conclude that the optimum chloride level in irrigation water is below 20 mg L −1, whereas the level of 40 mg L −1 in combination with nitrate nitrogen fertilizers can be considered as the upper threshold to avoid adverse effects on Virginia tobacco.

A critical analysis of the causes of boron toxicity in plants

ABSTRACTThis study investigated the main factors contributing to boron toxicity in plants. Growth was rapidly inhibited by internal B concentrations in the range 1–5 m m across a range of plant types that included monocot, dicot and algal species. In contrast, mature cells were able to withstand up to 60 m m B for several days. In wheat, rapid inhibition of root growth occurred if high B was applied to the root tip, but not if high B was applied to mature sections of the root. In leaves, there were gradations in B concentrations that correlated with visible symptoms of toxicity. However, there was no evidence to support the hypothesis that toxicity in leaves is due to osmotic stress induced by the accumulation of B. Analysis of the sensitivity to B of a range of metabolic processes including photosynthesis, respiration and protein synthesis leads to the conclusion that growth is not restricted by effects of B on energy supply and not directly by inhibition of protein synthesis. At higher B concentrations, many cellular activities were found to be partially inhibited and the toxicity to mature tissues was therefore considered not to arise from the disruption of a single process, but from the accumulated retardation of many cellular processes, exacerbated in light by photo‐oxidative stress.

Cadmium tolerance in Thlaspi caerulescens: I. Growth parameters, metal accumulation and phytochelatin synthesis in response to cadmium

A population of the metallophyte, Thlaspi caerulescens, originating from a Cd–Pb–Zn old mining and smelter site at Plombières (Belgium) was studied. T. caerulescens was cultivated hydroponically to investigate Cd uptake and tolerance. Cd was added to Hoagland’s medium at concentration range from 5 to 500 μM. The plants could tolerate 500 μM Cd in the solution showing only minor visible symptoms of toxicity but with a 32% decrease in fresh weight. After 14 days at 500 μM, Cd content in roots and shoots was 707 and 602 mg kg −1 of dry weight (d.w.), respectively. Application of Cd to hydroponically cultivated T. caerulescens induced the accumulation of PCs in plant roots and shoots. Buthionine sulfoximine (BSO) application almost completely reduced (by 98–100%) the accumulation of PCs without simultaneous increase in plants sensitivity to Cd. These results suggest a minor if any role of PCs in tolerance to Cd of the studied population of T. caerulescens in hydroponics. On the other hand, no PC accumulation was detected either in T. caerulescens plants growing in their natural environment at Plombierès or in plants growing in their native soil in a greenhouse. These results suggest that naturally selected tolerance in T. caerulescens population from Plombières is not associated with enhanced PCs synthesis.

Cadmium tolerance in Thlaspi caerulescensI. Growth parameters, metal accumulation and phytochelatin synthesis in response to cadmium

A population of the metallophyte, Thlaspi caerulescens , originating from a Cd–Pb–Zn old mining and smelter site at Plombières (Belgium) was studied. T. caerulescens was cultivated hydroponically to investigate Cd uptake and tolerance. Cd was added to Hoagland’s medium at concentration range from 5 to 500 μM. The plants could tolerate 500 μM Cd in the solution showing only minor visible symptoms of toxicity but with a 32% decrease in fresh weight. After 14 days at 500 μM, Cd content in roots and shoots was 707 and 602 mg kg −1 of dry weight (d.w.), respectively. Application of Cd to hydroponically cultivated T. caerulescens induced the accumulation of PCs in plant roots and shoots. Buthionine sulfoximine (BSO) application almost completely reduced (by 98–100%) the accumulation of PCs without simultaneous increase in plants sensitivity to Cd. These results suggest a minor if any role of PCs in tolerance to Cd of the studied population of T. caerulescens in hydroponics. On the other hand, no PC accumulation was detected either in T. caerulescens plants growing in their natural environment at Plombierès or in plants growing in their native soil in a greenhouse. These results suggest that naturally selected tolerance in T. caerulescens population from Plombières is not associated with enhanced PCs synthesis.

Phytotoxicity of Several Iron Fertilizers and Their Effects on Fe, Mn, Zn, Cu, and P content of African Marigolds and Zonal Geraniums

Zonal geraniums (Pelargonium ×hortorum) from seed and african marigolds (Tagetes erecta), which are known to be highly susceptible to Fe toxicity problems, were grown with I, 2, 4, or 6 mm Fe from ferrous sulfate, ferric citrate, FeEDTA, FeDTPA, FeEDDHA, ferric glucoheptonate, or ferrous ammonium sulfate in the subirrigation solution. FeEDTA and FeDTPA were highly toxic to both species, even at the 1 mm rate. Ferrous sulfate and ferrous ammonium sulfate caused no visible toxicity symptoms on marigolds, but did reduce dry weights with increasing Fe concentrations. Both materials were slightly to moderately toxic on zonal geraniums. FeEDDHA was only mildly toxic at the 1 mm concentration on both species, but was moderately toxic at the 2 and 4 mm concentrations. Substrate pH was generally negatively correlated with geranium dry weight and visible phytotoxicity ratings, with the least toxic materials, ferrous sulfate and ferrous ammonium sulfate, resulting in the lowest substrate pHs and the chelates FeEDTA, FeDTPA, and FeEDDHA the highest pH. The ionic Fe sources, ferrous sulfate and ferrous ammonium sulfate, suppressed P uptake in both species, whereas the Fe chelates did not. Fe EDDHA should be considered as an effective and less toxic alternative for the widely used FeEDTA and FeDTPA in the production of these crops.

Influence of organic matter on the uptake of cadmium, zinc, copper and iron by sorghum plants

This article describes an experiment, carried out under controlled environment conditions, to investigate the effects of a fulvic acid fraction of soil organic matter on growth, cadmium (Cd) uptake and redistribution by sorghum. In addition the uptake of copper (Cu), zinc (Zn) and iron (Fe) was also determined. Sorghum was grown in nutrient solutions with 0, 0.1, 1 and 10 mg Cd dm −3, in the absence and presence of organic matter (32 mg C dm −3), for various periods up to 20 days. A decrease in sorghum biomass due to Cd toxicity was observed at 10 mg Cd dm −3, but for concentrations of 0.1 and 1 mg Cd dm −3 the biomass was increased compared with control, without visual toxicity symptoms. The presence of organic matter (OM) further increased biomass production. Cadmium was mainly retained in sorghum roots, as usually found in tolerant plants, but Cd accumulation in sorghum was greater than in other Gramineae, or even more tolerant plants such as lettuce. The presence of OM decreased the bioavailability of Cd that was partially retained in solution by the OM ligands. However, OM promoted the translocation of Cd to shoots, an effect that may pose a risk to public health because plant-animal transfer of Cd could be enhanced. The presence of OM decreased the uptake of Cu, Zn and Fe. The presence (vs. absence) of 0.1 mg Cd dm −3 enhanced the uptake of Fe, both in the absence and presence of OM.

Iron distribution in three central Amazon tree species from whitewater-inundation areas (várzea) subjected to different iron regimes

Trees inhabiting central Amazon floodplain forests are subjected to an annual flood-pulse lasting up to 10 months, leading to both oxygen shortage and accumulation of high levels of reduced iron. To understand the mechanisms underlying the adaptation to these conditions, cuttings from three tree species typical of varzea inundation forests (Salix martiana, Tabernaemontana juruana, and Laetia corymbulosa), were cultivated either aerobically or anaerobically under different iron regimes in greenhouse experiments. Although all species are considered to be non-deciduous, Laetia corymbulosa lost and formed new leaves continuously during the experimental period. Although relative growth rates (RGRs) of all species declined in response to hypoxic conditions, no marked changes in RGRs were apparent among different iron concentrations in the growth medium, ranging from 50 to 500 µM, supplied in ferrous form as FeSO4. Whereas roots exhibited color changes due to the formation of iron precipitates, no visual symptoms of iron toxicity were observed in the leaves. Iron concentration increased in all organs of all species with increasing iron concentrations in the medium, except for leaves of S. martiana and T. juruana, suggesting an effective restriction of iron influx into the leaf symplast. Although the leaf iron concentration was at the upper limit of the critical range at high external iron levels, it is suggested that internal active transport rather than intracellular detoxification mechanisms contribute to the tolerance to supra-optimal iron levels. Anatomical traits such as suberization of peripheral cell walls and the formation of aerenchyma appear to be of minor importance for Fe tolerance.

Zinc Concentration in Hydroponic Solution Culture Influences Zinc and Sulfur Accumulation in Brassica rapa L

A rapid cycling population of Brassica rapa L. was grown hydroponically and subjected to solution zinc (Zn) concentrations ranging from 0.05 to 200 mg L−1. The objectives of the study were to determine how available Zn affected plant growth, and the accumulation of Zn, total sulfur (S), sulfate (SO4 2−) in B. rapa shoots. Plants exposed to Zn levels above 5 mg L−1 exhibited mild visual toxicity symptoms as well as stunted root and shoot growth. Plants exposed to Zn levels ≥50 mg L−1 had chronic toxicity symptoms after several days of exposure and did not measurably grow. Mineral analysis showed that Zn accumulated linearly in plant shoots in response to increasing Zn, despite the expression of varying levels of Zn toxicity symptoms. Total shoot S and SO4 2− accumulated at amounts greater than the control when exposed to Zn levels ≥25 mg L−1 Zn; even though solution S did not vary among treatments. At the higher Zn concentrations, shoot S did not differ from the control. Additionally, SO4 2− was responsible for the nearly all the S measured regardless of Zn exposure. This suggests that Zn uptake and accumulation differs from S when exposed to increasing Zn availability.

Cádmio em Latossolo Vermelho cultivado com milho em colunas: mobilidade e biodisponibilidade

Com vistas em avaliar a dinâmica do cádmio no sistema solo-planta, instalou-se um experimento em colunas de PVC (0,10 m de diâmetro e 0,80 m de altura), preenchidas com amostras de Latossolo Vermelho distrófico típico com 320 g kg-1 de argila (elevou-se V % a 70) onde se aplicou biossólido (pH 6) contaminado com Cd, incorporado na camada de 0-0,2 m da coluna. Os tratamentos com biossólido contaminado com cádmio foram (mg kg-1): 0 (testemunha), 2.500 e 5.000 de Cd e dois adicionais (2.500 Cd + 2.500 Pb e 5.000 Cd + 5.000 Pb). Cultivou-se milho nas colunas por um período de 80 dias. As concentrações de Cd nas amostras de solo e na parte aérea do milho foram determinadas em extrato nitro-perclórico. A alta concentração do Cd no solo restringiu-se apenas à camada de incorporação, não havendo lixiviação do elemento na coluna do solo. A concentração de 12 mg kg-1 de Cd não foi suficiente para provocar sintomas visuais de fitotoxidez de Cd em milho. O Pb adicionado juntamente com o Cd não apresentou interferência no sistema solo-planta.

Aplicações de fertilizantes foliares na nutrição e na produção do pimentão e do tomateiro

Avaliou-se a eficiência de fertilizantes foliares, contendo Ca e B, na nutrição e produção do pimentão cv. Mayata e do tomate cv. Carmem, cultivados em estufas. O delineamento experimental foi de blocos ao acaso com seis tratamentos, três e quatro repetições, respectivamente, para o tomateiro e pimentão. Os tratamentos foram a água de retortagem de xisto (100; 78; 3,0; 12,5; 3,0; 12,5; 4,0 e 0,2 g.L-1 de N, K, S, Ca, Mg, B, Mn e Mo, respectivamente) a 0,1; 0,25; 0,5 e 1%; os sais ácido bórico (170 g.kg-1 de B) a 0,15% mais cloreto de cálcio a 0,15% e o quelato de cálcio (200 g.kg-1 de Ca) a 0,1% e boro orgânico (10 g.kg-1 de B) a 0,15%. A aplicação de água de retortagem de xisto a 0,5% via foliar aumentou em 27,4% a produção de frutos de pimentão e os teores foliares de Mg e S em relação à aplicação desse fertilizante a 0,1%. Para o tomateiro, as pulverizações com água de retortagem de xisto a 0,5 e 1% elevaram em 60,5 e 93,8% a produção de frutos em comparação à menor dose desse fertilizante. Os maiores teores de B nas folhas de pimentão e de tomate foram obtidos com as aplicações de sais e resultaram em sintomas visuais de toxicidade de B no início do desenvolvimento das culturas.

Effect of heavy metals Co 2+, Ni 2+ and Cd 2+ on growth and metabolism of cabbage

Exposure of cabbage plants to excess (500 μM) of Co 2+, Ni 2+ and Cd 2+ in sand culture led to increased accumulation of the metals, inhibition of growth and induction of visible symptoms of metal toxicity. In addition to chlorosis, Co 2+ treated plants exhibited reddish purple coloration along leaf margins, Ni 2+ treated plants exhibited black spots near leaf margins, and Cd 2+ treated plants developed purple coloration along leaf margins. At equimolar concentration, inhibition of growth was most severe with excess Cd 2+ and induction of visible symptoms was most severe with excess Ni 2+. Exposure to excess concentration of the heavy metals decreased the uptake of Fe and its translocation to leaves. Exposure to each Co 2+, Ni 2+ and Cd 2+ decreased chlorophyll content (Ni 2+>Cd 2+>Co 2+), concomitant with decrease in the activities of the Fe enzymes—catalase and peroxidase, suggesting reduced availability of Fe for chlorophyll–heme biosynthesis. Each Co 2+, Ni 2+ and Cd 2+ decreased water potential and transpiration rate, associated with increase in diffusive resistance showing development of water stress. This was further substantiated by enhanced accumulation of proline in the leaves of plants exposed to Co 2+, Ni 2+ and Cd 2+.

Ethanol sensitivity of rice and oat coleoptiles.

The ability to avoid the ethanol-induced injury was evaluated in rice (Oryza sativa L.) and oat (Avena sativa L.) coleoptiles. The growth of the rice and oat coleoptiles was inhibited by ethanol exogenously applied at concentrations greater than 200 and 30 mM, respectively. At 300 mM ethanol, oat coleoptiles were brown and flaccid but rice coleoptiles did not show any visible symptoms of toxicity. The acetaldehyde level in rice and oat coleoptiles was increased by exogenously applied ethanol and the increases were greater in oat than in rice coleoptiles under aerobic and anaerobic conditions. At 300 mM ethanol, the acetaldehyde concentrations in the rice and oat coleoptiles were 46 and 87 nmol g-1 FW under aerobic conditions, respectively, and 52 and 124 nmol g-1 FW under anaerobic conditions, respectively. The activity of alcohol dehydrogenase (ADH; EC 1.1.1.1) in the direction of ethanol to acetaldehyde was greater in oat than in rice coleoptiles and ADH protein in oat coleoptiles was more induced by exogenously applied ethanol than that in rice coleoptiles. These results suggest that in vivo conversion rate of ethanol to acetaldehyde by ADH is lower in rice than oat coleoptiles, which may be one of the reasons that ethanol sensitivity of rice is much lower than that of oat coleoptiles. The great ability of rice to avoid the ethanol-induced injuries may contribute its anoxia tolerance when glycolysis and ethanolic fermentation replace the Krebs cycle as the main source of energy under anaerobic conditions.

Field activities and blood profile of pregnant South African indigenous goats after receiving dihydroxy pyridone-degrading rumen bacteria and grazing Leucaena leucocephala-grass or natural pastures

Twenty-four multiparous female South African indigenous goats were used. Once a week during the 2nd (weeks 8, 11 and 14) and 3rd (weeks 18, 19 and 20) trimesters, between 08·00 and 15·00 h, four females per treatment were randomly selected and observed every 1 min for time spent grazing, browsing, ruminating and idling. Blood samples were taken once a week during the 2nd (weeks 8, 11 and 14) and 3rd (weeks 18, 19, 20 and 21) trimesters for measurements of some mineral elements and protein metabolites. Goats on natural pasture (NP) grazed 54·8 min (P<0·001) more and browsed 53 min (P<0·001) less than goats on Leucaena leucocephala-grass pasture (LGP) during the 2nd trimester. During the 3rd trimester, goats on NP treatments grazed and idled more (24·7 min, P = 0·004; 15·8 min, P = 0·044, respectively) but ruminated less (−24·1 min, P<0·001) than LGP goats. Time allotted to each field activity by the goats on both treatments within trimester seemed to be dependent on forage species composition while activity between trimesters was possibly influenced by seasons, plant type, herbage quantity, environment and quality, and changes in stage of gestation of the goats. Blood Mg level on NP was higher (P = 0·051) than on LGP during the 2nd trimester while blood Cu and albumin contents on LGP were significantly higher (P = 0·029 and 0·022, respectively) than on NP during the 3rd trimester. Furthermore, blood concentrations of the haematological parameters (except serum protein) on both treatments were within the normal range for goats in the tropics and subtropics and perhaps explain the absence of mineral and nutrient deficiency symptoms. The absence of visible symptoms of mineral deficiency and mimosine toxicity in LGP goats can be attributed to the transfer of DHP-degrading rumen bacteria. The bacteria effectively detoxified mimosine and its metabolites, thereby overcoming chelating tendency of mimosine and its metabolites. Mimosine-susceptible pregnant SAIG can be safely grazed on LGP once their rumen is completely colonized by the DHP-degrading rumen bacteria (Synergistes jonesii).

Temporal dynamics of gradients of phosphorus, ammonium, pH, and electrical conductivity between a di-ammonium phosphate band and wheat roots

Our previous studies have demonstrated that di-ammonium phosphate (DAP) banded into soil led to a rise in pH and EC, and concentrations of NH4+ and bicarbonate-extractable phosphorus around the band. When these chemical gradients develop too close to plant roots, they may cause toxicity and stop root growth. However, the temporal dynamics of gradient development and effects on plants are not known. In this study, wheat was grown in specially constructed pots, with DAP banded 2.5 cm below the seed and either 1 or 2.5 cm horizontally from seed. Plants were harvested at different growth stages to establish the temporal variation in soil chemical gradients between the fertiliser band and the plant roots. Visual toxicity symptoms and decreased root and shoot dry weight and root length in the plants growing with DAP banded 1 cm horizontally away from seed were obvious 14 days after sowing, but disappeared after 6 weeks. Plants in that treatment had a significantly lower number of heads than control plants, implying that there was a harmful effect on reproductive growth and yield with DAP banded too close to wheat seed. The pH increased by one unit and EC increased 2-fold in the soil section containing a DAP band 14 days after sowing. By Day 63, the pH peak disappeared and the EC peak in the 1-cm horizontal distance banding treatment shifted toward soil sections containing the highest root density (4 cm away from the seed on the side opposite to where fertiliser was banded). In the 2.5-cm banding treatment, the EC peak disappeared 42 days after sowing. The ammonium peak was measured in the soil section containing the fertiliser band in the 1-cm banding treatment on Day 14, but the peak shifted to the section with the highest root density by Day 42, and disappeared completely by Day 63. The 2.5-cm banding treatment resulted in a lower ammonium peak compared with the 1-cm treatment after 14 and 42 days, and the highest concentration was found in the section with the highest root density by Day 63. Phosphorus concentration gradients were similar to those of ammonium, except that less depletion and movement of P occurred during the 63-day experiment. In conclusion, the chemical gradients around the fertiliser band show strong temporal and spatial dynamics. However, toxicity caused by close banding and hence high concentrations of ammonium in the initial growth stage results in a decreased wheat yield potential.

Modulation of oxidative stress responsive enzymes by excess cobalt

Excess concentration of cobalt in the growth medium produced visual symptoms of toxicity that intensified with increasing level and duration of metal supply. The tissue concentration of cobalt increased with increasing level of supply. Decreased concentrations of chlorophylls and carotenoids and an increased carotenoids/chlorophyll ratio along with a marked increase in the activities of anti-oxidative enzymes, viz. superoxide dismutase (SOD), ascorbate peroxidase (APOD) and nonspecific peroxidase (POD) suggest strong induction of oxidative stress due to excess cobalt in the growth medium. Decrease in the activity of catalase (CAT)—an iron enzyme, may suggest interference of excess cobalt in iron metabolism of plants, particularly above a 50 μM supply. Decrease in hydrogen peroxide with an increase in cobalt supply has been attributed to increased activities of POD and APOD. Increase in dry matter yield of plants supplied 50 μM cobalt and the decrease in lipid peroxidation with increasing cobalt supply in the range 50–200 μM is suggested as a result from depletion of functional iron as phosphate and/or in ferritin. Appearance of the metal specific toxicity is the likely result of damages predominantly due to enhanced reactive oxygen species (ROS) generation at higher, 300–400 μM, cobalt supplies.