Glucosinolate Profiles of Arabidopsis thaliana in Response to Cadmium Exposure

The influence of cadmium on growth, cadmium accumulation, composition, and content of glucosinolates was investigated in Arabidopsis thaliana after 4 weeks of growth in hydroponics. Accumulation of 3,820 and 321 μg Cd g^?1 dry weight in the roots and leaves of A. thaliana, respectively, exposed to 50 μM Cd. Cadmium treatment significantly decreased the total concentration of glucosinolates both in the leaves and roots. Cd-induced alteration of total glucosinolate content in the roots was mainly due to the decrease of indolyl-glucosinolates. In the Cd treatment leaves, significant decreases were, respectively, detected for glucoibervirin and 4-methoxyglucobrassicin (P?<?0.01), while other glucosinolate levels did not decrease significantly. In response to cadmium, the three indolyl-glucosinolates all showed significant decreases in the roots. The distinctive influence of cadmium on glucosinolate profiles in Cd-sensitive A. thaliana may be of great ecological importance, decreasing the resistance to phytophage attack. Taken together, our data is discussed in relation to jasmonic acid and salicylic acid as possible molecules that modulate the alteration of glucosinolate profiles in response to cadmium. The similar effects of Cd treatment on the levels of individual glucosinolates in leaves and roots were observed at higher-concentration cadmium treatment (100 μM Cd).     

Germanium accumulation and toxicity in barley

The accumulation of germanium (Ge) by barley (Hordeum vulgare cv. ‘Arivat') grown at various Ge and pH levels was investigated because Ge is an industrially important metal and bioaccumulation of Ge is a potentially useful means of concentrating this trace metal. Six‐day‐old barley seedlings were grown in perlite and nutrient solution adjusted to a pH of 4.5, 6.0, or 7.5 supplemented with 20, 40,60, or 80 μM Ge for seven days. The plants were divided into roots and shoots after harvesting; the dry weight and Ge content of the individual organs were measured, as was the peroxidase activity in the distal 1 cm of the primary leaves. Barley seedlings accumulated Ge in the roots and shoots; the shoots accumulated Ge linearly as medium Ge concentration increased. The dry weight of the organs was not affected, although necrosis was observed in the primary leaves of the seedlings treated with Ge concentrations greater than 20μM. Peroxidase activity in the primary leaves also increased as the Ge levels in the medium increased which indicated that elevated levels of Ge stimulated leaf senescence. These results demonstrate that barley plants can take up Ge and suggest that Ge is not toxic at the levels that might occur in areas where Ge is normally mined.     

INDUCTION OF OXIDATIVE STRESS AND ANTIOXIDANT ENZYMES BY EXCESS COBALT IN MUSTARD

This study focuses on induction of oxidative stress and antioxidative defense mechanism on exposure to excess cobalt (Co) in mustard (Brassica campestris L.; cv. ‘T-59’) plants grown in refined sand. Plants were grown for 40 days at normal (0.1 μM) Co. Additional cobalt was supplied from d 41 at 6 levels, i.e., 0.1 (control), 100, 200, 300, 400 and 500 μM as cobalt sulfate. The primary site of Co toxicity was shoots where middle leaves developed interveinal chlorosis after three days of excess cobalt supply (>100 μM). At severity these chlorotic spots became necrotic and affected areas appeared dry and papery, at this stage, growth of the plants were completely checked, the upper part of the stem became dry and hanged down. The toxicity of cobalt at d 46, i.e., six days after metal supply, (DAMS) reduced the dry weight, concentrations of chlorophyll a, b and carotenoids in leaves and tissue Fe with decreased activity of catalase and lipid peroxidation. Enhancement in proline concentration and elevated activities of antioxidant enzymes peroxidase, superoxide dismutase and ascorbate peroxidase were observed in leaves and roots in response to excess Co supply in mustard. Cobalt concentration of mustard in leaves and roots, ranged from 200 to 397 μg g^?1 at excess Co as compared to 1.1 to 2.5 μg Co g^?1 dry matter in control (0.1 μM Co).     

Differential response of citrus rootstocks to aluminum levels in nutrient solutions: II. Plant mineral concentrations 2

The objective of this study was to determine relations between Al effects and mineral concentrations in citrus seedlings. Six‐month‐old seedlings of five citrus rootstocks were grown for 60 days in supernatant nutrient solutions of Al, P, and other nutrients. The solutions contained seven levels of Al ranging from 4 to 1655 μM. Al and similar P concentrations of 28 μM P. Aluminum concentrations in roots and shoots increased with increasing Al concentration in the nutrient solution. Aluminum concentrations in roots of Al‐tolerant rootstocks were higher than those of Al‐sensitive rootstocks. When Al concentrations in nutrient solution increased from 4 to 178 μM, the K, Mg, and P concentrations in roots and the K and P levels in shoots increased. Conversely, Ca, Zn, Cu, Mn, and Fe in the roots and Ca, Mg, Cu, and Fe in the shoots decreased. The more tolerant rootstocks contained higher Fe concentrations in their roots than did the less tolerant ones when Al concentrations in solution were lower than 308 μM. Concentrations of other elements (Ca, K, P, Mg, Zn, and Mn) in roots or shoots exhibited no apparent relationship to the Al tolerance for root or shoot growth of the rootstocks. Calcium, K, Zn, Mn, and Fe concentrations in roots and Mg and K concentrations in shoots of all five rootstocks seedlings had significant negative correlations with Al concentrations in corresponding roots or shoots.     

Cadmium Stress in Barley: Growth,Leaf Pigment,and Protein Composition and Detoxification of Reactive Oxygen Species

Barley seedlings (Hordeum vulgare L., cv. ‘Obzor’) were exposed for 5 d to 0, 5, 50, and 500 μM CdCl₂ in nutrient solution. Cadmium (Cd) treatment caused a reduction of plant length, biomass, and leaf pigment content. The level of soluble leaf proteins was not changed significantly. SDS-PAGE revealed a slight diminution of Rubisco subunits and the appearance of a new low molecular mass band after exposure to 50 or 500 μM Cd. The antioxidative protection in leaves under Cd toxicity was studied in its complexity. Slightly diminished superoxide dismutase, enhanced catalase, and drastically increased total peroxidase activities were found at the highest Cd level. Ascorbate peroxidase activity was not changed significantly. The isoenzyme patterns of the antioxidant enzymes under study were only slightly altered without synthesis of new isoforms. The content of oxidized ascorbate increased during exposure to 50 and 500 μM Cd. The level of H₂O₂ rose only at 500 μM Cd without accumulation of malondialdehyde and oxidized proteins. Non-protein thiol groups increased up to four-fold after exposure to 50 and 500 μM Cd. The results are in accordance with the induction of mechanisms allowing an immobilization and sequestration of Cd in barley leaves, and suggest only minor effects via oxidative damage.     

Cadmium toxicity in clones of populus tremula

Four clones of Populus tremula were exposed to 1 μM Cd at pH 3.5 or 5.0. A differing sensitivity between the clones to both pH and Cd was found. The Cd content of the roots was approximately two times that of the leaves in all 4 clones. Cadmium accumulation was affected by the pH of the nutrient solution, but the magnitude of the effect was small. The gas exchange of the clones was found to be affected by pH and Cd supply. At pH 5.0 exposure to 1 μM Cd reduced CO ₂ uptake by 20 to 60 % depending upon the clone investigated. The effect of Cd on gas exchange was greater at pH 5.0 than pH 3.5. At pH 5.0 exposure to 1 μM Cd reduced the chlorophyll level in the leaves by 17 to 34 %. The water content of the leaves was reduced by exposure to Cd at both pH levels.

     

Cadmium‐induced alterations in nutrient composition and growth of betula pendula seedlings: The significance of fine roots as a primary target for cadmium toxicity

Birch seedlings (Betula pendula) were cultivated in nutrient solution with 0–2 μM cadmium (Cd). The effects of 2–10 days of Cd exposure on root and shoot element composition [potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), sulfur (S), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and Cd] and growth (as percentage dry weight increase) were investigated. The element composition of fine roots and remaining root parts were analysed separately to elucidate the significance of the fine roots as a primary target for Cd toxicity. The nutrient composition of the roots was considerably altered by the Cd exposures, whereas the nutrient composition of the shoot was less affected. After eight days, the whole root (fine roots + remaining roots) concentrations of K, Ca, Mg, and Mn were reduced, whereas the opposite was found for Cu and Mo. The element distribution between fine roots and remaining roots was altered by the Cd exposures. Cadmium was accumulated in the roots and in fine roots especially. Fine roots also exhibited a capacity for Cu accumulation and a retainment of Ca and S. Total plant growth was stimulated by 0.05 μM Cd but was reduced by the 0.5–2 μM Cd treatments. Root growth was increased by the Cd exposures and growth reductions were restricted only to the shoot. Accumulation of Cd and Cu and a retainment of Ca and S in the fine roots together with a preference for root growth, imply that the explanation for the Cd effects obtained may include mechanisms for Cd tolerance.     

Interaction between zinc deficiency and boron toxicity on growth and mineral nutrition of sour orange seedlings

Sour orange (Citrus aurantium L.) seedlings were grown for 3 months in diethylenetriamine pentaacetate (DTPA)‐buffered nutrient solutions to study the effect of Zn stress on the plants’ sensitivity to high boron concentration in the root environment. There were three zinc treatments: 21 μM Zn (LOW Zn‐DTPA), 69 μM Zn (NORMAL Zn‐DTPA) in the nutrient solution, or 12 weekly foliar sprays with ZnSO₄ (FOLIAR‐Zn). In the FOLIAR‐Zn treatment, the nutrient solution contained 21 μM Zn. Zn activities calculated with a chemical equilibrium model, Geochem PC, and expressed as pZn=‐log(Zn⁺²), were 10.2 and 9.7 in the LOW Zn‐DTPA and NORMAL Zn‐DTPA nutrient solutions, respectively. One half of the plants in each Zn treatment were grown in 51 μM B (NORMAL‐B) and the other half in 200 μM B (HIGH‐B) nutrient solution. Seedlings grown in LOW Zn‐DTPA/NORMAL‐B nutrient solution developed Zn deficiency symptoms such as: reduced shoot growth, small and chlorotic leaves, and white roots with visibly shorter and thicker laterals than in Zn sufficient plants. The HIGH‐B treatment decreased shoot growth, leaf and stem dry weight, leaf area, and induced severe leaf B toxicity on seedlings grown in the LOW Zn‐DTPA nutrient solution but the effect was either absent or less pronounced in the NORMAL Zn‐DTPA or FOLIAR‐Zn treatments. Seedlings in the LOW Zn‐DTPA FOLIAR‐Zn treatments but they had lower B concentration on a whole plant basis indicating less B uptake per unit of dry weight. The FOLIAR‐Zn and NORMAL Zn‐DTPA treatments were equally effective in alleviating leaf B toxicity symptoms. The FOLIAR‐Zn treatment, however, was less effective than the NORMAL Zn‐DTPA treatment in alleviating the deleterious effect of high B on leaf dry weight even though the B concentrations in leaves, stems, and roots of the foliar‐sprayed seedlings were similar to the NORMAL Zn‐DTPA seedlings. Leaf concentrations of phosphorus, potassium, magnesium, iron, mangenese, and copper were within the optimal range for citrus with the exception of Ca which was low. Although B and particularly Zn treatments modified the concentration of some of these elements in leaves and roots, these changes were too small to explain the observed growth responses. The observation that B toxicity symptoms in Zn‐deficient citrus could be mitigated with Zn applications is of potential practical importance as B toxicity and Zn deficiency are simultaneously encountered in some soils of semiarid zones.     

Effects of Nickel on Growth and Composition of Metal Micronutrients in Barley Plants Grown in Nutrient Solution

Abstract

A hydroponic experiment was conducted in a phytotron at pH 5.5 to study the effects of nickel (Ni) on the growth and composition of metal micronutrients, such as copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn), of barley (Hordeum vulgare L. cv. Minorimugi). Four Ni treatments were conducted (0, 1.0, 10, and 100 μM) for 14 d. Plants grown in 100 μM Ni showed typical visual symptoms of Ni toxicity such as chlorosis, necrosis of leaves, and browning of the root system, while other plants were free from any symptoms. Dry weights were the highest in plants grown in 1.0 μM Ni, with a corresponding increase in the chlorophyll index of the plants, suggesting that 1.0～10 μM Ni needs to be added to the nutrient solution for optimum growth of barley plants. The increase of Ni in the nutrient solutions increased the concentrations of Cu and Fe in roots, while a decrease was observed in shoots. The concentrations of Mn and Zn in shoots and roots of plants decreased with increasing Ni supply in the nutrient solution. Shoot concentrations of Cu, Fe, Mn, and Zn in plants grown at 100 μ M Ni were below the critical levels for deficiency. Plants grown at 1.0 μ M Ni accumulated higher amounts of Cu, Fe, Mn and Zn, indicating that nutrient accumulation in plants was more influenced by dry weights than by nutrient concentrations. The translocation of Cu and Fe from roots to shoots was repressed, while that of Mn and Zn was not repressed with increasing Ni concentration in the nutrient solution.     

Compensatory root growth in winter wheat: Effects of copper exposure on root geometry and nutrient distribution

Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown for seven days in split‐root chambers containing nutrient solutions with various copper chloride (CuCl₂) concentrations [0.5/0.5 (controls), 0.5/2, 0.5/5, 0.5/7 and 0.5/10 μM]. At harvest (day 11), shoot dry weights were about the same in the different copper (Cu) treatments. Dry weights of the root parts exposed to 2–10 μM Cu (Cu‐fed) decreased while they increased for the control roots. A Cu exposure of 2–10 μM severely retarded lateral root initiation and average lateral root length. Average seminal root length was also reduced. The control roots compensated for the retarded growth of the Cu‐fed roots by increasing chiefly in lateral root number, but their average length remained similiar. Phosphorus (P) concentration decreased gradually in all determined plant parts (shoots, Cu‐control and Cu‐fed roots) with increased external Cu concentration. The potassium (K) concentration in the shoots was similarly affected, but it did not decrease in the Cu‐fed roots until the external Cu concentration reached 10 μM. The Cu concentration in the Cu‐fed roots increased proportionally to the external Cu concentration, but Cu was not exported to the other plant parts. The reasons for changes in root geometry and nutrient balance are discussed.     

Under drought conditions NaCl improves the nutritional status of the xerophyte Zygophyllum xanthoxylum but not of the glycophyte Arabidopsis thaliana

Zygophyllum xanthoxylum is a salt‐accumulating xerophytic species with excellent adaptability to adverse environments. Previous studies demonstrated that Z. xanthoxylum absorbs a great quantity of Na⁺ as an osmoregulatory substance under arid conditions. To investigate the nutritional status of Z. xanthoxylum in comparison with a typical glycophyte, Arabidopsis thaliana, seedlings were exposed to NaCl (50 mM for Z. xanthoxylum and 5 mM for A. thaliana), osmotic stress (–0.5 MPa), and osmotic stress combined with the NaCl treatment. Compared to the control, NaCl treatment or osmotic stress significantly increased Na⁺ concentration in leaves and roots of Z. xanthoxylum, but not of A. thaliana. Under osmotic stress, the addition of NaCl significantly increased Na⁺ concentration in leaves and roots of Z. xanthoxylum, resulting in improved biomass and tissue water content. However, such changes were not observed in A. thaliana. Compared to the control, K⁺ concentrations in leaves and roots remained unchanged in Z. xanthoxylum when exposed to osmotic stress, with or without additional 50 mM NaCl. In contrast, significant reductions in shoot K⁺ concentrations of A. thaliana were observed under osmotic stress alone or when combined with 5 mM NaCl. Moreover, NaCl alone or when combined with osmotic stress enhanced the accumulation of N, P, Fe, Si, Ca²⁺, and Mg²⁺ in Z. xanthoxylum, but did not cause such nutritional changes in A. thaliana. Compared to the glycophyte A. thaliana, Z. xanthoxylum could accumulate Na⁺ and maintain the stability of nutritional status at a relatively constant level to cope with drought stress.     

Influence of ca concentration on growth,tissue concentration,and nutrient uptake of in vitro propagated plums and lovell seedlings

Seedlings of ‘Lovell’ peach [Prunus persica (L.) Batsch], and in vitro propagated plums, ‘St. Julien A GF 655–2’ [Prunus institia (L.) Bullace] (655–2), ‘Damas GF 1869’ [Prunus domestica (L.)] (D1869), and ‘Clark Hill Red Leaf’ [Prunus saliciana (Lindl) x Prunus cerasifera (EHRH)] (CH redleaf) were grown in the greenhouse 45 or 51 days in nutrient solutions containing 2, 6, 22, 200, and 400 μM Ca. Terminal length, number of laterals, trunk cross‐sectional area, and root volume were increased by the 22 μM Ca treatments at harvest 1. The CH redleaf and 655–2 plums had the largest increase in growth for harvest 1, but the ‘Lovell’ peach seedlings and D1869 plum had the largest increase in growth for harvest 2. There were no leaf symptoms of Ca deficiency when the leaf Ca concentration in the tissue exceeded 2500 μg/g (dry wt.) Calcium concentration was increased from 1406 to 4109 μg/g (dry wt.) in the stems, and from 540 to 2633 μg/g (dry wt) in the roots by Ca treatments of 400 μM after 45 days of growth. Calcium uptake rate for ‘Lovell’ seedlings was greater than were rates for CH redleaf and 655–2 plums at all solution concentrations during the first 45 days of growth. The Ca uptake rate for D1869 plum was greater than the rate for ‘Lovell’ seedlings during the second growth period. An interaction between Ca concentration and plant species occurred for P, K, and Mg uptake rates at both harvest dates. The in vitro propagated D1869 plum was equal to the ‘Lovell’ seedlings in growth, tissue Ca concentration, and Ca uptake rates.     

Aluminum toxicity in tomato. Part 1. growth and mineral nutrition

Aluminum (Al) toxicity was studied in two tomato cultivars (Lycopersicon esculentum Mill. ‘Mountain Pride’ and Floramerica') grown in diluted nutrient solution (pH 4.0) at 0, 10, 25, and 50 μM Al levels. In the presence of 25 and 50 μM Al, significant reduction was found in leaf area, dry weight, stem length, and longest root length of both cultivars. Growth of ‘Floramerica’ was less sensitive to Al toxicity than growth of ‘Mountain Pride’. Elemental composition of the nutrient solutions were compared immediately after the first Al addition and four days later. The uptake of micronutrients copper (Cu), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B), and iron (Fe) from the nutrient solution was reduced in both cultivars with increasing Al levels. Nutrient solution Al gradually decreased in time for every treatment; less in cultures of ‘Floramerica’ than in ‘Mountain Pride’. Aluminum treatments decreased the calcium (Ca), potassium (K), magnesium (Mg), Mn, Fe, and Zn content in the roots, stems, and leaves. Aluminum treatment promoted the accumulation of P, Mo, and Cu in the roots, and inhibited the transport of these nutrients into stems and leaves. At 25 and 50 μM levels of Al, lower Al content was found in the roots of cv. “Floramerica’ than in the roots of cv. ‘Mountain Pride’.     

Effects of sulfur supply on soybean plants exposed to zinc toxicity

Application of most waste or by‐product material increases the zinc (Zn) concentration in soils markedly. This investigation was conducted to determine if enhanced sulfur (S) supplied as sulfate (SO₄) would modify the toxic effects of excess Zn. Soybean (Glycine max [L.] Merf. cv. Rarisorri) was grown for two weeks in nutrient solutions containing ranges in Zn (0.8 to 80 μM) and S (0.02 to 20 mM). Root and shoot conditions were observed, dry weights measured, and Zri concentration determined. Zinc‐toxicity symptoms started about one week after transplanting young plants to nutrient solutions. Symptoms including chlorosis, especially in the trifoliate leaves, and change in orientation of unifoliate leaves were mild in 20 μM‐, intermediate in 40 μM‐, and severe in 80 μM Zn‐containing solutions. Dry weight was reduced in plants exposed to 20, 40, and 80 μM Zn. Plants grown in 40 μM Zn and 20 mM S survived longer than those grown in lower S concentrations and showed alleviation of the chlorosis in trifoliate leaves. The change in the orientation of the unifoliate leaves due to Zn toxicity, however, was not affected by S. Zinc contents in shoots grown at toxic Zn levels were higher in 20 mM‐ than in lower S‐containing nutrient solutions. High S supply (20 mM) increased Zn translocation from roots to shoots. Besides increasing the Zn translocation from roots to shoots, it seems that S nutrition may also be a factor helping the plants to cope with high levels of Zn in their tissues.     

Long-Term Effects of Aluminum and Cadmium on Growth,Leaf Anatomy,and Photosynthetic Pigments of Cotton

Aluminum (Al) and cadmium (Cd) are two elements that contaminate soil in different ways as waste products of some industrial processes and that can be tolerated by some plant species in different concentrations. In this study, growth parameters of leaves and stems (fresh and dry weights, stem lengths, leaf surface area, and lamina thickness), anatomical changes in leaves (lower and upper epidermis, stomata and mesophyll tissue), and photosynthetic pigment contents (chlorophyll a and b, total chlorophyll, and carotenoids) were investigated in cotton (Gossypium hirsutum L. cv. Nazilli 84S), which was treated with Al and Cd for 3 months. Cotton seedlings were grown in greenhouse conditions and watered with Hoagland nutrient solutions, which contained 0, 100, and 200 μM aluminum chloride (AlCl₃) and cadmium chloride (CdCl₂). It was observed that reduced soil pH positively affected many parameters in cotton plants. Aluminum accumulation was greater in leaves than stems while the opposite was true for Cd accumulation. Leaves and stems of cotton plants treated with 100 and 200 μM Al and Cd showed slight growth changes; however, high concentrations of Al (200 μM) caused significant reductions in leaf area and leaf fresh weight, whereas stem fresh weight decreased with 200 μM Cd treatment. Anatomical parameters were mostly affected significantly under both concentrations of Al and Cd solutions (100 and 200 μM). The results revealed that the anatomical changes in the leaves varied in both treatments, and the long-term effect of the tested metals did not include harmful effects on anatomical structures. Moreover, the variations could be signals of tolerance or adaptive mechanisms of the leaves under the determined concentrations.     

Effects of Manganese Deficiency on Growth and Contents of Active Constituents of Glycyrrhiza uralensis Fisch.

To investigate effects of manganese (Mn) deficiency (0 μM L^–1) on concentrations of chlorophyll, superoxide dismutase (SOD) activity, biomass, and accumulations of active constituents in Glycyrrhiza uralensis Fisch., seedlings of 1-year-old G. uralensis were grown in a nutrient solution for 60 days. In this experiment, three concentrations of Mn were set up: 0 (–Mn), 7 μM L^–1, and 14 μM L^–1 Mn. The results showed that –Mn decreased the concentration of chlorophyll a with no significant differences in concentrations of chlorophyll b, total chlorophyll a + b, carotenoids, and chlorophyll a/b ratio. On days 45 and 60, SOD activity significantly decreased. However, dry weight of roots under –Mn showed no significant difference during the whole experiment. The accumulations of glycyrrhizic acid and liquiritin were significantly inhibited by Mn deficiency at different times. Thus results indicated that Mn deficiency could affect growth and contents of its secondary metabolites of G. uralensis.     

Toxicity of copper and zinc in seedlings of Mung bean and inducing accumulation of polyamine

A solution culture was conducted to investigate the effects of copper (Cu) and zinc (Zn) toxicity on growth of mung bean (Phaseolus aures Roxb. cv VC‐3762) and accumulation of polyamine. Eight‐day‐old seedlings were grown in diluted nutrient solution with different concentrations of Cu and Zn for 6 days. Results showed that elongation of epicotyl and fresh weight of plants were decreased by 10 μM Cu and 100 μM Zn significantly compared to control (0.03 μMCu and 0.1 μMZn). Accumulation of polyamine, especially putrescine (Put) was found in the epicotyl of mung bean seedlings. Addition of 5 mM calcium (Ca) into nutrient solution improved the growth of 10 μM Cu‐treated seedling, and decreased the concentration of Put and increased concentrations of spermine and spermidine in epicotyl of plants. Moreover, supplying Put did not increase tolerance of plant to Cu or Zn. It was suggested that Put accumulation resulting from toxicity of Cu and Zn might merely be a symptom of stress injury.     

Preferential translocation of boron to young leaves in Arabidopsis thaliana Regulated by the BOR1 Gene

A mutant of Arabidopsis thaliana, bor1-1 (Noguchi et al. 1997: Plant Physiol., 115, 901–916) requires high levels of boron (B) for normal growth. We analyzed the B-deficiency symptoms of bor1-1 mutant plants in detail. A low B supply retarded the growth of the mutant plants more evidently in leaves than in roots. In particular, cell expansion and formation of air spaces were severely impaired by B deficiency in young rosette leaves. Such defects in growth were correlated with the reduced contents of B in leaves. These defects were not observed when a sufficient amount of B was supplied. Uptake experiments with ¹⁰B-enriched tracer B demonstrated that B taken up through roots was preferentially transported to young leaves compared to old leaves in the wild-type plants under a low B supply. Such a preferential transport to young leaves was not evident in the mutant plants. In conclusion, our data demonstrated that in A. thaliana plants B is preferentially transported to young organs under a low B supply and that this transport process is controlled at least in part by the BOR1 gene.     

Ammonium uptake capacity and response of cytosolic glutamine synthetase 1;2 to ammonium supply are key factors for the adaptation of ammonium nutrition in Arabidopsis thaliana

Plant requires nitrogen for the growth, and it use nitrate and ammonium from the environment. Plant suffers from the toxicity when excess ammonium is supplied as a sole nitrogen, although it could be a good nitrogen source for plant growth. We hypothesized that the different responses of ecotypes to ammonium nutrient could partly account for the adaptation of Arabidopsis to an ammonium environment. The purpose of this study is to understand the different responses of ecotypes in ammonium environment. The growth of Arabidopsis thaliana ecotypes, Columbia was compared to those of Arabidopsis thaliana ecotypes, Landsberg erecta in ammonium nutrient. The ratio of shoot dry weight to root dry weight was compared to evaluate the adaptation of two ecotypes. The shoot:root ratio of Landsberg was significantly higher than that of Columbia. T-DNA insertion in cytosolic glutamine synthetase 1;2, one of the essential ammonium assimilatory enzymes, led a decrease of shoot:root ratio. We also measured the isotope-labeled ammonium uptake and the expression levels of ammonium transporter genes, and also the expression of ammonium assimilatory genes, glutamine synthetase genes and glutamate synthase genes, in roots after ammonium re-supply using real-time polymerase chain reaction analysis. We found that (1) ammonium uptake of Landsberg erecta was higher than that of Columbia, when ammonium was supplied at higher concentration, and (2) cytosolic glutamine synthetase 1;2 was highly increased by ammonium supply in the root of Landsberg erecta. The present study suggested the importance of these two factors for adaptation of Arabidopsis to an ammonium-rich environment.