MINERAL NUTRIENT CONTENT OF TOMATO PLANTS IN AQUAPONIC AND HYDROPONIC SYSTEMS: EFFECT OF FOLIAR APPLICATION OF SOME MACRO- AND MICRO-NUTRIENTS

Effects of foliar applications of some micro- and macro-nutrients on mineral nutrient content of tomato leaves and fruits were investigated in an aquaponic system in comparison with a hydroponic system. Fourteen days old tomatoes seedlings were transplanted on to growth bed of aquaponic and hydroponic systems. Foliar nutrients application began 30 days after transplantation. Eight treatments were used, untreated control and foliar application at the rate of 250 mL plant^?1 with 0.5 g L^?1 potassium sulfate (K₂SO₄), magnesium sulfate (MgSO₄ 7H₂O), ferrous (Fe)- ethylenediamine-N,N′-bis (EDDHA), manganese sulfate (MnSO₄ H₂O), boric acid (H₃BO₃), zinc chloride (ZnCl₂), and copper sulfate (CuSO₄ 5H₂O). Foliar application of potassium (K), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) increased their corresponding concentrations in the leaves of aquaponic-treated plants. On the other hand, foliar spray of K, Fe, Mn, Zn, and Cu caused a significant increment of applied element concentrations in the fruits of hydroponic-grown plants. These findings indicated that foliar application of some elements can effectively alleviate nutrient deficiencies in the leaves of tomatoes grown on aquaponics.     

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.     

Nutrient Dynamics in Orange Trees: The Effect of Soil Fertility

Lime-induced iron (Fe) chlorosis is a nutritional disorder common in calcareous soils, which may result from a low level of Fe available or adverse factors that inhibit Fe mobilization and uptake by plants. Organic-matter amendments can prevent or correct Fe chlorosis in plants but the effect of endogenous soil organic matter (SOM) on this disorder is not known. The main subject of this work was to investigate the consequence of two contrasting levels of soil fertility on the nutritional status of an orange grove [Citrus sinensis (L.) Osb. cv. Valencia Late]. The field experiment was conducted in a commercial citrus grove using mature trees distributed in two plots with different values of SOM, phosphorus (P), and potassium (K), but with the same level of active lime. The concentration of nitrogen (N), P, K, magnesium (Mg), calcium (Ca), Fe, copper (Cu), zinc (Zn), and manganese (Mn) in young and mature leaves and flowers was evaluated. The level of Mg and the Mg/Zn ratio in flowers from both plots, although significantly different, only indicated moderate Fe chlorosis, as predicted by a previously developed model, and was consistent with the amount of chlorophyll present in the leaves. However, nutrient partitioning between leaves of contrasting age was very different. Mature leaves from trees grown in the high-fertility plot (HF) had larger concentrations of N, P, and K but lower concentrations of Ca, Fe, and Mn than did those from the low-fertility plot (LF). Young leaves from the LF had more N, P, Mg, Cu, and Mn and less Ca and Fe than did those from the HF. Flower analysis, although useful to predict Fe chlorosis, failed to detect differences in the nutritional status of plants resulting from contrasting levels of soil fertility. Furthermore, endogenous SOM had only a marginal effect on Fe chlorosis.     

Morphological Changes in Leaves of Mexican Lime Affected by Iron Chlorosis

Iron (Fe) chlorosis reduces the concentration of photosynthetic pigments, photosynthates, and crop yield. The effect of Fe chlorosis on leaf composition and cell structure was evaluated in Mexican lime (Citrus aurantifolia) with different degrees of Fe chlorosis. Iron chlorosis significantly reduced concentrations of chlorophylls a, b, and a + b, and caused thickening of leaves, due to the increase in palisade and spongy parenchyma cells. The chloroplasts of the chlorotic and albino leaves showed a disorganized ultrastructure; they had an elongated shape with disarrayed thylakoids, underdeveloped grana, scarce starch granules, and hole-like folds in the thylakoid membranes. The accumulation of calcium oxalate crystals in the upper and lower sides of the epidermis, crystal length, and total crystal content increased with Fe chlorosis severity. The green leaves, in contrast, had chloroplasts with typical ultrastructure. The degree of Fe chlorosis in the leaves significantly affected the concentrations of potassium (K); Fe, manganese (Mn), Fe²⁺, and the phosphorus (P)/Fe and K/calcium (Ca) ratios.     

Effect of chromium VI on mineral element composition of bush beans

Bush beans (Phaseolus vulgaris L. cv Contender) were grown on perlite with nutrient solution and 0, 1, 2.5 and 5 ppm levels of Na₂CrO₄ Significant decrease of top growth and chlorosis in trifoliated leaves were observed for 2.5 and 5 ppm Cr, with Cr concentrations (μg/g) in tops:≥ 12.1, in roots:≥ 509.9. Cr decreased K, Na, Mg and Fe concentrations, and increased P and Mn concentrations in roots. In tops decreased N, K, Na and Fe concentrations and increased Mn and Ca concentrations were observed, Translocation of P, Zn, Cu and Fe was inhibited; Ca and Mn translocation was generally enhanced. P/Fe ratio was increased up to 60% in chlorotic plants, indicating a shift from Fe²⁺ to Fe³⁺.     

Iron‐manganese interactions among clones of Nilegrass

Tetraploid clones of Nilegrass (Acroceras macrum, Stapf.) develop a chlorosis resembling iron (Fe) deficiency on acid (pH 5.0) soils in the Midlands of KwaZulu, Natal, South Africa. Hexaploid and pentaploid clones appear more resistant to the disorder. Iron deficiency would not be expected in such acid soils, but foliar sprays of Fe sulfate reduce the symptoms within 24 hours. Aluminum (Al) toxiciry has been ruled out as a cause of this chlorosis on the basis of soil tests. Manganese (Mn)‐induced Fe deficiency has been postulated. Six Nilegrass clones, differing in ploidy levels, were grown under low Fe or high Mn levels in nutrient solutions, in Mn‐toxic soil, in calcareous soil and in a standard potting soil at pH 7.0. Differential chlorosis symptoms, similar to those observed in the field, were reproduced in plants grown in low Fe or high Mn solutions, in neutral potting soil and in calcareous soil at pH 7.8. Based on plant symptoms and dry weights, the tetraploids were generally more sensitive to these conditions than hexaploid or pentaploid clones. However, in Mn‐toxic soil, plants had leaf tip necrosis rather than the chlorosis typical of Fe deficiency. When grown in a standard potting soil at pH 7.0, plants showing chlorosis accumulated higher concentrations of phosphorus (P), Al, copper (Cu), Mn, Fe, and zinc (Zn) than non‐chlorotic plants. Differential susceptibility to chlorosis is apparently associated with interference of such elements in Fe metabolism, and not with differential Fe concentrations in plant shoots. Additional studies are needed to determine the chemical states of Fe and Mn in root zones and within plant shoots of these clones. Resolution of the differential chlorosis phenomenon would contribute to fundamental knowledge in mineral nutrition and could be helpful in tailoring plant genotypes to fit problem soils.     

Foliar Symptomology and Tissue Concentrations of Nutrient‐Deficient Vegetative Strawflower Plants

Abstract

Elemental deficiencies of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, copper, zinc, or boron (N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, or B) were induced in plants of Florabella Pink strawflower [Bracteantha bracteata (Vent.) A. A. Anderberg]. Rooted stem cuttings were planted in 4.87‐L plastic containers and fertilized with a complete modified Hoagland's solution or this solution minus the element that was to be investigated. Plants were harvested for tissue analyses as well as dry weights when initial foliar symptoms were expressed and later under advanced deficiency symptoms. Deficiency symptoms for all treatments were observed within 7 weeks. The most dramatic expression of foliar symptoms occurred with N (chlorotic lower foliage leading to necrotic margins on the mature leaves), Ca (black necrotic spots on the tips of the young leaves), S (uniform chlorosis of young leaves and recently mature leaves), B (thick, leathery, and deformed young leaves), Fe (uniform yellowish‐green chlorosis on the young leaves), and Zn (brownish‐gray necrosis on the tips of the mature leaves). At the initial stage, only Fe‐deficient plants weighed less than the control, whereas K‐, Ca‐, and Mg‐deficient plants had greater dry weights than plants receiving the complete modified Hoagland's solution (control plants). Dry weights of plants treated with solutions not containing N, P, Ca, S, Cu, or Mn were significantly lower when compared with the control plants under an advanced deficiency. Foliar‐tissue concentration data will assist plant‐tissue analysis laboratories in establishing foliar symptom standards for growers.     

IS CHLOROPHYLL FLUORESCENCE TECHNIQUE A USEFUL TOOL TO ASSESS MANGANESE DEFICIENCY AND TOXICITY STRESS IN OLIVE PLANTS?

A 130-day hydroponic experiment was carried out in a glasshouse to examine whether manganese (Mn) concentration in the nutrient solution affects the nutritional status of olive plants and to find out whether the chlorophyll fluorescence technique is suitable to assess Mn toxicity and/or deficiency stress in olive plants prior to the appearance of these two nutritional disorders. For this purpose, chlorophyll fluorescence parameters (F_v/F_m and F_v/F₀ ratios) were recorded every 40 days in the leaves of ‘Kothreiki’ and ‘FS-17’ olive cultivars, which were irrigated with Hoagland's nutrient solutions containing various Mn concentrations. In parallel the elongation of the main shoot of all experimental plants, as well as the concentrations of Mn, iron (Fe), zinc (Zn), boron (B), phosphorus (P), calcium (Ca), magnesium (Mg), and potassium (K) in their leaves were recorded. The following Mn treatments were applied: 0 μM Mn (to induce Mn deficiency), 40 μM Mn (to promote normal growth), and 640 μM Mn (to induce Mn toxicity). Our results indicated that not only the rate of shoot elongation but also the fluctuation with time of the leaf concentrations of all determined mineral elements (except for Mn) was not significantly affected by the Mn concentration in the nutrient solution, irrespectively of the cultivar. This was not observed with regard to the time variation of the F_v/F_m and F_v/F₀ ratios, where the values of these parameters were significantly reduced in the 640 μM Mn treatment at the 80th and 130th day of the experiment in both olive cultivars, compared to the relevant previous ones (those of the days 0 and 40th), something which did not happen in the other two Mn treatments (0 and 40 μM). However, in none of the two cultivars tested and in any of the three Mn treatments (0, 40 and 640μM) the F_v/F_m and F_v/F₀ ratios did not drop below the critical values of 0.8 and 4, respectively, even at the end of the experiment, where high Mn concentrations were found in the leaves of both cultivars treated with 640 μM Mn (616 μg g^?1 d.w. in ‘FS-17’ and 734 μg g^?1 d.w. in ‘Kothreiki’). Symptoms of Mn toxicity (curling and brown speckles) were observed in the top leaves of both cultivars, after the 90th day of the experiment. At the same time, the final leaf Mn concentrations (those of the 130th day of the experiment) in plants grown under 0 μM Mn were 23 μg g^?1 d.w. in ‘FS-17’ and 20 μg g^?1 d.w. in ‘Kothreiki’, i.e., a little above of the deficiency range (<20 μg g^?1 d.w.). At the 130th day, Mn concentration in nutrient solution, as well as Mn concentration in the leaves of both olive cultivars was negatively correlated with the leaf concentration of Fe and the values of the F_v/F_m and F_v/F₀ ratios, and positively with the concentrations of Zn and P in the leaves. Finally, the periodical measurement of the F_v/F_m and F_v/F₀ ratios was proved to be a non-reliable means to predict the appearance of the visible symptoms of Mn toxicity in olive leaves (although their values declined significantly at the 80th and 130th day of the experiment in both olive cultivars).     

苹果MxNas1基因正反义表达载体构建及转化烟草的研究

为研究笔者前期克隆的MxNas1基因功能,构建了苹果属植物小金海棠MxNas1基因正义和反义两种表达载体,并用农杆菌介导的叶盘转化法转化了烟草.对转基因烟草分别进行0和1μmol/L Fe处理14d后,转正义载体烟草在缺Fe情况下叶片没有黄化,表现出较强的抗缺Fe能力;转反义载体植株比对照烟草幼叶提前出现黄化现象,表现...     

Nitrate/ammonium ratio effects on mineral element uptake by sorghum 1

Abstract

Experiments were conducted using different NO₃ ^–/NH₄ ⁺ ratios to determine the effects of these sources of N on mineral element uptake by sorghum [Sorghum bicolor (L.) Moench] plants grown in nutrient solution. The NO₃ ^–/NH₄ ⁺ ratios in nutrient solution were 200/0, 195/5, 190/10, and 160/40 mg N L^–1. Nutrient solutions were sampled daily and plants harvested every other day during the 12‐day treatment period.

Moderately severe Fe deficiencies were observed on leaves of plants grown with 200/0 NO₃ ^–/NH₄ ⁺ solutions, but not on the leaves of plants grown with the other NO₃ ^–/NH₄ ⁺ ratios. As plants aged, less Fe, Mn, and Cu were translocated from the roots to leaves and leaf/root ratios of these elements decreased dramatically in plants grown with 200/0 NO₃ ^–/NH₄ ⁺ solutions. Extensive amounts of Fe, Mn, and Cu accumulated in or on the roots of plants grown with 200/0 NO₃ ^–/NH₄ ⁺ solutions. Manganese and Cu may have interacted strongly with Fe to inhibit Fe translocation to leaves and to induce Fe deficiency. As the proportion of NH₄ ⁺ in solution increased, K, Ca, Mg, Mn, and Zn concentrations decreased in the leaves, and Ca, Mg, Mn, and Cu concentrations decreased in roots. Potassium and Zn tended to increase in roots as NH₄ ⁺ in solution increased.     

Alleviation of manganese toxicity and manganese-induced iron deficiency in barley by additional potassium supply in nutrient solution

Barley plants were grown hydroponically at two levels of K (3.0 and 30 mm) and Fe (1.0 and 10 μm) in the presence of excess Mn (25 μm) for 14 d in a phytotron. Plants grown under adequate K level (3.0 mm) were characterized by brown spots on old leaves, desiccation of old leaves, interveinal chlorosis on young leaves, browning of roots, and release of phytosiderophores (PS) from roots. These symptoms were more pronounced in the plants grown under suboptimal Fe level (1.0 p,M) than in the plants grown under adequate Fe level (10 μm). Plants grown in 10 μm Fe with additional K (30 mm) produced a larger amount of dry matter and released less PS than the plants grown under adequate K level (3.0 mm), and did not show leaf injury symptoms and root browning. On the other hand, the additional K supply in the presence of 1.0 μM Fe decreased the severity of brown spots, prevented leaf desiccation, and increased the leaf chlorophyll content, which was not sufficient for the regreening of chlorotic leaves. These results suggested that the additional K alleviated the symptoms of Mn toxicity depending on the Fe concentration in the nutrient solution. The concentration (per g dry matter) and accumulation (per plant) of Mn in shoots and roots of plants grown in 10 μm Fe and 30 mm K were much lower than those of the plants grown in 10 μm Fe and 3.0 mm K, indicating that additional K repressed the absorption of Mn. The concentration and accumulation of Fe in the shoots and roots of the plants grown in 10 μm Fe and 30 mm K were higher than those of the plants grown in 10 μm Fe and 3.0 mm K, indicating that the additional K increased the absorption of Fe under excess Mn level in the nutrient solution. The release of PS, chlorophyll content, and shoot Fe concentration were closely correlated.     

Einfluß von Bikarbonat auf die subzelluläre Verteilung von blatt- und wurzelappliziertem Eisen bei Sonnenblumen (Helianthus annuus L.)

Influence of bicarbonate on the subcellular distribution of iron applied to roots or leaves of sunflower (Helianthus annuus L.) 18 days old sunflower seedlings were transferred and cultivated for 9 days ( untill chlorosis appeared) in nutrient solutions. After that Fe concentration of roots and shoots and the subcellular distribution of Fe in the cytoplasm of the young leaves was determined. Bicarbonate in the nutrient solution with Fe reduced the concentration of Fe and chlorophyll in the young leaves of the plants, also the concentration of Fe and protein in the chloroplast fraction of the cytoplasm, but the subcellular distribution for Fe remained unchanged compared with the control. Leaf spray with Fe-EDTA to plants in nutrient solution without Fe + bicarbonate resulted in higher Fe but unchanged chlorophyll concentrations in the young leaves, while the cytoplasm fractions of these leaves had higher concentrations of iron and protein compared with the control. An inactivation of leaf iron by bicarbonate in the nutrient medium could not be demonstrated. There was no significant lowering of the concentration of disolved Fe in the nutrient solution by bicarbonate, indicating a disturbance of Fe-up-take rather than an insufficient Fe-supply as a factor for iron chlorosis. The physiological activity of leaf applied Fe was not diminished by bicarbonate in the nutrient solution. This observation too points to a primary effect of bicarbonate in the root area. The pH of the cytoplasm from young leaves remained unchanged after leaf spraying with Fe-EDTA. In spite of this there might be a local effect of sprayed solution (with pH 5,1) on the pH of solutes in the apoplast, influencing the mobility of leaf applied Fe.     

Physiological and Mineralogical Properties of Arsenic-Induced Chlorosis in Barley Seedlings Grown Hydroponically

The experiment was carried out to investigate the effects of arsenic (As) on the physiological and mineralogical properties of barley (Hordeum vulgare L. cv. ‘Minorimugi’). The plants were grown in nutrient solution treated with 0, 6.7, 33.5, and 67 μ M As (0, 0.5, 2.5, and 5 ppm As, respectively) in the phytotron. Dry matter yield of shoots and roots decreased significantly with the As treatments, indicating that barley plants are As-sensitive and As-toxicity depends on the As concentration in the rooting medium. Necrosis in older leaves and chlorosis symptoms (whitish color) in the fully developed young leaves were observed at the 33.5 and 67 μ M As treatments. Arsenic concentration, accumulation, and translocation increased with the increase of As concentration in the rooting medium. Arsenic was mostly concentrated in roots and a little amount was moved to shoots, indicating that As was not easily translocated to shoots of barley seedlings. Concentrations and accumulations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), zinc (Zn), and copper (Cu) decreased significantly in shoots for 33.5 and 67 μ M As treatments as compared to the 0 μ M As treatment. Concentrations of P, K, Ca, Mg, Mn, and Cu decreased in roots, but Zn concentration increased in roots at 67 μ M As treatment. Accumulations of P, K, Ca, Mg, Mn, Zn, and Cu in roots also decreased significantly at 67 μ M As treatment. Accumulation of P and the cations showed negative relationship with As. Concentration of Fe decreased in shoots at 33.5 and 67 μ M As treatments where chlorosis was induced in the young leaf but increased in roots at 33.5 and 67 μ M As treatments. It was suggested that As might induce iron (Fe)-chlorosis in the plants. Among the micronutrients, Fe translocation was more affected than others by As. Phytosiderophore (PS) accumulation in roots, which is a symptom of Fe-deficiency in grasses, did not change significantly between 0 and 33.5 μ M As treatments; indicating that As-induced chlorosis did not enhance PS accumulation in roots and decreased due to As-toxicity at 67 μ M As treatment.     

Root and Leaf Ferric Chelate Reductase Activity in Pond Apple and Soursop

Abstract

Root and leaf ferric chelate reductase (FCR) activity in Annona glabra L. (pond apple), native to subtropical wetland habitats and Annona muricata L. (soursop), native to nonwetland tropical habitats, was determined under iron (Fe)-sufficient and Fe-deficient conditions. One-year-old seedlings of each species were grown with 2, 22.5, or 45 µM Fe in a nutrient solution. The degree of tolerance of Fe deficiency was evaluated by determining root and leaf FCR activity, leaf chlorophyll index, Fe concentration in recently mature leaves, and plant growth. Root FCR activity was generally lower in soursop than in pond apple. Eighty days after plants were put in nutrient solutions, leaf FCR activity of each species was lower in plants grown with low Fe concentrations (2 µM) than in plants grown with high (22.5 or 45 µM) Fe concentrations in the nutrient solution. Leaves of pond apple grown without Fe became chlorotic within 6 weeks. The Fe level in the nutrient solution had no effect on fresh and dry weights of soursop. Lack of Fe decreased the leaf chlorophyll index and Fe concentration in recently matured leaves less in soursop than in pond apple. The rapid development of leaf chlorosis in low Fe conditions and low root and leaf FCR activities of pond apple are probably related to its native origin in wetland areas, where there is sufficient soluble Fe for adequate plant growth and development. The higher leaf FCR activity and slower growth rate of soursop compared to pond apple may explain why soursop did not exhibit leaf chlorosis even under low Fe conditions.     

Accumulation of Mn in Leaves of Rosmarinus officinalis Cultivated in Substrates of Pine Bark

Rosmarinus officinalis is an important aromatic shrub cultivated for medicinal, culinary, and ornamental uses. To assess growth, the contents of trace metals cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), lead (Pb), and zinc (Zn) and macronutrients calcium (Ca), magnesium (Mg), potassium (K), nitrogen (N), and phosphorus (P) were measured in these plants cultivated on two substrates: pine bark (PB, pH 4.0, 80.5% organic matter) and pruning wastes–biosolids (BS, pH 6.9, 47.5% organic matter). These plants, initially of 3.5 ± 0.5 g dry weight and 31.1 ± 6.9 cm, were maintained under greenhouse conditions for 7 months. Nutrient solution samples were taken from each substrate in situ by rhizon probes, indicating that the concentrations of soluble Mn and Zn in PB were significantly greater than in the nutritive solution BS. At the end of the assay, the dry weight of leaves and height was significantly greater in plants cultivated in BS (40.0 ± 2.2 g and 75.9 ± 14.3 cm) than in PB (27.5 ± 4.0 g and 62.4 ± 10.2 cm). Plants cultivated in PB showed slight chlorosis, attributed to the high concentration of Mn in leaves (106.6 ± 7.8 mg kg^?1), which was much greater than in plants cultivated in BS (8.2 ± 0.9 mg kg^?1). The concentration of toxic metals Cd and Pb in plants cultivated on both substrates did not exceed the recommended levels for consumption of the leaves as condiment. If R. officinalis is cultivated on the substrate of pine bark to acid pH for food or medicinal use, the accumulation of Mn must be considered.     

Responses of cucumber grown in recirculating nutrient solution to gradual Mn and Zn accumulation in the root zone owing to excessive supply via the irrigation water

A standard and a high manganese (Mn) level (10 and 160 μM) were combined with a standard and a high zinc (Zn) level (4 and 64 μM) in the nutrient solution supplied to cucumber in closed‐cycle hydroponic units to compensate for nutrient uptake. The concentrations of all nutrients except Mn and Zn were identical in all treatments. The objectives of the experiment were to establish critical Zn and Mn levels in both nutrient solutions and leaves of cucumber grown hydroponically, to assess the impact of gradual Zn and/or Mn accumulation in the external solution on nutrient uptake and gas exchange, and to find whether Mn and Zn have additive effects when the levels of both ions are excessively high in the root zone. The first symptoms of Mn and Zn toxicity appeared when the concentrations of Mn and Zn in the leaves of cucumber reached 900 and 450 mg kg^–1 in the dry weight, respectively. Excessively high Mn or/and Zn concentrations in the leaves reduced the fruit biomass production due to decreases in the number of fruits per plant, as well as the net assimilation rate, stomatal conductance, and transpiration rate, but increased the intercellular CO₂ levels. Initially, the Mn or Zn concentrations in the recirculating nutrient solution increased rapidly but gradually stabilized to maximal levels, while the corresponding concentrations in the leaves constantly increased until the end of the experiment. The uptake of Mg, Ca, Fe, and Cu was negatively affected, while that of K and P remained unaffected by the external Mn and Zn levels. The combination of high Mn and Zn seems to have no additive effects on the parameters investigated.     

Nitric acid‐ and o‐phenanthroline‐extractable iron for diagnosis of iron chlorosis in citrus lemon trees

Abstract

Plant analysis for total iron (Fe) is frequency used for diagnosis of Fe‐deficiency chlorosis. However, chlorotic plants frequency contained similar or higher amount of total Fe than the healthy green plants. The objectives of this study were to (i) determine if Fe chlorosis in citrus lemon can be diagnosed by total or active Fe and can be related to the degree of chlorosis, and (ii) determine the optimum extraction time and ratio of extracting solution to plant sample for extracting the active Fe. Leaf samples of different degrees of Fe chlorosis were sampled from different citrus lemon trees from three different sites. Total Fe was extracted with nitric acid (HNO₃) and active Fe with o‐phenanthroline from lemon leaves. An extraction time of 20 and 45 hours and the ratios of the extractor to the sample of 5:l, 10:1, and 20:1 were investigated. The results indicated that an extraction time of 20 hours is enough for extracting the active Fe from citrus lemon leaves by o‐phenanthroline. The amount extracted by all ratios (5:1, 10:1, and 20:1) were detectable and at the same time similarly and consistency showed the differences in degrees of chlorosis in all plant samples. Total Fe content was always higher in moderately and severely chlorotic leaves compared to the green leaves and was not related to the degree of chlorosis. Therefore, total Fe cannot be used as a criteria to differentiate between the Fe‐deficient and non‐deficient plants. On the other hand, active Fe tended to decrease with the increase in the degree of chlorosis. The ratio of active to total Fe was calculated and was found to be closely correlated with the degree of chlorosis. This clearly illustrates the failure of plant analysis for total Fe and the effectiveness of active Fe and/or the ratio of active to total Fe for diagnosing Fe chlorosis.     

Effect of Various Nitrogen Forms on the pH in Leaf Apoplast and on Iron Chlorosis of Glycine max L.

The effect of NH₄NO₃ (control) and increasing NO₃- levels in nutrient solutions containing no and 100 μM Fe respectively on iron chlorosis of Glycine max was investigated. After two weeks of growth apoplastic pH in excised leaves was measured by means of fluorescence. In plants growing without Fe supply increasing concentrations of NO₃- in the nutrient solution which also was applied to the cut end of the petiole, resulted in a pH increase in the leaf apoplast from 5.34 (NH₄NO₃) to 5.50 (NO₃-) associated with chlorosis observed with intact plants. A close negative correlation was found between chlorophyll concentration and pH in the apoplast (r = ?0.97). While leaves in the treatment exclusively fed with NO₃- were strongly chlorotic, those in the NH₄NO₃ treatment were green. With exception of the plants only fed with NO₃- the Fe concentration in the leaves was not affected by the type of N nutrition. It is therefore assumed that some Fe is immobilized in the leaf tissue by high apoplast pH induced by an increase in the proportion of nitrate in the nutrient solution. Plants fed with Fe (100 μM) showed no chlorosis, regardless of the form of N nutrition and hence regardless of apoplast pH. The Fe concentration in leaves of Fe fed plants was approximately twice those in the leaves not supplied with Fe.     

Iron-deficiency response and expression of genes related to iron homeostasis in poplars

Iron (Fe) deficiency is a serious agricultural problem, especially in calcareous soils, which are distributed worldwide. Poplar trees are an important biomass plant, and overcoming Fe deficiency in poplars will increase biomass productivity worldwide. The poplar Fe-deficiency response and the genes involved in poplar Fe homeostasis remain largely unknown. To identify these genes and processes, we cultivated poplar plants under Fe-deficient conditions, both in calcareous soil and hydroponically, and analyzed their growth rates, leaf Soil and Plant Analyzer Development (SPAD) values, and metal concentrations. The data clearly showed that poplars have notable growth defects in both calcareous soil and a Fe-deficient hydroponic culture. They exhibited serious chlorosis of young leaves after 3 weeks of Fe-deficient hydroponic culture. The Fe concentrations in old leaves with high SPAD values were markedly lower in Fe-deficient poplars, suggesting that poplars may have good translocation capability from old to new leaves. The Zn concentration in new leaves increased in Fe-deficient poplars. The pH of the hydroponic solution decreased in the Fe-deficient culture compared to the Fe-sufficient culture. This finding shows that poplars may be able to adjust the pH of a culture solution to better take up Fe. We also analyzed the expression of Fe homeostasis-related genes in the roots and leaves of Fe-sufficient and Fe-deficient poplars. Our results demonstrate that PtIRT1, PtNAS2, PtFRO2, PtFRO5, and PtFIT were induced in Fe-deficient roots. PtYSL2 and PtNAS4 were induced in Fe-deficient leaves. PtYSL3 was induced in both Fe-deficient leaves and roots. These genes may be involved in the Fe uptake and/or translocation mechanisms in poplars under Fe-deficient conditions. Our results will increase a better understanding of the Fe-deficiency response of poplars and hence improve the breeding of Fe-deficiency-tolerant poplars for improved biomass production, the greening of high pH soils, and combatting global warming.     

Differential manganese tolerances of cotton genotypes in nutrient solution

Cotton genotypes [Gossypium hirsutum (L.)] C‐310–73,‐307 (307) and C‐Sgl, 70–517 (517), shown previously to differ in tolerance to an acid (pH 5.1), high manganese (Mn) Grenada soil from Arkansas, were grown in nutrient solutions containing variable concentrations of excess Mn to confirm and characterize their postulated differences in Mn tolerance. Based on crinkle leaf symptoms and leaf dry weights, the 307 genotype was significantly more tolerant than 517 to 4, 8, or 16 mg Mn/L at a maintained pH of 4.6 (Experiment 1) and also to 4 or 8 mg Mn/L at an initial pH of 5.0, not subsequently adjusted (Experiment 2). In Experiment 1, the relative leaf dry weight (wt. with no Mn/wt. with 8 mg Mn/L × 100) was 94% for genotype 307 and only 27% for 517. In Experiment 2, the corresponding relative leaf weights were 75% and 26% for 307 and 517, respectively. Plant analytical results indicated that the 307 genotype tolerates a higher concentration of Mn in its leaves than does 517. This failure to correlate Mn tolerance with Mn concentrations in plant shoots agrees with previous findings when these two genotypes were grown in acid Grenada soil. Iron (Fe) concentrations, Fe/Mn ratios, and magnesium (Mg) concentrations were higher in the Mn‐tolerant 307 than in the Mn‐sensitive 517, but concentrations of phosphorus (P), potassium (K), calcium (Ca), copper (Cu), and zinc (Zn) were not related to Mn tolerance. Because differential Mn tolerance in these two genotypes is associated with differential internal tolerance to excess Mn, rather than differential Mn uptake, studies are needed to determine the chemical forms of Mn in tolerant and sensitive plants whose leaves contain comparable concentrations of total Mn. Because both Mn and Fe (closely related elements in the Mn toxicity syndrome) have spin resonances, electron paramagnetic resonance (EPR) offers promise in attacking the problem of differential Mn tolerance in plants.