Influence of micronutrient and phosphorous levels and chelator to iron ratio on growth,chlorosis, and nutrition of bluecrop highbush blueberries

‘Bluecrop’ blueberry plants were exposed to 2×2×2 factorial treatments of high and low phosphate and micronutrients (Cu, Zn, Mn, and B) and excess or stoichiometric concentrations of a chelator (EDDHA) added to Fe(NO₃), in pH 6.8 solution cultures. The effects on growth, Fe chlorosis and overall nutrition were accessed. Phosphorous was applied at 20 (low) or 400 (high) μM levels, micronutrients at low or high levels and either a 1:1 or 10:1 ratio of chelator to Fe concentration. Plants grown in excess chelator and low micronutrient supply grew normally. Plants grown in all high micronutrient solutions were chlorotic after 34 days. Plants in low micronutrient and stochiometric chelator to Fe ratio solutions were also chlorotic.

Foliar Fe was not a good indicator of Fe chlorosis development. High Cu levels in roots grown in high micronutrients without excess chelator may have been a causative factor in Fe chlorosis development, but not in reducing foliar Fe levels. There was no indication that excess chelator facilitated Fe transport as has been reported for other crops. However, this work demonstrates that highbush blueberry has an effective ability to absorb Fe from strong Fe chelates and remain non‐chlorotic even at high solution pH levels under an all nitrate‐nitrogen regime. Chemical name used: EDDHA‐ethylenediaminedi‐o‐hydroxyphenlyacetic acid.     

INFLUENCE OF ELEVATED PHOSPHORUS LEVELS IN NUTRIENT SOLUTION ON MICRONUTRIENT UPTAKE AND DEFICIENCY SYMPTOM DEVELOPMENT IN STRAWBERRY CULTURED WITH FERTIGATION SYSTEM

The relationship between the total amount of micronutrients absorbed by the above-ground plant tissue and the occurrence of visible micronutrient deficiency symptoms in two strawberry cultivars as influenced by elevated phosphorus (P) levels in fertigation solution was investigated. The plants were cultured with a fertilizer solution containing 0, 0.5, 1, 2, 4, or 6 mM P and tissue nutrient content were determined at 120 days after transplanting. Young leaves of the plants grown with nutrient solution P levels higher than 4 mM and 2 mM, respectively, in ‘Keumhyang’ and ‘Seonhong’, developed interveinal chlorosis. Tissue concentrations (mg·kg^?1 dry weight) of metallic micronutrients [iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn)] in both cultivars did not decrease, but the total amount absorbed by the aboveground plant tissue decreased in the treatments in which nutrient deficiencies were observed. These results indicate that total amount of micronutrients is a better indicator of P-induced micronutrient deficiency.     

Fertilization of rabbiteye blueberries grown on a typic paleudult soil

A 6 year field study comparing the effects of 5 fertilizer sources applied at 4 levels to 3 rabbiteye blueberry (Vaccinium ashei Reade) cultivars was established on a Typic paleudult soil in southern Misssssippi. Fertilizer sources had little influence on plant height, vigor, chlorosis, or fruit yield. The first year, ‘Tifblue’ was lowest in vigor and fruit yield, but after 4 growing seasons, had the highest plant height and fruit yields. Chlorosis symptoms were more prevalent at the highest fertilization rate, in the cultivar ‘Woodard’, and with Ca(NO₃)₂ fertilizer. During the first 5 years, fruit yields increased as fertilization levels increased from 0 to 5.9 g N/plant but additional fertilization did not influence yields There were no differences in plant vigor due to cultivars but the highest rate of fertilization decreased vigor. The cultivar X fertilization rate interaction was significant for plant height in 1983 and for fruit yields in 1984 and 1985. ‘Delite’ and ‘Woodard’ plant height increased while height of ‘Tifblue’ decreased as fertilization rates increased from the 0 to 5.9 g N/plant levels; higher rates decreased plant height in all cultivars. In 1984 and 1985 fruit yields of ‘Woodard’ and ‘Delite’ were not influenced by fertilization but yields of ‘Tifblue’ indicated a negative response to increasing fertilizer levels.     

Use of 1,10‐phenanthroline in estimating metabolically active iron in plants

Abstract

If calcifuges are forced to grow on a calcareous soil, they usually develop chlorosis. However, total leaf iron (Fe) does not often correlate well with Fe deficiency symptoms. The extraction of ‘active’ Fe by 1 M HCl or Fe chelators, e.g., 1,10‐phenanthroline, may reflect the relation between chlorosis and Fe‐concentration in the leaves better than total Fe does. Extraction of ‘active’ Fe from leaves of wild plants by 1,10‐phenanthroline, citric acid and HC1 was compared. The 1,10‐phenanthroline was chosen for further methodological studies. All samples were extracted at indoor light conditions and analyzed by AAS because dark incubation did not influence the oxidation state of Fe and non‐specific light absorbance seemed to be high in colorimetric analysis. Washing of leaf material with H₂O seemed to clean the leaf surfaces equally well as with 0.1 M HCl. Only fresh leaf material was extracted, as pretreatment (freezing or drying) changed the extractability of Fe. An extraction time of 16 h was adequate for the herbaceous plants tested but not for Carex pilulifera, where extracted Fe increased linearly with time. The age of the extractant solution may play a role because 1,10‐phenanthroline had lost part of its chelation capacity after 6 weeks. The ratio of leaf weight:extractant volume did not influence the amount of Fe extracted, provided the same amount of chelator was supplied. The 1,10‐phenanthroline did not interfere with the Fe determination by AAS, and HCl pH 3 as used for the preparation of the extractants had only a marginal influence on Fe extractability compared to 1,10‐phenanthroline at pH 3. To get comparable results the extraction method should be standardized as much as possible. Samples can be stored in the refrigerator for several hours before adding the extractant and the extracts can be stored for a few days or frozen and measured on the same day, with the same instrument setting.     

CHLOROSIS IN WILD PLANTS: IS IT A SIGN OF IRON DEFICIENCY?

ABSTRACT

Chlorosis in crops grown on calcareous soil is mainly due to iron (Fe) deficiency and can be alleviated by leaf application of soluble Fe²⁺ or diluted acids. Whether chlorosis in indigenous plants forced to grow on a calcareous soil is also caused by Fe deficiency has, however, not been demonstrated. Veronica officinalis, a widespread calcifuge plant in Central and Northern Europe, was cultivated in two experiments on acid and calcareous soils. As phosphorus (P) deficiency is one of the major causes of the inability of many calcifuges to grow on calcareous soil we added phosphate to half of the soils. Leaves in pots with the unfertilized and the P-fertilized soil, respectively, were either sprayed with FeSO₄ solution or left unsprayed. Total Fe, P, and manganese (Mn) in leaves and roots and N remaining in the soil after the experiment were determined. In a second experiment, no P was added. Leaves were either sprayed with FeSO₄ or with H₂SO₄ of the same pH as the FeSO₄ solution. Degree of chlorosis and Fe content in leaves were determined. Calcareous soil grown plants suffered from chlorosis, which was even more pronounced in the soils supplied with P. Newly produced leaves were green with Fe spray but leaves that were chlorotic before the onset of spraying did not totally recover. H₂SO₄ spray even increased chlorosis. This demonstrated that chlorosis was due to Fe deficiency. As total leaf Fe was similar on acid and calcareous soil, it was a physiological Fe deficiency, caused by leaf tissue immobilization in a form that was not metabolically “active”. Iron in the leaves was also extracted by 1,10-phenanthroline, an Fe chelator. In both experiments, significant differences between leaves from acid and calcareous soil were found in 1,10-phenanthroline extractable Fe but not in total leaf Fe, when calculated on a dry weight basis. Differences in 1,10-phenanthroline extractable Fe were more pronounced when calculated per unit dry weight than calculated per leaf area, whereas the opposite condition was valid for total leaf Fe.     

SILICON NUTRITION AND PHYTOPHTHORA DRECHSLERI INFECTION EFFECTS ON GROWTH AND MINERAL NUTRIENTS CONCENTRATION,UPTAKE, AND RELATIVE TRANSLOCATION IN HYDROPONIC-GROWN CUCUMBER

A hydroponic experiment was performed to investigate silicon (Si) and Phytophthora drechsleri root rot effects on growth and tissue partitioning of Si, zinc (Zn), iron (Fe), and manganese (Mn) in two cucumber cultivars (Cucumis sativus L. cvs. ‘Dominus’ and ‘Super Dominus’). Root length, plant height, and root fresh weight were significantly decreased by P. drechsleri, which were all significantly alleviated by 1.0 mM Si. Increasing Si level in the nutrient solution was accompanied with its enhanced uptake by cucumbers. Plants infected with P. drechsleri transported lower Mn to shoot than non-infected plants. Influence of P. drechsleri infection on root Fe concentration was dependent on cucumber cultivar while a decrease in root Zn concentration was found in infected cucumbers. Silicon nutrition increased Zn and Fe uptake in both cucumber cultivars. It is suggested that Si nutrition improved the crop growth, particularly under biotic stress, and hereby, increased micronutrients uptake by cucumber.     

IRON EFFICIENCY IN KENTUCKY BLUEGRASS NOT RELATED TO PHYTOSIDEROPHORE RELEASE

Some Kentucky bluegrass (KBG; Poa pratensis L.) is susceptible to iron (Fe)-deficiency chlorosis. Under Fe-deficiency stress, phytosiderophore is produced and released by the roots of many grasses to solubilize soil Fe and enhance uptake. In other species, quantifying phytosiderophore screens for Fe-deficiency resistant cultivars. A hydroponic study was conducted at 1 and 10 μM solution Fe to variously stress ‘Baron’, ‘Award’, ‘Limousine’, and ‘Rugby II’ KBG cultivars. One μM Fe solution produced more Fe-deficiency stress in all cultivars compared to 10 μM, resulting in greater chlorosis and phytosiderophore release but reduced shoot and root Fe concentrations and shoot weight. Of the four cultivars, Baron was the most susceptible to Fe deficiency and exhibited severe Fe chlorosis and low shoot Fe but, surprisingly, produced the most phytosiderophore. These results imply that Fe-deficiency susceptibility in KBG may be less related to phytosiderophore release and more related to inefficient uptake or utilization mechanisms.     

A greenhouse technique for screening Trifolium seedlings for iron‐deficiency chlorosis 1

Susceptible Trifolium plants often exhibit symptoms of iron (Fe)‐deficiency chlorosis when grown on high pH, calcareous soils. A greenhouse method was developed to screen seedlings for Fe‐deficiency chlorosis. ‘Yuchi’ arrowleaf (T. vesiculosum Savi.) and ‘Dixie’ crimson (I. incarnatum L.) clover seedlings were grown in “Super Cell”; Cone‐tainers in six calcareous Texas soils differing in Fe and selected other chemical characteristics. At the fourth trifoliolate leaf stage, chlorosis was induced by saturating the soil for a minimum of 2 weeks. The soils differed in their capacity to induce chlorosis in both clovers. Yuchi was more susceptible than Dixie, showing a higher percentage of chlorosis in five of the six soils. The results indicate that this screening method would be a useful tool for studying Fe‐deficiency chlorosis in Trifolium spp.     

DIFFERENTIAL RESPONSE OF TWO OLIVE CULTIVARS TO EXCESS MANGANESE

The response of three-month-old rooted cuttings of the olive cultivars ‘Picual’ and ‘Koroneiki’ grown in black plastic bags containing perlite as a substrate to excess manganese (Mn) (640 μM) was studied. The rooted cuttings were irrigated with 50% modified Hoagland nutrient solution. At the end of the experimental period, which lasted 130 days, the total fresh and dry weights, as well as the shoot elongation of ‘Picual’ plants were significantly reduced under excess Mn (640 μM), compared to the control plants (2 μM), whereas the growth of ‘Koroneiki’ plants was similar in both Mn treatments. The tolerance index, which is derived from the ratios between the plant growth data of different treatments and the control one, of ‘Picual’ plants to excess Mn was about half of this of ‘Koroneiki’ plants. In both cultivars, the concentrations of Mn in various plant parts (root, basal stem, top stem, basal leaves, top leaves) were significantly increased as Mn concentration in the nutrient solution increased. Furthermore, in the 640 μM Mn treatment, 2 to 2.5-fold greater Mn concentrations were recorded in almost all plant parts of ‘Koroneiki’, than those of ‘Picual’. Similar results were recorded with regard to the total Mn content per plant (‘Koroneiki’ absorbed much more Mn from the nutrient solution than ‘Picual’). On the other hand, excess Mn negatively affected the absorption of iron (Fe), calcium (Ca), magnesium (Mg), phosphorus (P), zinc (Zn), and boron (B), depending on the olive cultivar. In both cultivars, while the Mn use efficiency was significantly decreased under excess Mn conditions, the nutrient use efficiencies of P, Ca, and Fe were significantly increased, compared to the control plants (2 μM Mn). It was also found that excess Mn resulted in a significant increase of stomatal conductance and transpiration rate of both cultivars, whereas the photosynthetic rate was significantly increased only in ‘Koroneiki’. In ‘Picual’, similar photosynthetic rates were recorded in both Mn treatments. The measurement of the various chlorophyll fluorescence parameters, F_v/F_m and F_v/F₀ ratios, revealed that the functional integrity of photosystem II (PSII) of photosynthesis was not affected due to excess Mn, irrespectively of the cultivar. In conclusion, although ‘Koroneiki’ tissues had much higher Mn concentrations than those of ‘Picual’, the parameters related to the growth and photosynthetic performance of plants indicates that the internal tolerance of ‘Koroneiki’ tissues to excess Mn was higher than this of ‘Picual’.     

Elemental leaf content and deficiency symptoms in rabbiteye blueberries: 1. Nitrogen

Rabbiteye blueberries grown in sand culture were subjected to varying levels of N fertilization (0 ‐ 81 mg N/liter) applied in aqueous solution at the rate of 250 ml/plant daily. Essential elements other than N were kept constant. Shoot growth and leaf concentration of N, P, K, Mg, Ca, Mn, Fe, Cu, B, Zn, Co, and Al were determined. Shoot growth and percent leaf N increased with increased N levels. Shoot growth increased little at N fertilization levels of 0 ‐ 9 mg/ liter but increased rapidly at higher rates. N content in leaves followed a quadratic curve, with % N in leaves increasing more rapidly from 0 to 27 mg N/liter than from 27 to 81 mg N/liter fertilization levels. Leaf concentration of K, Ca, Mg, Mn, B, and Ca decreased linearly as N levels increased. Total content of all elements increased as N fertilization increased. Visual N deficiency became increasingly evident as % N content decreased below 1.4% N.

Nitrogen, the most utilized element in plants, is usually the first to become deficient in sandy soils low in nutrient content (1). Rabbiteye blueberries (Vaccinium ashei Reade) are often grown on acidic, sandy, upland coastal plains soils that are low in cation exchange capacity, organic matter content, and available nutrients. In these acidic soils, NH₄N is more available than in neutral soils (2). The NH₄N source appears to be more suitable for blueberry growth, resulting in greater nutrient uptake, plant growth, and % N of leaf tissue than did the NO₃N sources (5,6).

Nitrogen deficiency symptoms in rabbiteye blueberries are characterized by small, yellow and/or red leaves and stunted plants (3). Since young rabbiteye plants are very sensitive to fertilizer, similar chlorosis symptoms (yellowing or reddening of leaves) can be associated with over‐fertilization, possibly due to root damage (7). Cain (2) found that leaves from healthy container‐grown highbush (V. corymbosum L.) blueberry plants contained about 2% N and higher levels of K and Ca than field‐grown plants. Greenhouse and Field studies indicate that leaf N content in rabbiteye blueberries is usually lower, ranging from about 1.5 to 1.8 (3,7,8). Increased N fertilization decreased the nutrient uptake of other essential elements (Ca and Mg) in rabbiteye blueberries (6). In highbush, Popenoe (4) indicated that a depression of P and K might occur under conditions of high N levels.

This study was initiated to ascertain the effect of NH₄N fertilization levels on uptake patterns of essential elements and to determine the relationships of N fertilization, leaf N content, plant growth, and visible deficiency symptoms.     

Comparative investigation on the susceptibility of faba bean (Vicia faba L.) and sunflower (Helianthus annuus L.) to iron chlorosis

Comparative physiological studies on iron (Fe) chlorosis of Vicia faba L. and Helianthus annuus L. were carried out. High internal Fe contents in Vicia cotyledons (16–37 μg) were completely used for plant growth and Fe chlorosis was not inducible by the application of nitrate (with or without bicarbonate). In Helianthus, low quantities of Fe in the seeds (4 μg) were insufficient for normal growth and without Fe in the nutrient solution, Fe chlorosis was obtained in all treatments. This chlorosis was an absolute Fe deficiency. Also, the treatment with 1 μM Fe in the nutrient solution and nitrate (with or without bicarbonate) led to severe chlorotic symptoms associated with low leaf Fe concentrations and high Fe concentrations in the roots. In contrast, Helianthus grown with NH₄NO₃ and 1 μM Fe had green leaves and high leaf Fe concentrations. However, with NO₃ supply (with or without bicarbonate), Fe translocation from the roots to the upper plant parts was restricted and leaves were chlorotic. Chlorotic and green sunflower leaves may have the same Fe concentrations, leaf Fe concentration being dependent on Fe translocation into the leaf at the various pH levels in the nutrient solution. At low external pH levels (controlled conditions) more Fe was translocated into the leaf leading to similar leaf Fe concentrations with higher chlorophyll concentrations (NH₄NO₃) and with lower chlorophyll concentrations (NO₃). This indicates a lower utilization of leaf Fe of NO₃ grown sunflower plants. Utilization of Fe in faba bean leaves is presumably higher than in sunflower leaves. In Vicia xylem sap pH was not affected by nitrate. In contrast, the xylem sap pH in Helianthus was permanently increased by about 0.4 pH units when fed with nitrate (with or without bicarbonate) compared with NH₄NO₃ nutrition. The xylem sap pH is indicative of leaf apoplast pH. From our earlier work (Mengel et al., 1994; Kosegarten und Englisch, 1994) we therefore suppose that in Helianthus, Fe immobilization occurs in the leaf apoplast due to high pH levels when grown with nitrate (with or without bicarbonate).     

Changes in nutritional homeostasis of Poncirus trifoliata and Ceratonia siliqua as a response to different iron levels in nutrient solution

Abstract

Iron (Fe) deficiency is a nutritional disorder in plants. Poncirus trifoliata is susceptible to Fe deficiency, but symptoms of Fe deficiency are rare in Ceratonia siliqua, a slow-growing species. Specimens of the two species were grown in nutrient solutions containing three Fe concentrations: without Fe (0?µM), 1?µM Fe, and either 10?µM Fe (for Ceratonia) or 40?µM Fe (for P. trifoliata). Growth, the degree of chlorosis, the plant mineral composition, and the activity of the root ferric chelate-reductase (FCR) were assessed. Ceratonia plants exposed to 1?µM Fe were efficient at using Fe in the synthesis of chlorophyll. The activity of FCR was enhanced in the total absence of Fe. In Poncirus a low activity of the FCR was observed in plants with no Fe. The balance between micronutrients in the Ceratonia roots was not affected with 1?µM Fe compared with the higher Fe concentration treatments.     

Micronutrient deficiencies in rainfed calcareous soils of Pakistan. I. Iron chlorosis in the peanut plant

Abstract

Peanut (Arachis hypogaea L.) is susceptible to iron (Fe) chlorosis, however, plant analysis diagnostic criteria are lacking for determining the intensity of chlorosis in this crop. As total Fe content is a misleading index of Fe nutritional status of plants, determination of physiologically active Fe fraction (Fe²⁺) is suggested for the purpose. In a nutrient indexing survey of the chlorosis‐affected peanut crop grown in the rainfed Potohar plateau of Pakistan, o‐phenanthroline extractable Fe²⁺ concentration in plants decreased with increasing severity of chlorosis and thus proved an effective technique for determining the intensity of Fe chlorosis. Green plants contained 40.1 to 67.3 mg Fe²⁺/kg, mildly chlorotic 32.1 to 40.0 mg Fe²⁺/kg, moderately chlorotic 28.0 to 32.0 mg Fe²⁺/kg, and severely chlorotic <28.0 mg Fe²⁺/kg. The minimum Fe²⁺ requirement in green plants was estimated to be 40 mg/kg on dry weight basis. In rainfed field experiments on a calcareous Typic Hapludalfs soil, foliar sprays of 1% solution of sequestrene (NaFeEDDHA) proved superior to the foliar sprays of 0.5% FeSO₄.7H₂O in correcting Fe chlorosis in two cultivars of peanut. Maximum increase in pod yield with sequestrene was 42% in cv. BARD‐92 and 27% in cv. BARD‐699 over the respective control yields. Ferrous concentration in plants increased with both the Fe sources, however, a substantial increase was recorded only with sequestrene. As peanut is a low‐input high‐risk rainfed crop, correction of Fe chlorosis by using sequestrene may not be economically feasible. Thus, development and/or screening of peanut varieties tolerant to Fe chlorosis is suggested by employing Fe²⁺ analysis technique.     

RESPONSES OF “NEWHALL” ORANGE TREES TO IRON DEFICIENCY IN HYDROPONICS: EFFECTS ON LEAF CHLOROPHYLL,PHOTOSYNTHETIC EFFICIENCY,AND ROOT FERRIC CHELATE REDUCTASE ACTIVITY

Orange (Citrus sinensis L. Osb. cv. ‘Newhall’) plants grafted on Citrange troyer rootstock were grown in nutrient solution with 0, 5, 10, or 20 μM iron (Fe), with and without calcium carbonate. Calcium carbonate was added in order to mimic the natural conditions in calcareous soils. Leaf chlorophyll concentration was estimated every 3–4 days using the portable instrument SPAD-502 meter. Chlorophyll fluorescence parameters, photosynthetic capacity estimated from oxygen evolution, leaf Fe concentrations, and root tip ferric chelate reductase activity were measured at the end of the experiment. Plants from the 0 and 5 μM Fe treatments showed leaf chlorosis and had decreased leaf chlorophyll concentrations. Leaves of plants grown in the absence of Fe in the solution had smaller rates of oxygen evolution both in the presence and absence of calcium carbonate, compared with plants grown in the presence of 10 μM Fe. In the absence of calcium carbonate the photosystem II efficiency, estimated from fluorescence parameters, was similar in all treatments. A slight decrease in photosystem II efficiency was observed in plants grown without Fe and in the presence of calcium carbonate. A 2.5-fold increase in root tip ferric chelate reductase activity over the control values was found only when plants were grown with low levels of Fe and in the presence of calcium carbonate.     

Effect of Cadmium and Iron on Rice (Oryza Sativa L.) Plant in Chelator-Buffered Nutrient Solution

ABSTRACT

To better understand the mechanisms responsible for differences in uptake and distribution of cadmium (Cd), nutrient-solution experiments were conducted with different varieties of rice (Oryza sativa), ‘Khitish’ and ‘CNRH3’. The plants were grown in a complete nutrient solution with different levels of pCd (-log free Cd⁺² activity) and pFe [-log free iron (Fe⁺²) activity]. The required concentrations of chelating agent and metals were determined using a computerized chemical equilibrium model such as Geochem-PC. Experimental treatments included a combination of four pCd activity levels (0, 7.9, 8.2, and 8.5) applied as Cd (NO₃)₂ 4H₂O, and two pFe activity levels (17.0 and 17.8) applied as FeCl₃. The application of both Cd and Fe in solution culture significantly affected plant growth, yield, and Cd accumulation in plant tissue. In general, yield of rice was decreased by an increase in amount of solution Cd; however, yield response varied among the cultivars. At the 7.9 pCd level, yields of rice cultivars ‘Khitish’ and ‘CNRH3’ were reduced to 69% and 65%, respectively, compared with control plants. Root Cd concentrations ranged from 2.6 mg kg^?1 (control plants) to 505.7 mg kg^?1 and were directly related to solution Cd concentrations. In rice plants, Cd toxicity symptoms resembled Fe chlorosis. Differential tolerance of varieties to phytotoxicity was not readily visible, but a significant interaction of substrate Cd and variety was obtained from dry-matter yields. Significant interactions indicated that response of tissue Cd concentration, plant Cd uptake, and translocation of Cd to the aerial parts were dependent on variety as well as substrate Cd. Uptake of Cd by roots was significantly higher than by shoots. Higher Cd uptake by rice plants decreased the uptake of other beneficial metals.

The effect of Cd and Fe on the rate of phytometallophore release was also studied in the nutrient solution. Among the rice genotypes, ‘Khitish’ was the most sensitive to Cd toxicity. In both genotypes, with the onset of visual Cd-toxicity symptoms, the release of phytometallophore (PM) was enhanced. Among the rice varieties, ‘Khitish’ had the highest rate of PM release. Treatments with the metal ions studied produced a decrease in chlorophyll and enzyme activity. A decrease in concentrations of chlorophyll pigments in the third leaf was observed due to the highest activity level of Cd (pCd 7.9). Activities of enzymes such as peroxidase (POD) and superoxide dismutase (SOD) are altered by toxic amounts of Cd. Changes in enzyme activities occurred at the lowest activity of Cd (pCd 8.5) in solution. Peroxidase activity increased in the third leaf. Results showed that in contrast with growth parameters, the measurements of enzyme activities may be included as early biomarkers in a plant bioassay to assess the phytotoxicity of Cd-contaminated solution on rice plants. Evidence that Cd uptake and translocation are genetically controlled warrants the selection of varieties that assimilate the least Cd and that translocate the least metal to the plant part to be used for human and animal consumption.     

Influence of Plant Phosphorus and Iron Concentrations on Growth of Soybean

Growth responses to phosphorus (P) and iron (Fe) are commonly assessed based on element concentrations to which plants are exposed. Such data offer little insight about responses to the concentration of P and Fe actually accumulated in plants. In this study, soybean (Glycine max Merr., cv. ‘Biloxi’) was grown on nutrient solutions to induce varying P and Fe concentrations in plant tissues. Leaf P and Fe concentrations were correlated at lower concentrations. However, under high P treatments there was an apparent excess of accumulated P based on plant response. These results were interpreted to indicate that these plants could accumulate P in excess of the amount required for normal physiological activity. There appeared to be no excess accumulation of Fe so that correlations between leaf Fe concentration and leaf area and plant mass were significant for all data. Root mass did not correlate significantly with either leaf P or Fe concentration.     

Assessment of Disturbances in Growth and Physiology of Carrot Caused by Chromium Stress

To see the deleterious effects of excess chromium (Cr) on carrot (Daucus carota L.) the cv. ‘Pusa Keshari’ was grown in refined sand under controlled glasshouse conditions with a complete nutrient solution (without Cr) for 48 days. On the 49th day, pots with two plants each were separated into three sets. One set served as a control. In each of the other two sets, Cr was supplied as dichromate at 0.1 and 0.5 mM to the basal nutrient solution. At 0.5 mM Cr toxicity symptoms appeared at d 52 (4 days after Cr supply) as reduction in growth and leaf size and loss of turgor. Old leaves became chlorotic and wilted. Chlorosis intensified and turned necrotic in another few days. These symptoms spread to next upper leaf. The development of chlorosis in leaves was delayed in plants receiving 0.1 mM Cr. At excess Cr (0.5 mM) in carrot, the biomass, concentration of chlorophylls a and b, iron (Fe), sulfur (S), and phosphorus (P) in shoots, and activity of catalase (CAT) in leaves decreased whereas the concentration of Cr and the activity of peroxidase (POX), superoxide dismutase (SOD), ribonuclease (RNAse), and acid phosphatase (A P) in leaves increased.     

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.     

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.     

Distribution and secondary effects of EDDHA in some vegetable species

Tomato (Lycopersicum esculentum), cucumber (Cucumis sativus), pepper (Capsicum annuum), and lettuce (Lactuca sativa) were grown on rockwool or perlite substrate with nutrient solution. Fe was administered as the Fe complex of the chelator ethylenediamine di-(o-hydroxyphenylacetic acid) (EDDHA) or Fe(NH₄)₂(SO₄)₂ in the nutrient solution or as inorganic iron in the substrate. Roots and leaves of plants grown on Fe-EDDHA contained EDDHA in quantities up to 0.27 × the amount of Fe, which is interpreted as an indication of the contribution of passive chelate absorption to Fe uptake. Fruits of tomato and pepper, and leaves of lettuce contained only traces of EDDHA. Breakdown of the chelator in leaves of pepper and tomato is estimated to have been between 0.5 and 2% per day. In tomato fruits, lycopene content was lowered in plants growing on Fe-EDDHA. Cucumber growing on Fe-EDDHA suffered from serious infection by the mildew Sphaerotheca fusca; the plants growing on an inorganic source of iron were resistant. These results exemplify physiological effects of EDDHA other than those directly associated with iron nutrition.