Symptoms Of Zinc Deficiency Research Articles

Cytological and Ultrastructural Evaluations of Zinc Deficiency in Leaves

Zinc deficiency is a widespread nutritional disorder in plants and occurs in both temperate and tropical climates. In spite of its physiological importance, cytological and ultrastructural changes associated with zinc deficiency are lacking, in part because zinc deficiency is difficult to induce. A method was developed to induce zinc deficiency in pecan (Carya illinoinensis (Wangenh.) C. Koch) using hydroponic culture. Zinc deficiency was evaluated in leaves using light and electron microscopy. Zinc deficiency symptoms varied with severity ranging from interveinal mottling, overall chlorosis, necrosis, and marginal curving. Zinc deficient leaves were thinner, and palisade cells were shorter, wider, and had more intercellular spaces than zinc sufficient leaves. Cells in zinc deficient leaves had limited cytoplasmic content and accumulated phenolic compounds in vacuoles. Extensive starch accumulation was observed in chloroplasts. This work represents the first detailed microscopic evaluations of zinc deficiency in leaves, and provides insight on how zinc deficiency affects leaf structure and function.

Breeding Wheat for Zinc Efficiency Improvement in Semi-arid Climate-A Review

Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world. Zinc deficiency is one of the most common deficiencies in soils worldwide. Several plant metabolic processes and biological functions are impaired under Zn deficient conditions. The most visible symptoms of zinc deficiency are a reduction in shoot growth, decrease in leaf size, chlorophyll degeneration and the emergence of whitish-brown necrotic patches on leaves. The genotypes that show the highest percent response to added Zn and are unable to grow well without Zn are defined as being susceptible to Zn deficiency and vice versa. Zinc efficiency is the ability of a plant to grow and produce grain when Zinc availability is low. Breeding cereals with enhanced zinc efficiency can decrease fertilizer dependency, improve seed-ling vigor, increase resistance to abiotic and biotic stress and enhance yield and nutritional value of wheat. A survey of the literature, as well as own experiences, show that there is enough genetic variation in wheat and alien species, particularly rye, for suitable zinc-efficient alleles. Genetic control is fairly simple, making breeding for this trait feasible. Since selection for Zinc efficiency in a breeding program is limited by the high spatial variability of zinc in field sites, better field screening techniques and selection criteria are needed to allow screening of early-generation segregating materials. Zn specific diagnostic methods like reflectance analysis and molecular markers (proteins /DNA markers) could complement the screening of wheat genotypes for zinc efficiency. Breeding wheat for enhanced zinc efficiency and higher grain yield would require concentrating the quantitative trait loci governing these traits in a few agronomic backgrounds through recombination breeding. This literature review paper delves into genetic variability, screening methods, plant breeding options and methodologies and other related issues for improving zinc efficiency in wheat.

STUDIES ON THE EFFECT OF ZINC SUPPLY ON GROWTH AND NUTRIENT UPTAKE IN PECAN

ABSTRACT Zinc (Zn) deficiency is a nutrient disorder observed in pecan (Carya illinoinensis Wangenh. K. Koch) under field conditions, and can cause distorted leaf growth and severe rosetting of shoots. Conducting Zn studies with pecan in the field have been problematic because Zn nutrition is difficult to control. In this study, Zn nutrient disorders were induced in greenhouse-grown pecan seedlings using hydroponic culture. Zinc efficiency was compared in two pecan seedstocks, ‘Stuart’ and ‘Curtis’ by evaluating growth response, nutrient uptake, and leaf nutrient analysis. Zinc deficiency symptoms appeared in plants grown in the absence of Zn after six weeks. Deficiency symptoms were characterized by interveinal mottling, followed by interveinal chlorosis, interveinal necrosis, and marginal curling. Symptoms were confined to the youngest most distal three to five leaves. Differences in Zn efficiency between the two seedstock were observed. “Stuart” exhibited more severe deficiency ratings than “Curtis”. Zinc supply also had a differential effect on the foliar concentration and content of Zn and other nutrient. “Stuart” seedstocks grown under minus Zn vs. plus Zn conditions exhibited significantly higher foliar concentration of phosphorus (P), calcium (Ca), magnesium (Mg), and copper (Cu), while “Curtis” leaves contained significantly higher manganese (Mn) and lower sulfur (S). Results of this study concur with the observed frequency of Zn deficiencies of the cultivars in the field, i.e., “Stuart” shows Zn deficiency more frequently then “Curtis”. This study verifies that in pecan, there are genotypic differences in Zn efficiency, and that hydroponic culture can be utilized for screening and selection.

Secretory Function of the Salivary Gland in Patients with Taste Disorders or Xerostomia: Correlation with Zinc Deficiency

A notable proportion of patients with taste disorders complain of xerostomia and when zinc is prescribed the xerostomia is often improved in conjunction with the taste disorder. To study the relationship between taste disorders, zinc deficiency and xerostomia, we measured salivary gland function and zinc levels in 93 patients with hypogeusia and/or xerostomia and 60 patients with unilateral acute peripheral facial palsy who served as controls. We then prescribed zinc for patients with low serum zinc levels and evaluated xerostomia and taste sensation after 6 months of this treatment. The salivary gland secretory ratio (SGSR), determined by dynamic salivary 99mTc scintigraphy, was found to be an objective measure of salivary gland function and was reduced in patients with xerostomia. Patients with salivary gland dysfunction also had abnormal morphology of the papillae of the tongue. No significant relation was found between the severity of taste disorders and SGSR values, but low SGSR values were found in patients with zinc deficiency. Patients with taste disorders and/or xerostomia who were treated with zinc had relief of symptoms at 6 months, indicating that both taste disorders and xerostomia are among the symptoms of zinc deficiency.

Influence of variable zinc on yield, oil content, and physiology of sunflower

ABSTRACT Sunflower (Helianthus annuus L.) cv. Jwala Mukhi was grown until maturity in refined sand at variable levels of zinc ranging from acute deficiency to excess (0.00065 to 65 mg L−1). Both low (<0.065 mg L−1) and high (>0.065 mg L−1) zinc depressed the growth of sunflower. Foliar symptoms of zinc deficiency appeared on mature middle and old leaves of plants at 0.00065 and 0.0065 mg Zn L−1 as interveinal chlorosis and fading of green color from margins and apices. Later, leaf apices of the affected leaves turned necrotic and dry. Biomass, capitulum size, seed number, seed weight, concentration of chlorophylls a and b, and soluble proteins were maximum at 0.065 mg Zn L−1 (adequate), and were lowered significantly in both deficiency and excess of zinc. The effect of excess zinc (65 mg Zn L−1) on these parameters was more pronounced. An increase in zinc from low (0.00065 mg L−1) to high (65 mg Zn L−1) increased the activity of carbonic anhydrase (up to 6.5 mg Zn L−1) and decreased that of acid phosphatase in sunflower leaves. Zinc deficiency lowered the concentration of zinc and increased that of phosphorus in leaves. In sunflower seeds, the oil content was highest (23.4%) at 0.65 mg Zn L−1 and was reduced more by Zn excess than deficiency. In leaves, tissue Zn concentrations associated with deficiency, threshold of deficiency, threshold of toxicity and toxicity were 20, 30, 190, and 240 μg g−1 on a dry matter basis, respectively.

Occurrence of Fusarium‐produced naphthazarins in citrus trees and sensitivity of rootstocks to isomarticin in relation to citrus blight

Fusarium solani, the causal fungus of root and crown rot of citrus, produces naphthazarin toxins that were shown to be toxic to citrus plants. It was found that citrus trees in South Africa had varying levels of naphthazarins in their xylem. Significantly higher concentrations of these toxins were detected in trees with blight symptoms than in symptomless trees. Citrus seedlings grown in hydroponic culture containing isomarticin showed inhibition of growth, shortening of roots and accumulation of zinc in the trunk wood. Zinc deficiency symptoms were also observed on certain rootstocks. A procedural ranking of rootstocks indicated that trees with observed tolerance to blight in the field generally had higher tolerance to isomarticin in hydroponic culture, whereas trees susceptible to blight were more sensitive to the toxin. These findings indicate that Fusarium‐produced isomarticin is involved in the induction of some of the symptoms associated with citrus blight syndrome.

Differences in shoot growth and zinc concentration of 164 bread wheat genotypes in a zinc‐deficient calcareous soil

A greenhouse experiment was carried out to study severity of the zinc (Zn) deficiency symptoms on leaves, shoot dry weight and shoot content and concentration of Zn in 164 winter type bread wheat genotypes (Triticunt aestivum L.) grown in a Zn‐deficient calcareous soil with (+Zn=10 mg Zn kg−1 soil) and without (‐Zn) Zn supply for 45 days. Tolerance of the genotypes to Zn deficiency was ranked based on the relative shoot growth (Zn efficiency ratio), calculated as the ratio of the shoot dry weight produced under Zn deficiency to that produced under adequate Zn supply. There was a substantial difference in genotypic tolerance to Zn deficiency. Among the 164 genotypes, 108 genotypes had severe visible symptoms of Zn deficiency (whitish‐brown necrotic patches) on leaves, while in 25 genotypes Zn deficiency symptoms were slight or absent, and the remaining genotypes (e.g., 31 genotypes) showed mild deficiency symptoms. Generally, the genotypes with higher tolerance to Zn deficiency originated from Balkan countries and Turkey, while genotypes originating from the breeding programs in the Great Plains of the United States were mostly sensitive to Zn deficiency. Among the 164 wheat genotypes, Zn efficiency ratio varied from 0.33 to 0.77. The differences in tolerance to Zn deficiency were totally independent of shoot Zn concentrations, but showed a close relationship to the total amount (content) of Zn per shoot. The absolute shoot growth of the genotypes under Zn deficiency corresponded very well with the differences in tolerance to Zn deficiency. Under adequate Zn supply, the 10 most Zn‐ inefficient genotypes and the 10 most Zn‐efficient genotypes were very similar in their shoot dry weight. However, under Zn deficiency, shoot dry weight of the Zn‐efficient genotypes was, on average, 1.6‐fold higher compared to the Zn‐inefficient genotypes. The results of this study show large, exploitable genotypic variation for tolerance to Zn deficiency in bread wheat. Based on this data, total amount of Zn per shoot, absolute shoot growth under Zn deficiency, and relative shoot growth can be used as reliable plant parameters for assessing genotypic variation in tolerance to Zn deficiency in bread wheat.

The Role of Zinc in Growth and Cell Proliferation

The inhibition of growth is a cardinal symptom of zinc deficiency. In animals fed a zinc-inadequate diet, both food intake and growth are reduced within 4-5 d. Despite the concomitant reduction in food intake and growth, reduced energy intake is not the limiting factor in growth, because force-feeding a zinc-inadequate diet to animals fails to maintain growth. Hence, food intake and growth appear to be regulated by zinc through independent, although well coordinated, mechanisms. Despite the long-term study of zinc metabolism, the first limiting role of zinc in cell proliferation remains undefined. Zinc participates in the regulation of cell proliferation in several ways; it is essential to enzyme systems that influence cell division and proliferation. Removing zinc from the extracellular milieu results in decreased activity of deoxythymidine kinase and reduced levels of adenosine(5')tetraphosphate(5')-adenosine. Hence, zinc may directly regulate DNA synthesis through these systems. Zinc also influences hormonal regulation of cell division. Specifically, the pituitary growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis is responsive to zinc status. Both increased and decreased circulating concentrations of GH have been observed in zinc deficiency, although circulating IGF-I concentrations are consistently decreased. However, growth failure is not reversed by maintaining either GH or IGF-I levels through exogenous administration, which suggests the defect occurs in hormone signaling. Zinc appears to be essential for IGF-I induction of cell proliferation; the site of regulation is postreceptor binding. Overall, the evidence suggests that reduced zinc availability affects membrane signaling systems and intracellular second messengers that coordinate cell proliferation in response to IGF-I.

Growth and nutrition of Betula pendula at different relative supply rates of zinc.

Small birch plants (Betula pendula Roth) were cultivated in a hydroponic spray solution where the relative growth rate (R(G); day(-1)) was controlled by the relative supply rate of zinc (R(Zn); day(-1)). After an adjustment phase to steady-state growth, R(G) equaled R(Zn). The R(Zn) treatments were 0.05, 0.125 and 0.20 day(-1) with free access to all other nutrients. In an additional treatment, there was free access to all nutrients, including zinc (FA treatment). The pH of the nutrient solution was approximately 4.5 and conductivity was 100 &mgr;S cm(-1). The duration of each treatment depended on R(Zn) and ranged from 4 (FA treatment) to 10 weeks (at R(Zn) = 0.05 day(-1)). The plants showed persistent and typical zinc-deficiency symptoms at steady-state growth when R(G) was 0.05 and 0.125 day(-1), whereas there were few symptoms when R(G) was 0.2 day(-1). The Zn concentration of the plants ranged from 8 (at R(Zn) = 0.05 day(-1)) to 21 &mgr;g g(DM) (-1) (DM = dry mass) (at R(Zn) = 0.2 day(-1)) and was approximately 42 &mgr;g g(DM) (-1) in the FA treatment. Uptake rates of Zn, calculated per root growth rate (&mgr;mol g(DM, root) (-1)), were about 2.8 times higher at R(Zn) = 0.20 day(-1) than at R(Zn)= 0.05 day(-1). The root and stem biomass fractions were approximately constant at all supply rates of Zn, whereas the leaf biomass fraction tended to increase with increasing supply rate of Zn. Net assimilation rate was constant from FA to an R(Zn) of 0.125 day(-1) but decreased by a factor of about 2 at R(Zn) = 0.05 day(-1). Leaf area ratio and specific leaf area were smaller at low supply rates of zinc than at high supply rates.

Citrus Blight Found in Yucatan, Mexico.

Citrus blight, a serious tree decline problem of unknown cause in humid citrus-growing areas such as Florida and Louisiana, South America, South Africa, and the Caribbean, has never been reported from Mexico. Citrus blight has no reliable visual symptoms, and physical and chemical tests have to be used for diagnosis. We used water injection into the trunk (2), zinc and potassium analysis of the outer trunk wood (3), and an immunological test for specific blight proteins in the leaves (1). Low uptake when water is injected into the trunk, and high zinc and potassium in the wood, compared with healthy trees, are characteristic of citrus blight (3). Water injection tests and wood analysis of four healthy and four declining trees in the Dzan, Yucatan, Mexico, area in August 1995, showed highly significant differences in water uptake (healthy trees 44.3 ml/min, declining trees 1.0 ml/min), little difference in wood zinc (healthy 2.8 μg/g, declining 3.0 μg/g) and 39% more potassium in the wood (healthy 0.147%, declining 0.204%). No leaf protein tests were done at this location. Tests on eight declining and five healthy trees in Seye, Yucatan, Mexico, in June 1996, showed significant (P = 0.01 to 0.05) differences in water uptake (healthy 12.9 ml/min, declining 0.6 ml/min), in wood zinc (healthy 2.0 μg/g, declining 7.0 μg/g) and potassium in the wood (healthy 0.156%, declining 0.251%). Leaf samples from all eight declining trees were positive for blight in a specific protein test (1). The visual symptoms of all declining trees tested were the same as those of blight-affected trees in Florida and Cuba: zinc deficiency symptoms in the leaves, thin foliage, wilt, and sprouting from the trunk and the main branches. The reasons for the lack of earlier reports of citrus blight from Mexico are apparently climatic and rootstock related. Many of Mexico's citrus-producing areas are dry and blight does not occur in dry areas such as the Mediterranean countries and California. Most of Mexico's citrus is grown on sour orange (Citrus aurantium L.) rootstock that is highly resistant to citrus blight, but very susceptible to tristeza virus disease. In response to warnings that tristeza disease might appear in Yucatan, growers planted Valencia orange (C. sinensis (L.) Osbeck) on Cleopatra mandarin (C. reticulata Blanco) rootstock in Dzan and on Volkamer lemon (C. limon (L.) N. L. Burm.) in Seye, both highly susceptible to citrus blight (4). Changes in rootstock to avoid one disease led to problems with another.

2005 Neural substrates for the reception of odor of estrous females that provokes noncontact penile erection in the rat

Zinc deficiency causes various symptoms including taste disorders. In the present study, changes in expression of c-Fos immunoreactivity in neurons of the parabrachial nucleus (PBN), one of the relay nuclei for transmission of gustatory information, after bitter stimulation to the dorsal surface of the tongue were examined in zinc-deficient rats. Experimental zinc-deficient animals were created by feeding a low-zinc diet for 4 weeks, and showed the following symptoms of zinc deficiency: low body weight, low serum zinc content and behavioral changes to avoid bitter stimulation. In normal control animals, intraoral application of 1 mM quinine caused increased numbers of c-Fos-immunoreactive (c-Fos-IR) neurons in the external lateral subnucleus and external medial subnucleus of the PBN (elPBN and emPBN, respectively) compared with application of distilled water. However, in the zinc-deficient animals, the numbers of c-Fos-IR neurons in the elPBN and emPBN did not differ significantly between application of quinine and distilled water. After feeding the zinc-deficient animals a normal diet for 4 weeks, the symptoms of zinc deficiency recovered, and the expression of c-Fos-IR neurons following intraoral bitter stimulation became identical to that in the normal control animals. The present results indicate that dietary zinc deficiency causes alterations to neuronal activities in the gustatory neural circuit, and that these neuronal alterations can be reversed by changing to a normal diet.

Zinc Stores in Chickens Delay the Onset of Zinc Deficiency Symptoms

Three chick assays were conducted to evaluate Zn depletion rates in whole body and various tissues. In Assay 1, chicks fed a corn-soybean meal diet containing 1,037 mg Zn/kg had twice as much Zn in intestine and bone and 50% more Zn in liver and whole body than chicks fed 37 mg Zn/kg (P < .01). In Assay 2, the minimum Zn requirement for growth of chicks consuming a chemically defined, amino acid diet was 10.6 mg Zn/kg. In Assay 3, chicks were fed the chemically defined diet containing either 300 or 10.6 mg Zn/kg during an 8-d pretest period, after which they were fed either 0 or 10.6 mg Zn/kg for 9 d. Tissue Zn concentrations were determined on Days 0, 1, 2, 3, 4, 5, 7, and 9 of the test period. Following the pretest period, Zn was higher in the liver, tibia, and small intestine, but not in muscle, of chicks fed 300 mg Zn/kg than of those fed 10.6 mg Zn/kg (P < .01). Growth of chicks switched from 10.6 to 0 mg Zn/kg was less than for chicks maintained on 10.6 mg Zn/kg by Day 5 (P < .05), whereas chicks switched from 300 to 0 mg Zn/kg did not display a growth depression relative to the control until Day 8 (P < .05). Zinc that accumulated in the liver and small intestine of chicks fed the 300 to 0 Zn regimen declined until Day 3 of the test period, whereas tibia Zn decreased until Day 8. Chicks fed the 10.6 to 0 regimen did not display a substantial decrease in small intestine, liver, or tibia Zn. The data confirm that Zn can accumulate in bone, liver, and intestine and can subsequently be released for use during a period of Zn deficiency. The data also indicate that chicks fed a diet containing the minimum requirement of Zn cannot accumulate reserves of Zn that become available for use during a subsequent period of Zn depletion.

Zinc: health effects and research priorities for the 1990s.

This review critically summarizes the literature on the spectrum of health effects of zinc status, ranging from symptoms of zinc deficiency to excess exposure. Studies on zinc intake are reviewed in relation to optimum requirements as a function of age and sex. Current knowledge on the biochemical properties of zinc which are critical to the essential role of this metal in biological systems is summarized. Dietary and physiological factors influencing the bioavailability and utilization of zinc are considered with special attention to interactions with iron and copper status. The effects of zinc deficiency and toxicity are reviewed with respect to specific organs, immunological and reproductive function, and genotoxicity and carcinogenicity. Finally, key questions are identified where research is needed, such as the risks to human health of altered environmental distribution of zinc, assessment of zinc status in humans, effects of zinc status in relation to other essential metals on immune function, reproduction, neurological function, and the cardiovascular system, and mechanistic studies to further elucidate the biological effects of zinc at the molecular level.

Application of chelator-buffered nutrient solution technique in studies on zinc nutrition in rice plant (Oryza sativa L.)

It has been difficult to impose different degrees of Zn deficiency on Poaceae species in nutrient solution because most chelators which would control Zn to low activities also bind Fe3+ so strongly that Poaceae species cannot obtain adequate Fe. Recently, a method has been developed to provide buffered Fe2+ at levels adequate for rice using Ferrozine (FZ), and use of other chelators to buffer the other micronutrient cations. The use of Fe2+ buffered with FZ in nutrient solutions in which Zn is buffered with HEDTA or DTPA was evaluated for study of Zn deficiency in rice compared to a conventional nutrient solution technique. The results showed that growth of rice plants in FZ+HEDTA-buffered nutrient solution was similar to that in the conventional nutrient solution. Severe zinc deficiency symptoms were observed in 28-day-old rice seedlings cultured with HEDTA-buffered nutrient solution at Zn2+ activities < 10-10.6 M. With increasing free Zn2+ activities, concentrations of Zn, Fe, Cu, and Mn in shoots and roots were quite similar for the FZ+HEDTA-buffered nutrient solution and the conventional nutrient solution techniques. The percentages of water soluble Zn, Fe, Cu and Mn in shoots with HEDTA-buffered nutrient solution were also similar to those with the conventional solution. However, with DTPA-buffered nutrient solution, the rice seedlings suffered severe Fe deficiency; adding more FeFZ3 corrected the Fe-chlorosis but shifted microelement buffering. Further, much higher total Zn concentrations are required to provide adequate Zn2+ in DTPA-buffered solutions, and the contents of Mn and Cu in shoots and roots cultured with DTPA-buffered solutions were much higher than those with the conventional or HEDTA-buffered solutions. In conclusion, DTPA-buffered nutrient solutions are not suitable but the FZ/HEDTA-buffered nutrient solution technique can be used to evaluate genotypic differences in zinc efficiency in rice.

Secretory function of the salivary gland in patients with taste disorders--correlations between zinc deficiency and secretory functions of the salivary glands

Not a few patients with taste disorders complain of xerostomia as another subjective symptom. When zinc is subscribed, the xerostomia is often reduced in conjunction with the taste disorders. In this study, therefore, a trial was made to detect xerostomia objectively by determining the function of salivary glandular secretion, and then relationship between zinc deficiency and the xerostomia was examined. Ninety three patients who complained of hypogeusia and/or xerostomia, 27 males and 66 females ranging from 39 to 87 years of age, were subjected to dynamic salivary scintigraphy using 99mTc-pertechnetate. Control data were obtained from 60 patients with unilateral acute peripheral facial palsy. The conclusions obtained were as follows: 1. The normal range of the salivary glandular secretory ratio (S.G.S.R.) was determined from the dynamic salivary scintigraphy using 99mTc-pertechnetate. 2. The xerostomia appeared to be detectable by the above method. 3. Dysfunctional salivary glandular secretion seemed to be associated with abnormal morphology of the papillae of the tongue. 4. No significant relation was found between the severity of taste disorders and the values of S.G.S.R. 5. In terms of the mean value, low values of S.G.S.R. were observed to coincide with zinc deficiency. 6. From the results of zinc treatment, we demonstrated correlations between taste disorders and xerostomia, both of which are among the symptoms of zinc deficiency.

Enhancement of zinc utilization from phytate-rich soy protein isolate by microbial phytase.

A study with three groups, each with 11 male, individually housed albino rats (initial average weight = 50 g) was undertaken to examine the effect of microbial phytase (added to a diet containing phytate) on the availability of zinc. The rats were fed diets on the basis of soy protein isolate and corn starch over a 3-week period. All diets contained 15-16 mg Zn/kg diet and 0.40% PA. Thus, molar PA:Zn-ratios of 26:1 were obtained. Group I (control) was fed the phytase-free basal diet. In groups II (pair-fed to group I) and III, 1,000 U of microbial phytase (Aspergillus niger var. van tighem) per kg diet were added. Some rats fed the phytase-free basal diet (control) showed typical symptoms of zinc deficiency, including cyclic changes in food intake, anorexia and partial alopecia. By the addition of 1,000 U microbial phytase the apparent absorption of zinc (percent of intake) significantly increased from 33% (control) to 63% (1,000 U, pair-fed) and 66% (1,000 U, ad lib.). Similar positive effects of the phytase-supplementation were observed for three zinc status parameters in plasma, zinc-concentration, percent unsaturated zinc-binding capacity, activity of alkaline phosphatase and the zinc-concentration in femur and testes. The present study shows that an addition of microbial phytase to phytate-rich diets based on soy protein isolate considerably improves the availability of zinc in growing rats.

Assessment of zinc status in juvenile Atlantic salmon ( Salmo salar) by measurement of whole body and tissue levels of zinc

Duplicate groups of 40 g Atlantic salmon were fed dry pelleted diets based on cod muscle meal as a protein source for 8 weeks. The basal diet contained 17 mg Zn/kg to which 0, 10, 20, 40 or 80 mg Zn/kg diet, respectively, were added as ZnSO 4·7H 2O. After 8 weeks, 15 fish from each dietary treatment were marked and then they were fed the basal diet for another 4 weeks. Fish were sampled after 2, 4, 8 and 12 weeks. Blood samples were withdrawn and serum was analyzed for zinc concentration and alkaline phosphatase (AP) activity. Liver, kidney, vertebrae and intestine were removed from ten fish in each dietary treatment. A further ten fish were used for whole body mineral analyses. There were no significant differences in growth due to different dietary zinc concentrations and this, together with data on alkaline phosphatase and iron levels, showed that the basal diets contained sufficient zinc to prevent overt zinc deficiency symptoms. Zinc concentrations in the whole body and tissues, however, were significantly influenced by dietary zinc level. On the basis of the dietary zinc concentration required to maintain whole body zinc and serum zinc concentrations within the normal range, it was concluded that the dietary zinc requirement of juvenile Atlantic salmon is between 37 and 67 mg Zn/kg dry diet under our test conditions. Hence, until more data are available, juvenile Atlantic salmon diets based almost entirely on marine fish protein should contain > 67 mg Zn/kg dry diet.

MACROPHYLLA DECLINE: A NEWLY DESCRIBED DISORDER IN CITRUS

Macrophylla decline was observed primarily in lemons on the macrophylla rootstock (Citrus macrophylla, Wester). This disorder is characterized by foliar zinc deficiency symptoms with zinc accumulation in trunk phloem above the bud union. Trees show symptoms of twig dieback and are less thrifty in appearance compared to the same cultivars on other rootstocks. These characteristics are very similar to a citrus disorder of humid citrus production regions, citrus blight. Citrus blight affects the more vigorous rootstocks (a characteristic of Macrophylla) such as the extremely blight susceptible rough lemon rootstock. In the humid regions, macrophylla is considered somewhat susceptible to blight. Experiments are currently underway to assess the water conductivity of xylem in trees on macrophylla and to screen for the presence of citrus blight specific proteins.

Influence of zinc on the growth, distribution of elements, and metabolism of one‐year old American ginseng plants

Abstract Using a water culture technique, 0.05 ppm zinc (Zn) was found to be the critical deficiency concentraction for one‐year American ginseng (Panax quinquefolium L) plants, 0.3 ppm was optimum, 0.5 ppm the critical Zn‐toxicity concentration, and 10 ppm the concentration when severe toxicity occurs. Therefore, the optimum Zn concentration for the growth of American ginseng plants was between 0.1 ppm ‐ 0.3 ppm. Zinc deficiency symptoms of one‐year old American ginseng plants were indicated by the inhabition of root growth, with little fibrous root development, and smaller leaves compared to normal leaves. The symptoms of toxicity were also indicated by the inhibition of root growth, and when seedlings were suffering from an acute toxicity, no fibrous roots appeared, and eventually the roots yellowed and leaves grew slowly or even entirely ceased to grow, the final result being very small leaves which are also chlorotic. Zinc maintained within the 0.1 ppm to 0.3 ppm sufficiency range promoted the synthe...

Effect of Zinc Deficiency on Proton Fluxes in Plasma Membrane-Enriched Vesicles Isolated from Bean Roots

Plasma membrane-enriched vesicles were isolated by density gradient centrifugation from roots of zinc-sufficient and zinc-deficient bean (Phaseolus vulgaris L. cv. Prelude) plants. The two populations of vesicles had similar activities of specific membrane marker enzymes and ATP hydrolysis and were competent for proton transport. However, vesicles from zinc-deficient roots showed lower rates of ATP-dependent intravesicular acidification and increases in passive permeability to protons as well as in the rate of dissipation of a non-metabolic transmembrane pH gradient. The decrease of the rate of proton accumulation in isolated vesicles closely paralleled the increase in potassium leakage from intact roots and the appearance of visual zinc deficiency symptoms in the shoots. Re-supply of zinc to deficient plants for 24 h promoted shoot growth, reduced potassium leakage from roots and led to partial recovery of the proton accumulation capacity and to a decrease in passive permeability to protons in isolated vesicles. The results obtained with isolated vesicles confirm the previously observed 'in vivo' effects of zinc deficiency and are consistent with the idea that an alteration of plasma membrane lipids leads to an increase in permeability and an impairment in trans plasma membrane proton gradient.