Zn Efficiency Research Articles

Crescimento diferencial e eficiência de uso em zinco de cultivares de milho submetidos a doses de zinco em um Latossolo Vermelho

This work was carried out in a greenhouse to evaluate the growth and Zn efficiency of maize cultivars of different technologies submitted to Zn rates, relating the plants’ response to Zn level in both soil and plant. The experiment had a factorial arrangement 4 x 3 [four Zn rates (0, 1, 2, and 3 mg kg-1) and three cultivars (variety Al-Manduri, double-cross hybrid C 701, and triple-cross hybrid P 3041)] in a completely randomized design. Hybrids C 701 and P 3041 needed higher Zn rates than the Al-Manduri variety to express maximum dry matter production of the plant shoot, which was associated with different requirements of each cultivar for available Zn in soil. On the other hand, Al-Manduri and P 3041 cultivars presented a higher Zn use efficiency than the C 701 cultivar. The hybrids had Zn critical level higher than the variety, both in soil and plant.

Characterization of natural variation for zinc, iron and manganese accumulation and zinc exposure response in Brassica rapa L.

Brassica rapa L. is an important vegetable crop in eastern Asia. The objective of this study was to investigate the genetic variation in leaf Zn, Fe and Mn accumulation, Zn toxicity tolerance and Zn efficiency in B. rapa. In total 188 accessions were screened for their Zn-related characteristics in hydroponic culture. In experiment 1, mineral assays on 111 accessions grown under sufficient Zn supply (2 μM ZnSO4) revealed a variation range of 23.2–155.9 μg g−1 dry weight (d. wt.) for Zn, 60.3–350.1 μg g−1 d. wt. for Fe and 20.9–53.3 μg g−1 d. wt. for the Mn concentration in shoot. The investigation of tolerance to excessive Zn (800 μM ZnSO4) on 158 accessions, by using visual toxicity symptom parameters (TSPs), identified different levels of tolerance in B. rapa. In experiment 2, a selected sub-set of accessions from experiment 1 was characterized in more detail for their mineral accumulation and tolerance to excessive Zn supply (100 μM and 300 μM ZnSO4). In this experiment Zn tolerance (ZT) determined by relative root or shoot dry biomass varied about 2-fold. The same six accessions were also examined for Zn efficiency, determined as relative growth under 0 μM ZnSO4 compared to 2 μM ZnSO4. Zn efficiency varied 1.8-fold based on shoot dry biomass and 2.6-fold variation based on root dry biomass. Zn accumulation was strongly correlated with Mn and Fe accumulation both under sufficient and deficient Zn supply. In conclusion, there is substantial variation for Zn accumulation, Zn toxicity tolerance and Zn efficiency in Brassica rapa L., which would allow selective breeding for these traits.

Responses of Wheat Genotypes to Zinc Fertilization Under Saline Soil Conditions

ABSTRACT A greenhouse experiment with four bread wheat [Triticum aestivum L.] genotypes, ‘Rushan,’ ‘Kavir,’ ‘Cross,’ and ‘Falat,’ and a durum wheat [Triticum durum L.] genotype, ‘Dur-3,’ at two zinc (Zn) rates (0 and 15 mg Zn kg−1 dry soil) and four salinity levels (0, 60, 120, and 180 mM NaCl) was conducted. After 45 d of growth, the shoots were harvested, and Zn, iron (Fe), potassium (K), sodium (Na), and cadmium (Cd) concentrations were determined. In the absence of added Zn, visual Zn deficiency symptoms were observed to be more severe in ‘Dur-3’ and ‘Kavir’ than in other genotypes. The effect of Zn deficiency on shoot dry matter was similar to its effect on visual deficiency symptoms, such that shoot growth was most depressed in ‘Kavir’ and ‘Dur-3.’ At the 180 mM treatment, Zn fertilization had no effect on shoot dry matter of genotypes. Genotypes with high Zn efficiency had greater shoot Zn content than genotypes with low Zn efficiency. In the absence of added Zn, the Dur-3, and ‘Cross’ genotypes had the highest and lowest Cd concentrations, respectively. Application of Zn had a positive effect on salt tolerance of plants.

Effects of zinc deficiency on rice growth and genetic factors contributing to tolerance.

Zinc (Zn) deficiency is the most widespread micronutrient disorder in rice (Oryza sativa), but efforts to develop cultivars with improved tolerance have been hampered by insufficient understanding of genetic factors contributing to tolerance. The objective of this paper was to examine alternative evaluation methods and to identify the most informative traits that would provide realistic information for rice breeders and to map quantitative trait loci (QTLs) associated with tolerance. Screening experiments in low-Zn nutrient solution and in a Zn-deficient field did not produce similar tolerance rankings in a set of segregating lines, which suggested that rhizosphere effects were of greater importance for lowland rice than internal Zn efficiency. The most severe symptom in the field was high plant mortality. The occurrence of leaf bronzing, usually regarded as indicative of susceptibility, did not necessarily concur with high plant mortality, which implied that both were under independent genetic control. The QTL mapping experiment conducted in the field with a population derived from a cross of IR74 (intolerant) with Jalmagna (tolerant) largely confirmed this. Four QTLs associated with plant mortality were detected, and only one of those colocalized with one of the four QTLs detected for leaf bronzing. The two most influential QTLs for plant mortality were detected on chromosomes 2 and 12. They explained 16.6% and 24.2% of the variation, and alleles of the tolerant donor parent Jalmagna reduced mortality by 16.6% and 14.8%, respectively. QTLs for plant mortality acted in a purely additive manner, whereas digenic epistatic interactions were important for leaf bronzing.

Determination of Zn Efficiency in Rice (Oryza sativa L.) Genotypes with Use of Response to Bicarbonate

Determination of Zn Efficiency in Rice (Oryza sativa L.) Genotypes with Use of Response to Bicarbonate

Zinc Deficiency in Selected Cultivars of Wheat and Barley as Tested in Solution Culture

The relative zinc (Zn) efficiencies of 33 wheat and 3 barley cultivars were determined by growing them in chelate‐buffered culture solutions. Zn efficiency, determined by growth in a Zn‐deficient solution relative to that in a medium containing an adequate concentration of Zn, was found to vary between 10% and 63% among the cultivars tested. Out of the 36 cultivars tested, 12 proved to be Zn efficient, 10 were Zn inefficient, and the remaining 14 varieties were classed as intermediate. The most Zn‐efficient cultivars included Bakhtawar, Gatcher S61, Wilgoyne, and Madrigal, and the most Zn inefficient included Durati, Songlen, Excalibur, and Chakwal‐86. Zn‐efficient cultivars accumulated greater amounts of Zn in their shoots than inefficient cultivars, but the correlation between shoot Zn and shoot dry matter production was poor. All the cultivars accumulated higher concentrations of iron (Fe), copper (Cu), manganese (Mn), and phosphorus (P) at deficient levels of Zn, compared with adequate Zn concentrations. The Zn‐inefficient cultivars accumulated higher concentrations of these other elements compared to efficient cultivars.

Zinc Tolerance in Wheat Cultivars as Affected by Varying Levels of Phosphorus

The effect of zinc–phosphorus (Zn‐P) interaction on Zn efficiency of six wheat cultivars was studied. The higher dry matter yields were observed when Zn was applied at 5 µg g−1 soil than with no Zn application. Phosphorus applications also increased dry matter yield up to the application of 25 µg P g−1 soil. The dry matter yield was significantly lower at the P rate of 250 µg g−1 soil. At the Zn‐deficient level, the Zn‐efficient cultivars had higher Zn concentrations in the shoots. Zinc concentrations in all cultivars increased when the P level in the soil was increased from 0 to 25 µg P g−1 soil except for the cv. Durati, in which Zn concentrations decreased with increases in P levels. However, when Zn×P interactions were investigated, it was observed that at a Zn‐deficient level, Zn concentrations in the plant shoot decreased with each higher level of P, and more severe Zn deficiency was observed at P level of 250 µg g−1 soil.

Contribution of Different Mechanisms to Zinc Efficiency in Bread Wheat During Early Vegetative Stage

Zinc (Zn) has a vast number of functions in plant metabolism and consequently Zn deficiency has a range of effects on plant growth. There are a number of different possible mechanisms by which plants tolerate Zn deficiency (generally expressed as Zn efficiency), such as Zn uptake, translocation to the shoot and physiological efficiency. However, there have been no direct comparisons of the relative importance of these possible mechanisms of Zn efficiency in a large set of genotypes of contrasting Zn efficiency. Soil and solution culture studies were conducted to examine the relative contribution of different mechanisms of Zn efficiency at the whole plant level in bread and durum wheat during early vegetative stage. Zn treatments were 0, 0.05, 0.1 and 1 mg/kg soil in the soil culture, and nil in the solution culture. Visual symptoms of Zn deficiency, dry matter production, Zn uptake, Zn distribution between roots and shoots, Zn utilization in roots and shoots and Zn remobilisation from the seed into growing parts were examined. Significant genotypic differences were observed in most criteria and responses differed with external Zn supply. The results of the present study suggest that while there are a number of different mechanisms contributing to Zn efficiency, uptake is the major mechanism and the effect of this is modified by the physiological efficiency within the shoot. Root:shoot partitioning was not strongly associated with Zn efficiency and seed Zn remobilisation was not linked to Zn efficiency. Visual symptoms of the severity of Zn deficiency was a good predictor of Zn efficiency and was correlated with Zn uptake.

Screening of sunflower cultivars for metal phytoextraction in a contaminated field prior to mutagenesis

Sunflower can be used for the remediation of metal-contaminated soils. Its high biomass production makes this plant species interesting for phytoextraction and using sunflower oil for a technical purpose may improve the economic balance of phytoremediation. The aim of the present field study was to screen 15 commercial cultivars of Helianthus annuus L., grown on metal-contaminated soil, to find out the variety with the highest metal extraction, which can be further improved by mutation or in vitro breeding procedures. Two different fertilizers (ammonium sulphate and ammonium nitrate) were also used to enhance the bioavailability of metals in soil. Highly significant differences were observed within tested varieties for metal accumulation and extraction efficiency. Furthermore, ammonium nitrate increased cadmium extraction, whereas ammonium sulphate enhanced zinc and lead uptake in most tested cultivars. In this field-based sunflower screening, we found enhanced cumulative Cd, Zn, and Pb extraction efficiency by a factor 4.4 for Salut cultivar. We therefore emphasize that prior to any classical breeding or genetic engineering enhancing metal uptake potential, a careful screening of various genotypes should be done to select the cultivar with the naturally highest metal uptake and to start the genetic improvement with the best available plant material.

Genetic Analysis on Agronomic Traits Related to Zinc Efficiency in Lowland Rice

The hereditary characteristics of plant traits related to zinc (Zn) efficiency in lowland rice (Oryza sativa L.) were analyzed in this study. The plant traits include the relative values of the total plant dry matter, shoot dry matter, root dry matter, leaf number, plant height, and root length of rice seedlings grown at low Zn2+ activity compared to those at sufficient Zn2+ activity. The F1 progeny was obtained by using a diallel cross between Zn-efficient and Zn-inefficient rice genotypes. The results revealed that the variances of dominant effect of all the traits studied were significant or very significant with the ratio being more than 65.4% of total variance. The additive effect variances of other traits except for the root length were also significant or very significant, with the average ratio being 21.85% of total variance. The variance of epistatic effect for root length was significant, with a ratio of 48% of total variance. The relative values of root length at low Zn2+ activity to sufficient Zn2+ activity was found to be governed by dominant and additive effects of hereditary genes. The relative values of leaf number, plant height and dry matter weight of rice seedlings were mainly governed by dominant effects of genes, secondarily by additive effects of genes. As the ability of rice tolerance to Zn deficiency was closely related to these agronomic traits, zinc efficiency in rice was mainly governed by dominant effects of genes, secondarily by additive effects of genes, and might be influenced by its epistatic effects of genes.

Micronutrient Constraints to Crop Production in Soils with Mediterranean-type Characteristics: A Review

Mediterranean-type soils generally have free CaCO3, high pH, and low organic matter. Consequently, nutrient disorders in these soils are the most important limiting factor to crop production, second only to moisture stress. Major problems are deficiencies of nitrogen and phosphorus; however, recent research has revealed that micronutrient problems are also hampering crop production. Unlike major nutrient deficiencies, micronutrient problems are highly genotype-specific and location-specific. Zinc (Zn) deficiency is the most widespread problem, because of factors like alkaline soil pH, calcareousness, low organic matter, exposed subsoils, Zn-free fertilizers, and/or flooding-induced electro-chemical changes. Now zinc sulfate is commonly used in rice, wheat, barley, potato, citrus, deciduous fruits, and many other crops. Soil-applied Zn has a relatively long residual effect. Efforts are also underway to develop crop varieties for higher Zn efficiency. Iron (Fe) chlorosis, the second most important micronutrient disorder, is induced by high soil in calcareous soils; high moisture and cold temperature accentuate it. Legumes, citrus, and deciduous fruits are more susceptible. Soil fertilization for iron is problematic; therefore, foliar feeding or breeding for tolerance remains the practical solutions. Boron (B) is a nonmetal micronutrient. While B deficiency has not been observed widely, research in the recent past has revealed this to be a widespread problem in crops like cotton, rapeseed, wheat, peanut, sorghum, and rice. The deficiency can be corrected by its soil application or by foliar feeding. As the concentration range between B deficiency and toxicity is exceptionally narrow, both are field-scale problems in the Mediterranean-type soils. Unlike B deficiency, B toxicity diagnosis is not simple, because of its accumulation in sub soils and resemblance of the symptoms with leaf fungal diseases. Also, B toxicity cannot be ameliorated for all practical purposes. Thus, breeding for B tolerance remains the only option. Luckily, many landraces of barley and wheat are quite tolerant to B toxicity. Deficiencies of manganese (Mn) and copper (Cu) are not a perceived problem, and availability of molybdenum (Mo) and chloride (Cl) is high in Mediterranean-type soils. Soil micronutrient deficiencies not only reduce crop productivity, but low Zn and Fe plant food is also adversely affecting human health and well-being. Though fertilizer use for micronutrients is highly cost-effective, actual use remains rather limited to a few specific crops in various countries. Thus, micronutrient problems are likely to be accentuated because of increased pressure on soil resources.

Differential expression of zinc efficiency during the growing season of barley

Considerable genetic variation exists in zinc (Zn) efficiency among cereal species and genotypes within the same species. Currently, the mechanisms of Zn efficiency are not understood well; however, the research so far suggests that overall Zn efficiency can be partitioned into uptake, utilisation and translocation or remobilisation efficiency, all or some of which collectively determine the level of Zn efficiency in a particular genotype. In a growth room study, using two barley genotypes differing in Zn efficiency (Zn-efficient Unicorn and Zn-inefficient Amagi Nijo), we attempted to determine which of these components of Zn efficiency contributed to greater Zn efficiency in Unicorn, by examining growth responses to Zn over a wide range of Zn fertilisation rates (0, 0.05, 0.2, 0.8, 3.2 and 12.8 mg Zn/kg soil) during the entire growth period. Zn-efficient Unicorn showed less severe Zn deficiency symptoms, produced more dry matter, and grain yield under Zn deficient conditions compared with Zn-inefficient Amagi Nijo. These responses also varied with the level of Zn deficiency stress and growth stage. Most importantly, the greater Zn efficiency (e.g., ability to grow well under Zn deficiency) at maturity of Unicorn was due to greater translocation of Zn from vegetative to reproductive organs or greater ability to produce higher grain yield with limited Zn rather than Zn uptake from soil which was similar in both genotypes. Zn-efficient Unicorn also had a lower critical deficiency concentration for grain (12 mg Zn/kg DW) than the Zn-inefficient Amagi Nijo (18 mg Zn/kg DW), suggesting a lower requirement for metabolic processes in Zn-efficient Unicorn. The critical deficiency concentration in the grain has the potential to diagnose Zn-deficient soils. The results also show that grain Zn concentration can be increased by Zn fertilisation, with significant increases occurring above the Zn fertilisation rate that is adequate for production of grain. However, genetic variation in grain Zn concentration should be explored and wild relatives of barley may offer potential for crop improvement for this trait.

Genotypic variation in common bean in response to zinc deficiency in calcareous soil

Greenhouse experiments have been carried out to study the genotypic variation among 35 bean (Phaseolus vulgaris L.) genotypes with regards to tolerance to zinc (Zn) deficiency (Zn efficiency). Plants were grown for 45 days in Zn deficient soil supplemented with 0 or 5 μg Zn g−1 soil) and analyzed for Zn efficiency, plant Zn concentration and content, and the distribution of Zn between old and young parts of the shoot. Zn efficiency (ZE) was defined as the ratio of dry matter production at low and high Zn supply and was calculated for the whole shoot as well as for young and old parts of the shoot. There were marked differences in ZE among the bean genotypes. Genotypes G4449 and G11360 were about 2-fold and 10-fold more Zn-efficient than G11229 and G3871 in whole shoot and young-part based ZE, respectively. Interestingly, the older portions of the shoot for most genotypes had higher dry matter production under Zn deficiency than under sufficient Zn supply, suggesting that there was a significant inhibition of new shoot growth and transport of photosynthates from source to sink organs under low-Zn conditions. Zinc concentrations of both old and young portions of the shoot did not correlate with ZE, but shoot Zn content was found to be significantly correlated with ZE. Furthermore, Zn-efficient genotypes distributed more Zn into young parts of the shoot under Zn-deficient conditions than did the inefficient lines. Variation in seed Zn content did not significantly influence the determination of ZE. We concluded that there is a substantial variation in Zn efficiency in the bean genome, and ZE based on analysis of the young shoot tissues represents a suitable screening technique for the evaluation of ZE in low-Zn soils.

The role of shoot-localized processes in the mechanism of Zn efficiency in common bean.

Zn efficiency (ZE) is the ability of plants to maintain high yield under Zn-deficiency stress in the soil. Two bean ( Phaseolus vulgaris L.) genotypes that differed in ZE, Voyager (Zn-efficient) and Avanti (Zn-inefficient), were used for this investigation. Plants were grown under controlled-environment conditions in chelate-buffered nutrient solution where Zn(2+) activities were controlled at low (0.1 pM) or sufficient (150 pM) levels. To investigate the relative contribution of the root versus the shoot to ZE, observations of Zn-deficiency symptoms in reciprocal grafts of the two genotypes were made. After growth under low-Zn conditions, plants of nongrafted Avanti, self-grafted Avanti and reciprocal grafts that had the Avanti shoot scion exhibited Zn-deficiency symptoms. However nongrafted and self-grafted Voyager, as well as reciprocal grafts with the Voyager shoot scion, were healthy with no visible Zn-deficiency symptoms under the same growth conditions. More detailed investigations into putative shoot-localized ZE mechanisms involved determinations of leaf biomass production and Zn accumulation, measurements of subcellular Zn compartmentation, activities of two Zn-requiring enzymes, carbonic anhydrase and Cu/Zn-dependent superoxide dismutase (Co/ZnSOD), as well as the non-Zn-requiring enzyme nitrate reductase. There were no differences in shoot tissue Zn concentrations between the Zn-inefficient and Zn-efficient genotypes grown under the low-Zn conditions where differences in ZE were exhibited. Shoot Zn compartmentation was investigated using radiotracer ((65)Zn) efflux analysis and suggested that the Zn-efficient genotype maintains higher cytoplasmic Zn concentrations and less Zn in the leaf-cell vacuole, compared to leaves from the Zn-inefficient genotype under Zn deficiency. Analysis of Zn-requiring enzymes in bean leaves revealed that the Zn-efficient genotype maintains significantly higher levels of carbonic anhydrase and Cu/ZnSOD activity under Zn deficiency. While these data are not sufficient to allow us to determine the specific mechanisms underlying ZE, they certainly point to the shoot as a key site where ZE mechanisms are functioning, and could involve processes associated with Zn compartmentation and biochemical Zn utilization.

Inheritance of tolerance to zinc deficiency in barley

AbstractBarley (Hordeum vulgare L.) is often grown on alkaline zinc (Zn)‐deficient soils where reductions in yield and grain quality are frequently reported. Currently, the use of Zn‐based fertilizer along with Zn‐deficiency‐tolerant genotypes is considered the most thorough approach for cropping the Zn‐deficient soils; however, developing or breeding genotypes with higher Zn efficiency requires a good understanding of the inheritance of tolerance to Zn deficiency. This study was conducted to determine genetic control of this trait in barley. Two parental cultivars ('Skiff, moderately tolerant; and ‘Forrest’, sensitive), 185 F2 plants, and 48 F2‐derived F3 families from this cross were screened to determine inheritance of tolerance to Zn deficiency using a visual score of deficiency symptoms. The segregation ratios observed indicated that greater tolerance to Zn deficiency in ‘Skiff compared with ‘Forrest’ at the seedling stage is controlled by a single gene with no dominance. The results also indicate that visual scores are useful for genetic analysis of tolerance to Zn deficiency.

Root–Shoot Ratio as Indicator of Zinc Uptake Efficiency of Different Potato Cultivars

Three potato cultivars, Kufri Badshah, Kufri Jyoti, and Kufri Chandramukhi were grown in low zinc (Zn) soil in the absence and presence of Zn in a pot experiment to test their Zn uptake efficiency. Two harvests were taken to obtain final dry matter accumulation (DMA), rates of shoot and root growth and Zn uptake rate per unit root length per unit time (Zn-influx). Taking the yield of the unfertilized relative to the fertilized plant as a measure of Zn efficiency, i.e., capacity of grow under low soil Zn supply, cv. Kufri Chandramukhi was less Zn efficient producing 71% total dry matter (shoot+tubers) as compared to cv. Kufri Jyoti and Kufri Badshah that produced 81 and 102%, respectively. Low Zn uptake efficiency of Kufri Chandramukhi was due to its low root length-shoot weight (DMA) ratio (4.7 m g−1) than Kufri Badshah (13.4 m g−1) and Kufri Jyoti (7.7 m g−1). Zinc influx did not differ significantly among cultivars in the absence of Zn. Lower Zn and higher K uptake efficiency of Kufri Chandramukhi than other cultivars have been discussed.

Zinc efficiency is correlated with enhanced expression and activity of zinc-requiring enzymes in wheat.

Zinc (Zn) is an essential micronutrient for plants. The ability of plants to maintain significant yields under low Zn is termed Zn efficiency (ZE) and its genetic and mechanistic basis is still not well understood. Previously, we showed that root Zn uptake did not play a role in ZE. In the current study, Zn-efficient and -inefficient wheat (Triticum aestivum) genotypes were grown for 13 d in chelate buffer nutrient solutions at low (0.1 pM), sufficient (150 pM), and high (1 microM) Zn(2+) activities and analyzed for root-to-shoot translocation of Zn, subcellular leaf Zn distribution, and activity and expression of the Zn-requiring enzymes in leaves. No correlation between ZE and Zn translocation to the shoot was found. Furthermore, total and water-soluble concentrations of leaf Zn were not associated with ZE, and no differences in subcellular Zn compartmentation were found between Zn-efficient and -inefficient genotypes. However, the expression and activity of the Zn-requiring enzymes copper (Cu)/Zn superoxide dismutase (SOD) and carbonic anhydrase did correlate with differences in ZE. Northern analysis suggested that Cu/ZnSOD gene expression was up-regulated in the Zn-efficient genotype, Kirgiz, but not in inefficient BDME. Under Zn deficiency stress, the very Zn-efficient genotype Kirgiz and moderately Zn-efficient Dagdas exhibited an increased activity of Cu/ZnSOD and carbonic anhydrase when compared with Zn-inefficient BDME. These results suggest that Zn-efficient genotypes may be able to maintain the functioning of Zn-requiring enzymes under low Zn conditions; thus, biochemical Zn utilization may be an important component of ZE in wheat.

Varietal tolerance to Zinc deficiency in wheat and barley grown in chelatorbuffered nutrient solution and its effect on uptake of Cu, Fe, and Mn

AbstractTolerance to zinc (Zn) deficiency was examined for three wheat (Triticum aestivum L.) and three barley (Hordeum vulgare L.) varieties grown in chelator‐buffered nutrient solution. Four indices were chosen to characterize tolerance to Zn deficiency: (1) relative shoot weight at low compared to high Zn supply (“Zn efficiency index”), (2) relative shoot to root ratio at low compared to high Zn supply, (3) total shoot uptake of Zn under deficient conditions, and (4) shoot dry weight under deficient conditions. Barley and wheat exhibited different tolerance to Zn deficiency, with barley being consistently more tolerant than wheat as assessed by all four indices. The tolerance to Zn deficiency in the barley varieties was in the order Thule=Tyra>Kinnan, and that of wheat in the order Bastian=Avle>Vinjett. The less tolerant varieties of both species accumulated more P in the shoots than the more tolerant varieties. For all varieties, the concentrations of Mn, Fe, Cu, and P in shoot tissue were negatively correlated with Zn supply. This antagonism was more pronounced for Mn and P than for Cu and Fe. Accumulation of Cu in barley roots was extremely high under Zn‐deficient conditions, an effect not so clearly indicated in wheat.

Effects of bicarbonate and high pH on growth of Zn-efficient and Zn-inefficient genotypes of rice, wheat and rye

A range of Zn efficient and inefficient genotypes of rice (Oryza sativa L.), wheat (Triticum aestivum L. and Triticum durum L.) and rye (Secale cereale L.) were investigated to examine shoot and root growth response to bicarbonate and high pH at different Zn levels. The treatment of bicarbonate was 10 mM as NaHCO3, high pH was 8.0 buffered with HEPES, and three Zn levels included without addition of Zn (deficient Zn), with 0.5 and 1.0 μM Zn (moderate Zn), and 1.5 and 3.5 μM (high Zn) for rice and wheat or rye, respectively. For rice, shoot and root growth of Zn-inefficient genotypes was strongly inhibited, whereas root length of Zn-efficient genotypes was considerably enhanced by bicarbonate. High pH had much less effect on reduced root growth of the Zn-inefficient rice genotypes and enhanced root length of the Zn-efficient genotypes, as compared with bicarbonate. Responses of plants to bicarbonate at different Zn levels showed that under deficient or moderate Zn supply conditions, root dry weight and length were significantly increased for the Zn-efficient rice genotypes, but were decreased for the Zn-inefficient rice genotypes grown with bicarbonate. At high Zn supply, however, root elongation of the Zn-efficient rice genotypes and of the Zn-inefficient genotypes was enhanced. In contrast to rice, either bicarbonate or high pH had little effects on shoot and root growth for all the Zn-efficient and Zn-inefficient wheat genotypes except for Dagdas (Zn-efficient) at moderate Zn levels. Decreased root growth due to bicarbonate treatment was observed only in the Zn-efficient rye. Root lengths of all the wheat and rye genotypes except for Kunduru (Zn-inefficient) were reduced by high pH but not affected by bicarbonate. At deficient Zn levels, shoot growth was reduced by bicarbonate for both Zn-efficient rye and inefficient wheat genotypes. Root lengths was reduced due to bicarbonate for the Zn-inefficient wheat genotype at deficient and high Zn, but not at moderate Zn levels. The results imply that Zn efficiency in rice is closely associated with plant tolerance to bicarbonate relative to root growth, and bicarbonate tolerance and Zn efficiency might be developed simultaneously in lowland rice.

Zn fertilization improves water use efficiency, grain yield and seed Zn content in chickpea

In a number of the major chickpea-growing areas in the world, rainfed crops of chickpeas are often grown on soils with low available zinc (Zn). Consequently, chickpea crops can be challenged by soil water deficits and Zn deficiency coincidentally during the growing season. The interaction between these stresses was examined in two glasshouse experiments using genotypes differing in Zn efficiency. Water stress was imposed during podding. Increasing the level of Zn resulted in large and significant increases in vegetative growth up to podding. Applying Zn increased grain yields when the plants were well watered, but not under water stress, except for the Zn-efficient and drought-resistant genotype ICC-4958. Harvest indices were generally reduced as the supply of Zn and water increased. Applying Zn increased water use and water use efficiency of chickpea. Yields were reduced by water stress, largely due to fewer pods set per plant. Losses from water stress were greatest at the highest level of Zn, which was attributed to the limited soil volume afforded by the pots and the rapid development of stress in the larger plants grown at adequate levels of Zn. However, at each level of Zn, the loss in yield from water stress tended to be less in a Zn-efficient genotype. The major factor determining the distribution of Zn in the plant was the supply of Zn, while differences due to water stress and genotype were relatively small. Two-thirds of the Zn present in the plant at maturity was accumulated after the start of podding and this was little affected by water stress. The proportion of Zn in the roots of Zn-deficient plants was less than that in Zn-adequate plants. As the Zn supply increased, Zn accumulation was higher in leaves than in the stem and reproductive parts, due to combined effect of both higher Zn concentration and higher dry matter. At maturity, senesced leaves and pod walls had relatively lower concentrations of Zn compared to leaves and pods at the start of podding in all Zn treatments. In contrast, the Zn content in the stem either increased or remained unchanged. At maturity, Zn accumulation in plant organs generally increased with increasing Zn supply, but the largest proportion of Zn was found in the seeds, which is a beneficial nutritional trait for human nutrition.