Effect of zinc fertilization on the mineral nutrition of rices differing in tolerance to zinc deficiency

Summary The effects of four Zn levels on the electrochemical and chemical properties of the soil solution, and on the growth and mineral nutrition of two rice varieties (IR26 and IR34) differing in tolerance to Zn deficiency were studied in the greenhouse using Zn-deficient soils from two locations. A similar experiment was conducted in culture solution to check how Zn addition affects translocation of other nutrients.In both soil and culture solution, plant Zn concentrations alone was not enough to account for varietal tolerance to Zn deficiency. Comparison of nutrient to Zn and shoot to root ratios of nutrients was more useful in determining the possible mechanism of varietal tolerance. IR 34 appeared to tolerate the disorder due to its lower Zn requirement, more efficient Zn translocation and ability to maintain lower Fe/Zn, Cu/Zn, Mg/Zn and P/Zn ratios in the shoot than the more susceptible variety, IR26. This was shown to be due to decreased translocation of Fe, Mg and P to shoots and decreased absorption of Cu by the root in IR34 in culture solution studies. Adding Zn further reduces translocation or absorption of these nutrients and depending on the nutrient supply of the soil, could cause deficiencies or mineral imbalances, especially of Fe, Cu, and P.These observed varietal differences regarding Zn requirement and the interaction of Zn with absorption and translocation of plant nutrients necessitates revision of recommendations for Zn fertilization. There is an inevitable need for Zn application in severely Zn-deficient soils regardless of rice variety. But on marginally Zn-deficient soils especially those low in Fe, Cu, or P, Zn fertilization is not advisable when resistant rice varieties are used.     

Genetic analysis of the effect of zinc deficiency on Arabidopsis growth and mineral concentrations

Aims

Zinc deficiency is a common micronutrient deficiency in plants growing in many different regions of the world and is associated with disturbances in uptake and accumulation of mineral nutrients. Despite many published data on physiological factors affecting ion accumulation in Zn deficient plants, there is very little information about the genetic factors underlying this. We aim to identify genetic loci involved in mineral accumulation and plant performance under Zn deficiency.

Methods

Genetic loci were identified using the genetically segregating Ler × Cvi recombinant inbred line (RIL) population grown under Zn deficient conditions. Lines were analysed for the concentrations of Zn, Fe, Mn, K, Ca, Mg, P, Cu, S and Al in shoot dry matter. The same was done for the same lines grown under Zn sufficient conditions.

Results

We found considerable heritable variation for most mineral concentrations. In general, there was a positive correlation between mineral concentrations. For Zn only condition-dependent QTLs were identified, while for most other mineral concentrations both condition-dependent and -independent QTLs were identified. Several QTLs co-localize, including co-localization to loci controlling shoot biomass and to mineral concentration loci found previously in this and other RIL populations.

Conclusions

There are different genetic loci controlling Zn accumulation under deficient and sufficient Zn supply. Only for few minerals, their accumulation is controlled by Zn-supply-specific loci.     

Calcicole behaviour of Callisthene fasciculata Mart., an Al‐accumulating species from the Brazilian Cerrado

• Most aluminium (Al)‐accumulating species are found on soils with high Al saturation and low Ca availability (Ca poor). Callisthene fasciculata Mart. (Vochysiaceae), however, is an Al‐accumulating tree restricted to Ca‐rich soils with low Al saturation in the Brazilian Cerrado savanna. Here we tested its calcicole behaviour, and the possible role of organic acids in detoxification of Al during the early stages of plant development.
• We assessed growth, dry mass, nutrients, Al and organic acids in seedlings grown for 50 days on two contrasting Cerrado soils; one with high Ca concentrations and low Al saturation and the other with low Ca availability and high Al saturation.
• Relative to plants on Ca‐rich soil, plants on Ca‐poor soil had necrotic spots and bronzing of leaves. Roots and shoots contained reduced concentrations of P and Cu, but higher concentrations of Fe, Al and citrate. Despite lower concentrations in the soil, Ca and Mg increased in shoots. Shoot concentrations of oxalate were also higher.
• We confirmed C. fasciculata as an Al‐accumulating species with calcicole behaviour. The increased concentrations of organic acids in plants with higher Al accumulation suggest that high availability of soluble Al does not prevent occurrence of this species on soils with high Al saturation. Instead, the absence of C. fasciculata from Ca‐poor soils is probably due to imbalances in tissue Fe, Cu and Zn imposed by this soil type.

     

Iron-dependent changes of heavy metals,nicotianamine, and citrate in different plant organs and in the xylem exudate of two tomato genotypes. Nicotianamine as possible copper translocator

The influence of Fe nutrition on the distribution of the heavy metals Fe, Mn, Zn, and Cu and of the heavy metal chelators nicotianamine (NA) and citrate in 6 different shoot and 3 different root parts and in xylem exudate of a NA-containing tomato wild type and its NA-less mutant was investigated. Under the same Fe supply the mutant showed higher Fe, Mn, and Zn concentrations in all organs investigated, with exception of the shoot apex. The Cu concentration in the mutant was only in root parts higher than in the wild type but much lower in leaves. Analyses of xylem exudate showed that Fe, Mn, and Zn were readily translocated by both genotypes from the roots to the shoot at all levels of Fe supply, whereas in the absence of NA, Cu was only poorly transported. Citrate as main Fe chelator in the xylem was present in high concentrations in xylem exudate of the wild type under low Fe supply but in the mutant also at 10 M FeEDTA. NA occurred in xylem exudate of the wild type in concentrations high enough to chelate heavy metal ions.Generally, high Fe supply induced a decrease of Mn, Cu, and Zn concentrations in all organs of the wild type whereas high concentrations were observed in most cases under Fe deficiency. A positive correlation between Fe supply and NA concentration existed only in the shoot apex and in the xylem exudate of wild type plants. From the correlation between Cu and NA translocation and from the high stability constant of the NA-Cu-complex (log K=18.6) it is concluded that NA is a chelator for Cu in the xylem, whereas the translocation of Fe, Mn, and Zn is independent of NA.     

Zinc deficiency as a critical problem in wheat production in Central Anatolia

In a soil and plant survey, and in field and greenhouse experiments the nutritional status of wheat plants was evaluated for Zn, Fe, Mn and Cu in Central Anatolia, a semi-arid region and the major wheat growing area of Turkey.All 76 soils sampled in Central Anatolia were highly alkaline with an average pH of 7. 9. More than 90% of soils contained less than 0.5 mg kg^-1 DTPA-extractable Zn, which is widely considered to be the critical deficiency concentration of Zn for plants grown on calcareous soils. About 25% of soils contained less than 2.5 mg kg^-1 DTPA-extractable Fe which is considered to be the critical deficiency concentration of Fe for plants. The concentrations of DTPA-extractable Mn and Cu were in the sufficiency range. Also the Zn concentrations in leaves were very low. More than 80% of the 136 leaf samples contained less than 10 mg Zn kg^–1. By contrast, concentrations of Fe, Mn and Cu in leaves were in the sufficient range.In the field experiments at six locations, application of 23 kg Zn ha^-1 increased grain yield in all locations. Relative increases in grain yield resulting from Zn application ranged between 5% to 554% with a mean of 43%. Significant increases in grain yield (more than 31%) as a result of Zn application were found for the locations where soils contained less than 0.15 mg kg^-1 DTPA-extractable Zn.In pot experirnents with two bread (Triticum aestivum, cvs. Gerek-79 and Kirac-66) and two durum wheats (Triticum durum, cvs. Kiziltan-91 and Kunduru-1149), an application of 10 mg Zn kg^-1 soil enhanced shoot dry matter production by about 3.5-fold in soils containing 0.11 mg kg^-1 and 0.15 mg kg^-1 DTPA-extractable Zn. Results from both field observations and greenhouse experiments showed that durum wheats were more susceptible to Zn deficiency than the bread wheats. On Zn deficient soils, durum wheats as compared to bread wheats developed deficiency symptoms in shoots earlier and to a greater extent, and had lower Zn concentration in shoot tissue and lower Zn content per shoot than the bread wheats.The results presented in this paper demonstrate that (i) Zn deficiency is a critical nutritional problem in Central Anatolia substantially limiting wheat production, (ii) durum wheats possess higher sensitivity to Zn deficient conditions than bread wheats, and (iii) wheat plants grown in calcareous soils containing less than 0.2 mg kg^-1 DTPA-extractable Zn significantly respond to soil Zn applications. The results also indicate that low levels of Zn in soils and plant materials (i.e. grains) could be a major contributing factor for widespread occurrence of Zn deficiency in children in Turkey, whose diets are dominated by cereal-based foods.     

Effect of submergence on availability of certain plant nutrients in three Ultisol catenas

Soil samples from surface and sub-surface horizons in the well-drained and poorly-drained members of three soil catenas were incubated under submergence or at field capacity to study the effects of these incubation conditions and prior natural drainage on the solubility of four plant micro-nutrients. Iron, Mn, Zn and Cu were extracted by water using a 11 water:soil ratio. The four micronutrient metals were also extracted by DTPA solutions buffered at either pH 5.3 or pH 7.3 to compare the effectiveness of these two extractants under these incubation conditions with acid soils. Generally the extractability of the nutrients was much affected by the horizon (A, E or B) with A horizons having the greatest amounts of all nutrients and undergoing greater changes in water- and DTPA-extractability during incubation. Soil drainage class (wellvs. poorly drained) had few effects. Incubation moisture regime had major effects on water extractable Fe and Mn with lesser effects on Zn and Cu. Submerged soils generally had the greatest levels of water extractable nutrients, though rice uptake did not reflect this. DTPA at pH 5.3 extracted 2 to 3 times as much Fe, Mn, Zn and Cu as did DTPA at pH 7.3 and about 50 to 100 times as much as did water. Correlations between DTPA extractable nutrients and rice uptake were significant only for Fe and Cu and declined during incubation. The changes in all variables during incubation were complex, being related to soil properties such as organic matter content, pH and mineralogy as well as to incubation conditions.     

Influence of organic matter on the availability of certain elements to barley seedlings grown by a modified neubauer method

Summary The influence of organic matter on the availability of 17 elements (Na, K, Cs¹³⁷, Mg, Ca, Sr, Ba, N, P, B, Cu, Zn, Fe, Mn, Mo, Al, and Si) to barley seedlings grown by a modified Neubauer technique was determined. Three different soils that were treated with dry ground mustard spinach leaves (1 g/100 g soil) and incubated for various lengths of time (0, 1, 2, 5, 9, 13, and 17 weeks) in moist condition before cropping were used for this study.The addition of organic matter to the soils increased the plant yields. The average N and K concentrations were consistently increased in the plants grown in soils with added organic matter. The average concentration of B, P, Na, Mg, Sr, Ba, and Si were almost consistently decreased in the plants. The average contents of Cu, Zn, Fe, Mn, Mo, Ca, and Al varied with the soil types and precropping incubation time. The average Cs¹³⁷ contents of the plants were reduced considerably by the addition of organic matter to the soils. The reduction of Cs¹³⁷ contents ranged from 29 to 75 per cent, depending on the pre-cropping incubation time and soil type. The main factors causing this reduction were considered to be microbial immobilization, ion antagonism by K, carbohydrate dilution, and the state of decomposition and the kind of organic matter added to the soils.     

Micronutrient availability to cereals from calcareous soils

Summary On several alkaline calcareous soils, Zn and Cu deficiency occurred mainly in lowland rice (Oryza sativa L.) and was rarely found in wheat (Triticum aestivum L.). Zinc and Cu requirement of plants was not responsible as the critical Zn and Cu contents in tops of the two plant species were almost similar i.e. 17.4, 6.5 and 14.5, 5.6 ppm respectively. Neither did rice absorb Zn and Cu less efficiently. On the contrary, their rates of absorption in rice were double than in wheat. They were 22.2, 6.3 and 10.2, 3.3 ng atoms/g fresh root/h respectively in the two plant species. Flooded soil conditions appeared to be responsible for Zn and Cu deficiency in rice as their deficiency was found mainly in plant samples collected from continuously flooded fields. The mechanism is not known.Both Zn and Cu inhibited uptake of each other in wheat on most of the soils. In rice, only applied Zn depressed Cu uptake but Cu had generally little effect on Zn uptake. Little Cu inhibition of Zn uptake in lowland rice seems to be related to flooded soil conditions. The mechanism is yet to be known. The antagonising element accentuated the deficiency of the other element both in wheat and rice and severely reduced their yields on soils marginal to deficient in Zn or Cu supplies. It is recommended that their soil availability status should be thoroughly considered before their fertilizers are applied. re]19750515     

Metal mobilization from soils by phytosiderophores – experiment and equilibrium modeling

Aims

To test if multi–surface models can provide a soil-specific prediction of metal mobilization by phytosiderophores (PS) based on the characteristics of individual soils.

Methods

Mechanistic multi-surface chemical equilibrium modeling was applied for obtaining soil-specific predictions of metal and PS speciation upon interaction of the PS 2’-deoxymugineic acid (DMA) with 6 soils differing in availability of Fe and other metals. Results from multi-surface modeling were compared with empirical data from soil interaction experiments.

Results

For soils in which equilibrium was reached during the interaction experiment, multi-surface models could well predict PS equilibrium speciation. However, in uncontaminated calcareous soils, equilibrium was not reached within a week, and experimental and modeled DMA speciation differed considerably. In soils with circum-neutral pH, on which Fe deficiency is likely to occur, no substantial Fe mobilization by DMA was predicted. However, in all but the contaminated soils, Fe mobilization by DMA was observed experimentally. Cu and Ni were the quantitatively most important metals competing with Fe for complexation and mobilization by DMA.

Conclusion

Thermodynamics are unable to explain the role of PS as Fe carrier in calcareous soils, and the kinetic aspects of metal mobilization by PS need to be closer examined in order to understand the mechanisms underlying strategy II Fe acquisition.     

Tolerance and bioaccumulation of copper in Phragmites australis and Zea mays

The effects of copper on the growth, tolerance indices, mineral composition (N, P, K, Fe, Zn and Mn) and metal uptake of reed (Phragmites australis [Cav. Trin. ex Steudel]) and maize (Zea mays L.) were investigated in hydroponic experiments at copper concentrations ranging from 0.5 to 157 M Cu. A reduction in root length was shown to be a good indicator of copper toxicity, concentrations of 15.7 and 78.7 M Cu inhibiting root growth in maize and reed, respectively. The reed was significantly more tolerant of copper than maize and at 7.85 M Cu (external concentration), reed can be described as a Cu tolerant plant, and maize as a Cu non-tolerant species. As a result of Cu toxicity, the concentrations of macronutrients N, P and K decreased in both shoot and root of maize, while the concentrations were hardly affected in reed tissues. Fe concentration increased in shoots and roots of maize and in roots of reed with increasing Cu treatments, leading to highly significant (p<0.01) linear relationships between tissue Fe and Cu concentrations. The bioconcentration factor (BCF) of Cu was higher in roots than in shoots of both plant species, ranging from 612 to 1592 in reed for the Cu treatments tested. In the roots of maize, BCF of Cu increased from 349 to 1931 when increasing Cu in nutrient solution from 7.85 M to 78.5 M. Therefore, reed could be useful in wastewater treatments for the removal of Cu. However, the use of reed in phytoextraction of Cu from contaminated soils is limited by the low accumulation rate in shoots and although reed can be more efficient than maize for Cu phytoextraction, harvesting the full biomass, including roots, may be required.     

Distribution of manganese and other biometals in <Emphasis Type="Italic">flatiron</Emphasis> mice

Flatiron (ffe) mice display features of “ferroportin disease” or Type IV hereditary hemochromatosis. While it is known that both Fe and Mn metabolism are impaired in flatiron mice, the effects of ferroportin (Fpn) deficiency on physiological distribution of these and other biometals is unknown. We hypothesized that Fe, Mn, Zn and/or Cu distribution would be altered in ffe/+ compared to wild-type (+/+) mice. ICP-MS analysis showed that Mn, Zn and Cu levels were significantly reduced in femurs from ffe/+ mice. Bone deposits reflect metal accumulation, therefore these data indicate that Mn, Zn and Cu metabolism are affected by Fpn deficiency. The observations that muscle Cu, lung Mn, and kidney Cu and Zn levels were reduced in ffe/+ mice support the idea that metal metabolism is impaired. While all four biometals appeared to accumulate in brains of flatiron mice, significant gender effects were observed for Mn and Zn levels in male ffe/+ mice. Metals were higher in olfactory bulbs of ffe/+ mice regardless of gender. To further study brain metal distribution, ⁵⁴MnCl₂ was administered by intravenous injection and total brain ⁵⁴Mn was measured over time. At 72 h, ⁵⁴Mn was significantly greater in brains of ffe/+ mice compared to +/+ mice while blood ⁵⁴Mn was cleared to the same levels by 24 h. Taken together, these results indicate that Fpn deficiency decreases Mn trafficking out of the brain, alters body Fe, Mn, Zn and Cu levels, and promotes metal accumulation in olfactory bulbs.     

Interaction of lead with some essential elements in rat’s kidney in relation to age

The aim of this study was to evaluate the interaction of lead given orally with Fe, Zn, and Cu in adult female rats and in their pups. Kidney was chosen for studying this interaction. Four different doses of lead (acetate) from 1500 to 7500 ppm were administered to mature female albino rats in beverages during 6 wk. The exposure lasted from mating up to 3 wk after delivery. Pb, Fe, Zn, and Cu were determined in kidneys of mothers and pups. Histopathological examinations were also performed. Results showed significantly lower concentrations of Fe, Zn, and Cu in kidneys of mothers on all lead levels. Their pups showed no change in concentrations of essential elements and even increased Fe at the highest exposure level. Concentrations of Pb and histopathological changes in the kidney were similar in mothers and offspring, although pups received only a fraction of the mothers’ doses. Our results indicate that in immature animals the interaction of Pb with essential elements in the kidney is different from that in their mothers.     

Effect of various metal ions on growth of two wheat lines known to differ in aluminium tolerance

The effects of aluminium (Al), manganese (Mn), zinc (Zn), copper (Cu), boron (B), iron (Fe), gallium (Ga), scandium (Sc) and lanthanum (La) on growth of an Al-tolerant and an Al-sensitive line of wheat (Triticum aestivum L.) were measured in solution culture. The concentrations of nutrients in the basal nutrient solution were (M) 500 Ca, 100 Mg, 300 K, 600 N (150 NH₄, 450 NO₃), 600 SO₄, 2.5 P, 3 B, 2.5 Fe, 0.5 Zn, 0.5 Mn, 0.1 Cu at a pH of 4.7. The major solution nutrient concentrations were maintained at the nominal concentration with monitoring, frequent additions and weekly renewal. Differentiation in yield between the Al-tolerant and Al-sensitive line only occurred in the presence of Al indicating that, in the long term, none of the other metals tested could be used as an analog for Al. The visual symptoms in the roots of Cu toxicity (in both lines) and Al toxicity (in the sensitive line) were similar. The solution concentration (M) at which yield of the roots of the tolerant line was reduced by 50% was, in order of increasing tolerance, Cu 0.5, Sc 1.1, La 7.1, Ga 8.6, Al 15, Zn 19, Fe 84, B 490 and Mn 600.     

Heavy Metals and Other Elements in Serum of Cattle from Organic and Conventional Farms

Concentrations of cadmium, lead, iron, zinc, copper, chromium, nickel, aluminium and arsenium were analysed in blood serum of cattle from organic (n = 20) and conventional (n = 21) farms. The elements were determined by inductively coupled plasma atomic emission spectrometry using an Optima 2000 DV instrument (Perkin Elmer Inc.). Animals from the organic farm were characterised by significantly lower (P < 0.01) serum concentrations of Pb, Zn, Fe, Cu, Cr, Ni, As and Al compared to animals from the conventional farm. The concentration of Cd was similar in animals from both organic and conventional farms. The concentration of toxic elements in cattle from organic and conventional farms studied was very low. The trace essential elements were generally within the adequate ranges except Zn and Cu, which were deficient. In organically reared animals, also serum Fe content was below the critical level for diagnosing iron deficiency. Pb was significantly correlated with Cd, Zn, Fe, Cu and Ni. A significant positive correlation between the concentration of Cd and Zn, Cu and Ni concentrations was only observed in cows from the organic farm. The present results suggest that organically raised animals are less exposed to harmful environmental influences such as the environmental pollution with heavy metals. On the other hand, these animals are at a greater risk of mineral deficiency compared to animals kept on conventional farms.     

Spatial X-ray fluorescence micro-imaging of minerals in grain tissues of wheat and related genotypes

Main conclusion

Wheat and its related genotypes show distinct distribution patterns for mineral nutrients in maternal and filial tissues in grains. X-ray-based imaging techniques are very informative to identify genotypes with contrasting tissue-specific localization of different elements. This can help in the selection of suitable genotypes for nutritional improvement of food grain crops.

Abstract

Understanding mineral localization in cereal grains is important for their nutritional improvement. Spatial distribution of mineral nutrients (Mg, P, S, K, Ca, Fe, Zn, Mn and Cu) was investigated between and within the maternal and filial tissues in grains of two wheat cultivars (Triticum aestivum Cv. WH291 and WL711), a landrace (T. aestivum L. IITR26) and a related wild species Aegilops kotschyi, using micro-proton-induced X-ray emission (µ-PIXE) and micro-X-ray fluorescence (µ-XRF). Aleurone and scutellum were major storage tissues for macro (P, K, Ca and Mg) as well as micro (Fe, Zn, Cu and Mn) nutrients. Distinct elemental distribution patterns were observed in each of the four genotypes. A. kotschyi, the wild relative of wheat and the landrace, T. aestivum L. IITR26, accumulated more Zn and Fe in scutellum and aleurone than the cultivated wheat varieties, WH291 and WL711. The landrace IITR26, accumulated far more S in grains, Mn in scutellum, aleurone and embryo region, Ca and Cu in aleurone and scutellum, and Mg, K and P in scutellum than the other genotypes. Unlike wheat, lower Mn and higher Fe, Cu and Zn concentrations were noticed in the pigment strand of A. kotschyi. Multivariate statistical analysis, performed on mineral distribution in major grain tissues (aleurone, scutellum, endosperm and embryo region) resolved the four genotypes into distinct clusters.     

Copper in plant species in a copper gradient in Catalonia (North East Spain) and their potential for phytoremediation

The accumulation of Cu in roots and shoots of 32 plant species growing on soils with a wide range of Cu concentrations (30–18 500 g g^–1 total soil Cu) located in Collserola Mountain (Barcelona, Spain) was analysed. High Cu availability decreased the species diversity in the Hyparrhenietum hirto-pubescentis, the natural plant association at the study sites. Shoot and root Cu concentrations in relation to extractable soil Cu concentrations were used for the evaluation of the Cu resistance strategy in the different species. Saturation of Cu accumulation in roots was observed in most species. Hyparrhenia hirta was the most efficient shoot excluder, while the linear increase of shoot Cu with the Cu soil concentration exhibited the highest slope in Hirschfeldia incana. Most species accumulated more Cu in roots than in shoots. High shoot/root Cu ratios were only found in the highly Cu-resistant Hirschfeldia incana, in the resistant or moderately resistant Spartium junceum and Reseda sp. (R. lutea and R. phyteuma), and in the much less resistant Ononis natrix. Only two species, Hirschfeldia incana and Sedum sediforme were able to support the extreme Cu-toxicity conditions on soils with 5000–16 800 g g^–1 extractable Cu. Among the grass species tested Hyparrhenia hirta was the most Cu-resistant species (up to 1950 g g^–1 extractable soil Cu). The potential usefulness of these pseudometallophytes for phytoremediation of Cu-contaminated soils is discussed.     

Iron deficiency in peach trees: effects on leaf chlorophyll and nutrient concentrations in flowers and leaves

The effects of iron deficiency on the leaf chlorophyll concentrations and on the macro- (N, P, K, Ca and Mg) and micro-nutrient (Fe, Mn, Zn and Cu) composition of flowers (at full bloom) and leaves (60 and 120 days after full bloom) of field-grown peach (Prunus persica L. Batsch) trees were investigated. Flowers and leaves were taken and analysed from fifty individual trees. Our data indicate that large decreases in leaf chlorophyll concentration were found at the beginning of the season in control trees, possibly associated to a dilution effect by leaf growth, that were later followed by leaf chlorophyll concentration increases. Leaf Fe chlorosis apparently results from two different processes, the dilution of leaf Chl caused by growth and the subsequent inability to produce and/or stabilize new Chl molecules in the thylakoid membrane. Iron chlorosis did not change the seasonal change patterns of any of the nutrients studied. In Fe-deficient trees the K concentration and the K/Ca ratio were high not only in leaves but also in flowers, indicating that this is a characteristic of Fe-deficient plant tissue in the whole fruit tree growing season. Flower Fe concentrations were well correlated with the degree of chlorosis developed later in the season by the trees, suggesting that flower analysis could be used for the prognosis of Fe deficiency in peach.     

Root exudation and microflora populations in rhizosphere of crop genotypes differing in tolerance to micronutrient deficiency

Crop genotypes differ in their tolerance to micronutrient-deficient soils, but the underlying mechanisms are poorly understood. This paper reviews information on mechanisms of tolerance to Zn and Mn deficiency, concentrating on plant-induced changes in chemistry and biology of rhizosphere that alter availability of Zn and Mn.When grown under conditions of Zn deficiency, wheat genotypes more tolerant of Zn deficiency released greater amounts of phytosiderophore, 2-deoxymugineic acid, than the sensitive genotypes. In addition, Zn deficiency increased numbers of fluorescent pseudomonads in rhizosphere of all wheat genotypes tested, but the effect was particularly obvious for genotypes tolerant of Zn deficiency.Rhizosphere of wheat genotypes contained an increased proportion of Mn reducers under Mn-deficiency compared to Mn-sufficiency conditions. When grown in soils of low Mn availability, some wheat genotypes tolerant of Mn deficiency (like cv. Aroona) had a greater ratio of Mn-reducers to Mn-oxidisers in the rhizosphere compared to the sensitive genotypes. In contrast, microflora in the rhizosphere of other wheat genotypes tolerant of Mn deficiency (like C8MM) did not show the same response as Aroona. It therefore appears that different mechanisms may underlie the expression of tolerance to Mn deficiency in wheat genotypes.It is concluded that wheat genotypes tolerant of Zn or Mn deficiency have a capacity to alter chemical and biological properties of the rhizosphere, thus increasing availability of critical micronutrients.     

Characterization of grain protein content gene (<Emphasis Type="Italic">GPC</Emphasis>-<Emphasis Type="Italic">B1</Emphasis>) introgression lines and its potential use in breeding for enhanced grain zinc and iron concentration in spring wheat

At least two billion people around the world suffer from micronutrient deficiency, or hidden hunger, which is characterized by iron-deficiency anemia, vitamin A and zinc deficiency. As a key staple food crop, wheat provides 20% of the world’s dietary energy and protein, therefore wheat is an ideal vehicle for biofortification. Developing biofortified wheat varieties with genetically enhanced levels of grain zinc (Zn) and iron (Fe) concentrations, and protein content provides a cost-effective and sustainable solution to the resource-poor wheat consumers. Large genetic variation for Fe and Zn were found in the primitive and wild relatives of wheat, the potential high Zn and Fe containing genetic resources were used as progenitors to breed high-yielding biofortified wheat varieties with 30–40% higher Zn content. Grain protein content (GPC) determines processing and end-use quality of wheat for making diverse food products. The GPC-B1 allele from Triticum turgidum L. var. dicoccoides have been well characterized for the increase in GPC and the associated pleiotropic effect on grain Zn and Fe concentrations in wheat. In this study effect of GPC-B1 allele on grain Zn and Fe concentrations in wheat were measured in different genetic backgrounds and two different agronomic management practices (with- and without foliar Zn fertilization). Six pairs of near-isogenic lines differing for GPC-B1 gene evaluated at CIMMYT, Mexico showed that GPC-B1 influenced marginal increase for grain Zn, Fe concentrations, grain protein content and slight reduction in kernel weight and grain yield. However, the magnitude of GPC and grain Zn and Fe reductions varied depending on the genetic background. Introgression of GPC-B1 functional allele in combination with normal or delayed maturity alleles in the CIMMYT elite wheat germplasm has the potential to improve GPC and grain Zn and Fe concentrations without the negative effect on grain yield due to early senescence and accelerated maturity.     

Plant Seeds as Mineral Nutrient Resource for Seedlings--A Comparison of Plants from Calcareous and Silicate Soils

Mineral nutrients of seeds constitute a significant source ofessential elements to seedlings and developing individuals ofvascular plants. In spite of their potential ecological significance,seed nutrient pools have attracted little attention with respectto calcifuge–calcicole behaviour of plants. The objectivesof this study were, therefore, to compare concentrations of13 macro- and micronutrients (K, Rb, Mg, Ca, Mn, Fe, Co, Cu,Zn, Mo, B, P and S) in seeds and leaves of 35 mainly herbaceousvascular plant species growing on both limestone (calcareous)and silicate (non-calcareous) soils. Concentrations of Rb andCo in seeds of plants originating from limestone soils were,on average, about half of those from silicate soils. Concentrationsof Mn, Mg, Zn and P of seeds were, or tended to be, lower orslightly lower in limestone-soil plants, whereas mean Ca andMo concentrations were higher. Comparing seed and leaf concentrationsof the same species from limestone and silicate soils generallydemonstrated a high P enrichment ratio, but a particularly lowK enrichment ratio in seeds, valid for both types of soil. Itwas also apparent that Fe and Mn, micronutrients which are lessreadily solubilized and taken up by plants on limestone soils,had significantly higher seed:leaf concentration ratios in plantsfrom limestone than from silicate soils, whereas the oppositewas true for Ca. This indicates a ‘strategy’ tosatisfy the demand of seedlings for elements which are lessreadily available in the soil.Copyright 1998 Annals of BotanyCompany Seed, leaf, plant, nutrient, content, calcareous, silicate, acid, soil.