Ayfer Alkan Torun

Triticum dicoccoides: an important genetic resource for increasing zinc and iron concentration in modern cultivated wheat

Abstract One major strategy to increase the level of zinc (Zn) and iron (Fe) in cereal crops, is to exploit the natural genetic variation in seed concentration of these micronutrients. Genotypic variation for Zn and Fe concentration in seeds among cultivated wheat cultivars is relatively narrow and limits the options to breed wheat genotypes with high concentration and bioavailability of Zn and Fe in seed. Alternatively, wild wheat might be an important genetic resource for enhancing micronutrient concentrations in seeds of cultivated wheat. Wild wheat is widespread in diverse environments in Tarkey and other parts of the Fertile Crescent (e.g., Iran, Iraq, Lebanon, Syria, Israel, and Jordan). A large number of accessions of wild wheat and of its wild relatives were collected from the Fertile Crescent and screened for Fe and Zn concentrations as well as other mineral nutrients. Among wild wheat, the collections of wild emmer wheat, Triticum turgidum ssp. dicoccoides (825 accessions) showed impressive variation and the highest concentrations of micronutrients, significantly exceeding those of cultivated wheat. The concentrations of Zn and Fe among the dicoccoides accessions varied from 14 to 190 mg kg−1 DW for Zn and from 15 to 109 mg kg−1 DW for Fe. Also for total amount of Zn and Fe per seed, dicoccoides accessions contained very high amount of Zn (up to 7 μg per seed) and Fe (up to 3.7 μg per seed). Such high genotypic variation could not be found for phosphorus, magnesium, and sulfur. In the case of modern cultivated wheat, seed concentrations of Zn and Fe were lower and less variable when compared to wild wheat accessions. There was a highly significant positive correlation between seed concentrations of Fe and Zn. Screening different series of dicoccoides substitution lines revealed that the chromosome 6A, 611, and 5B of dicoccoides resulted in greater increase in Zn and Fe concentration when compared to their recipient parent and to other chromosome substitution lines. The results indicate that Triticum turgidum L. var. dicoccoides (wild emmer) is an important genetic resource for increasing concentration and content of Zn and Fe in modern cultivated wheat.

Biofortification and localization of zinc in wheat grain.

Zinc (Zn) deficiency associated with low dietary intake is a well-documented public health problem, resulting in serious health and socioeconomic problems. Field experiments were conducted with wheat to test the role of both soil and foliar application of ZnSO4 in Zn concentration of whole grain and grain fractions (e.g., bran, embryo and endosperm) in 3 locations. Foliar application of ZnSO4 was realized at different growth stages (e.g., stem elongation, boot, milk, dough stages) to study the effect of timing of foliar Zn application on grain Zn concentration. The rate of foliar Zn application at each growth stage was 4 kg of ZnSO4·7H2O ha(-1). Laser ablation (LA)-ICP-MS was used to follow the localization of Zn within grain. Soil Zn application at a rate of 50 kg of ZnSO4·7H2O ha(-1) was effective in increasing grain Zn concentration in the Zn-deficient location, but not in the locations without soil Zn deficiency. In all locations, foliar application of Zn significantly increased Zn concentration in whole grain and in each grain fraction, particularly in the case of high soil N fertilization. In Zn-deficient location, grain Zn concentration increased from 11 mg kg(-1) to 22 mg kg(-1) with foliar Zn application and to 27 mg kg(-1) with a combined application of ZnSO4 to soil and foliar. In locations without soil Zn deficiency, combination of high N application with two times foliar Zn application (e.g., at the booting and milk stages) increased grain Zn concentration, on average, from 28 mg kg(-1) to 58 mg kg(-1). Both ICP-OES and LA-ICP-MS data showed that the increase in Zn concentration of whole grain and grain fractions was pronounced when Zn was sprayed at the late growth stage (e.g., milk and dough). LA-ICP-MS data also indicated that Zn was transported into endosperm through the crease phloem. To our knowledge, this is the first study to show that the timing of foliar Zn application is of great importance in increasing grain Zn in wheat, especially in the endosperm part that is the predominant grain fraction consumed in many countries. Providing a large pool of Zn in vegetative tissues during the grain filling (e.g., via foliar Zn spray) is an important practice to increase grain Zn and contribute to human nutrition.

EFFECTS OF ZINC FERTILIZATION ON GRAIN YIELD AND SHOOT CONCENTRATIONS OF ZINC, BORON, AND PHOSPHORUS OF 25 WHEAT CULTIVARS GROWN ON A ZINC-DEFICIENT AND BORON-TOXIC SOIL

Field experiments were carried out to study the grain yield, shoot concentrations of zinc (Zn), boron (B) and phosphorus (P), and tolerance to Zn deficiency of 21 bread wheat (Triticum aestivum) and four durum wheat (Triticum durum) cultivars grown in a B-toxic and Zn-deficient calcareous soil in Central Anatolia with (+Zn = 23 kg Zn ha−1) and without Zn fertilization in 1993–1994 and 1994–1995 cropping seasons. Tolerance to Zn deficiency (Zn efficiency ratio) was measured by considering the ratio of grain yield under Zn deficiency to that with Zn fertilization. Zinc fertilization significantly increased grain yield of all cultivars in both years. On average, increases in grain yield of 25 wheat cultivars by Zn fertilization were 37% in the first and 40% in the second year. When results of the 2 cropping seasons were averaged, Zn efficiency ratios of the cultivars ranged from 40% to 84%, with an average of 62%. Despite large genotypic variation in Zn efficiency, shoot Zn concentrations under Zn-deficient conditions did not differ among Zn-efficient and Zn-inefficient cultivars. There were large differences in B concentration in shoots of cultivars under both Zn deficiency and Zn fertilization. However, on average for 25 wheat cultivars, Zn fertilization did not influence B concentration. In contrast to B, Zn fertilization consistently decreased shoot concentration of P in all cultivars. The results presented show that wheat cultivars growing in Zn-deficient and B-toxic soil conditions vary considerably in their grain yield, and these differences were not related to the shoot concentrations of Zn and B. Nevertheless, for many cultivars there was a close relationship between tolerance to Zn deficiency and tolerance to B toxicity. This relationship was discussed in terms of high Zn efficiency-enhanced tissue tolerance to B toxicity.

Differences in Shoot Boron Concentrations, Leaf Symptoms, and Yield of Turkish Barley Cultivars Grown on Boron‐Toxic Soil in Field

Abstract Using 10 barley Turkish cultivars (Hordeum vulgare L.) field experiments were carried out on soils containing normal and very high soluble boron (B) concentration to study genotypic variation in tolerance to B toxicity in soil and the relationships between the shoot or leaf concentrations of B, severity of B‐toxicity symptoms and yield. As judged by differences in degree of severity of B‐toxicity symptoms on leaves and in reduction of shoot dry weight or grain yield there was a substantial genotypic variation in tolerance to B toxicity in soil. Among the barley cultivars examined Hamidiye and Bülbül were the most sensitive, and Anadolu and Tarm‐92 the most tolerant. The differences in tolerance to B toxicity showed a very close relationship to the severity of B‐toxicity symptoms, but not at all to shoot or leaf concentrations of B. Despite the distinct differences in sensitivity to B toxicity, B‐tolerant, and B‐sensitive cultivars had very similar tissue concentrations of B, and even the most B‐sensitive cultivar, Hamidiye contained the lowest B concentration in flag leaves. Shoot dry weight of the cultivars at the tillering stage corresponded well to the grain yields. These results suggested that the symptom scoring for B toxicity symptoms and shoot dry weight at early stage of growth can be considered as reliable criteria for screening cultivars for tolerance to B toxicity in soils. In view of the results obtained in the present study one may speculate that internal mechanisms play a decisive role in expression of differential tolerance to B toxicity in field‐grown barley cultivars.

K+ Efflux and Retention in Response to NaCl Stress Do Not Predict Salt Tolerance in Contrasting Genotypes of Rice (Oryza sativa L.)

Sudden elevations in external sodium chloride (NaCl) accelerate potassium (K+) efflux across the plasma membrane of plant root cells. It has been proposed that the extent of this acceleration can predict salt tolerance among contrasting cultivars. However, this proposal has not been considered in the context of plant nutritional history, nor has it been explored in rice (Oryza sativa L.), which stands among the world’s most important and salt-sensitive crop species. Using efflux analysis with 42K, coupled with growth and tissue K+ analyses, we examined the short- and long-term effects of NaCl exposure to plant performance within a nutritional matrix that significantly altered tissue-K+ set points in three rice cultivars that differ in salt tolerance: IR29 (sensitive), IR72 (moderate), and Pokkali (tolerant). We show that total short-term K+ release from roots in response to NaCl stress is small (no more than 26% over 45 min) in rice. Despite strong varietal differences, the extent of efflux is shown to be a poor predictor of plant performance on long-term NaCl stress. In fact, no measure of K+ status was found to correlate with plant performance among cultivars either in the presence or absence of NaCl stress. By contrast, shoot Na+ accumulation showed the strongest correlation (a negative one) with biomass, under long-term salinity. Pharmacological evidence suggests that NaCl-induced K+ efflux is a result of membrane disintegrity, possibly as result of osmotic shock, and not due to ion-channel mediation. Taken together, we conclude that, in rice, K+ status (including efflux) is a poor predictor of salt tolerance and overall plant performance and, instead, shoot Na+ accumulation is the key factor in performance decline on NaCl stress.

X-ray fluorescence microscopy of zinc localization in wheat grains biofortified through foliar zinc applications at different growth stages under field conditions

AimBiofortification of wheat with zinc (Zn) through foliar Zn application has been proposed as an agronomic strategy to increase grain Zn concentration, which could serve as a nutritional intervention in regions with dietary Zn deficiency.MethodsBread wheat (Triticum aestivum L.) was biofortified through foliar Zn applications at different growth stages. The concentration of Zn and associated micronutrient in harvested whole grains was determined by ICP-OES. Synchrotron-based X-ray fluorescence microscopy (XFM) was then used to investigate the localization of Zn and associated micronutrients in cross sections of these grains.ResultsThe concentration of Zn and other micronutrients (Mn, Fe, and Cu) was higher in grains treated with foliar Zn during grain-filling (early milk/dough) than those treated at stem elongation. The increase in Zn concentration of wheat grain with foliar application during grain-filling can be attributed to the intense localization of Zn in the aleurone layer, modified aleurone, crease tissue, vascular bundle, and endosperm cavity, and to a modest localization in endosperm, which is the most dominant grain tissue. These tissues and the Zn they contain are presumed to remain after milling and can potentially increase the Zn concentration in wheat flour.ConclusionsBy using XFM, it was shown that foliar Zn spray represents an important agronomic tool for a substantial Zn enrichment of different fractions of wheat grain, especially the endosperm. Further investigation of the chemical speciation of Zn in the endosperm is recommended to assess Zn bioavailability in harvested whole grain of wheat that has been biofortified through different timing of foliar Zn application.