Yusuf Genc

Selenium increases seed production in Brassica

Selenium (Se) is essential for humans and animals but is not considered to be essential for higher plants. Although researchers have found increases in vegetative growth due to fertiliser Se, there has been no definitive evidence to date of increased reproductive capacity, in terms of seed production and seed viability. The aim of this study was to evaluate seed production and growth responses to a low dose of Se (as sodium selenite, added to solution culture) compared to very low-Se controls in fast-cycling Brassica rapa L. Although there was no change in total biomass, Se treatment was associated with a 43% increase in seed production. The Se-treated Brassica plants had higher total respiratory activity in leaves and flowers, which may have contributed to higher seed production. This study provides additional evidence for a beneficial role for Se in higher plants.

Sodium exclusion QTL associated with improved seedling growth in bread wheat under salinity stress

Worldwide, dryland salinity is a major limitation to crop production. Breeding for salinity tolerance could be an effective way of improving yield and yield stability on saline-sodic soils of dryland agriculture. However, this requires a good understanding of inheritance of this quantitative trait. In the present study, a doubled-haploid bread wheat population (Berkut/Krichauff) was grown in supported hydroponics to identify quantitative trait loci (QTL) associated with salinity tolerance traits commonly reported in the literature (leaf symptoms, tiller number, seedling biomass, chlorophyll content, and shoot Na+ and K+ concentrations), understand the relationships amongst these traits, and determine their genetic value for marker-assisted selection. There was considerable segregation within the population for all traits measured. With a genetic map of 527 SSR-, DArT- and gene-based markers, a total of 40 QTL were detected for all seven traits. For the first time in a cereal species, a QTL interval for Na+ exclusion (wPt-3114-wmc170) was associated with an increase (10%) in seedling biomass. Of the five QTL identified for Na+ exclusion, two were co-located with seedling biomass (2A and 6A). The 2A QTL appears to coincide with the previously reported Na+ exclusion locus in durum wheat that hosts one active HKT1;4 (Nax1) and one inactive HKT1;4 gene. Using these sequences as template for primer design enabled mapping of at least three HKT1;4 genes onto chromosome 2AL in bread wheat, suggesting that bread wheat carries more HKT1;4 gene family members than durum wheat. However, the combined effects of all Na+ exclusion loci only accounted for 18% of the variation in seedling biomass under salinity stress indicating that there were other mechanisms of salinity tolerance operative at the seedling stage in this population. Na+ and K+ accumulation appear under separate genetic control. The molecular markers wmc170 (2A) and cfd080 (6A) are expected to facilitate breeding for salinity tolerance in bread wheat, the latter being associated with seedling vigour.

A simple method to evaluate genetic variation in grain zinc concentration by correcting for differences in grain yield

Increasing the grain zinc (Zn) concentration of staple food crops will help alleviate chronic Zn deficiency in many areas of the world. Significant variation in grain Zn concentration is often reported among collections of cereals, but frequently there is a concomitant variation in grain yield. In such cases grain Zn concentration and grain yield are often inversely related. Without considering the influence of the variation in grain yield on Zn concentration, the differences in grain Zn concentration may simply represent a yield dilution effect. Data from a series of field and glasshouse experiments was used to illustrate this effect and to describe an approach that will overcome the yield dilution effect. In experiments with a wide range of bread wheat, synthetic hexaploids and accessions of durum wheat, variation in grain yield among the genotypes accounted for 30–57% of the variation in grain Zn concentration. Variation in kernel weight also occurred, but was poorly correlated with grain Zn concentration. To account for the influence of variation in grain yield on grain Zn concentration grain Zn yield was plotted against grain yield. By defining the 95% confidence belt for the regression genotypes that have inherently low or high grain Zn concentrations at a given yield level can be identified. This method is illustrated using two data sets, one consisting of bread wheat and one comprising a collection of synthetic hexaploids.

Phosphate Utilization Efficiency Correlates with Expression of Low-Affinity Phosphate Transporters and Noncoding RNA, IPS1, in Barley

Genetic variation in phosphorus (P) efficiency exists among wheat (Triticum aestivum) and barley (Hordeum vulgare) genotypes, but the underlying mechanisms for the variation remain elusive. High- and low-affinity phosphate (Pi) PHT1 transporters play an indispensable role in P acquisition and remobilization. However, little is known about genetic variation in PHT1 gene expression and association with P acquisition efficiency (PAE) and P utilization efficiency (PUE). Here, we present quantitative analyses of transcript levels of high- and low-affinity PHT1 Pi transporters in four barley genotypes differing in PAE. The results showed that there was no clear pattern in the expression of four paralogs of the high-affinity Pi transporter HvPHT1;1 among the four barley genotypes, but the expression of a low-affinity Pi transporter, HvPHT1;6, and its close homolog HvHPT1;3 was correlated with the genotypes differing in PUE. Interestingly, the expression of HvPHT1;6 and HvPHT1;3 was correlated with the expression of HvIPS1 (for P starvation inducible; noncoding RNA) but not with HvIPS2, suggesting that HvIPS1 plays a distinct role in the regulation of the low-affinity Pi transporters. In addition, high PUE was found to be associated with high root-shoot ratios in low-P conditions, indicating that high carbohydrate partitioning into roots occurs simultaneously with high PUE. However, high PUE accompanying high carbon partitioning into roots could result in low PAE. Therefore, the optimization of PUE through the modification of low-affinity Pi transporter expression may assist further improvement of PAE for low-input agriculture systems.

Selenium distribution in wheat grain, and the effect of postharvest processing on wheat selenium content

Selenium (Se) is an essential micronutrient for animals and humans, and wheat is a major dietary source of this element. It is improtant that postharvest processing losses of grain Se are minimized. This study, using grain dissection, milling with a Quadrumat mill, and baking and toasting studies, investigated the distribution of Se and other mineral nutrients in wheat grain and the effect of postharvest processing on their retention. The dissection study, although showing Se concentration to be highest in the embryo, confirmed (along with the milling study) previous findings that Se (which occurs mostly as selenomethionine in wheat grain) and S are more evenly distributed throughout the grain when compared to other mineral nutrients, and hence, lower proportions are removed in the milling residue. Postmilling processing did not affect Se concentration or content of wheat products in this study.No genotypic variability was observed for grain distribution of Se in the dissection and milling studies, in contrast to Cu, Fe., Mn, and Zn. This variability could be exploited in breeding for higher proportions of these nutrients in the endosperm to make white flour more nutritious. Further research could include grain dissection and milling studies using larger numbers of cultivars that have been grown together and a flour, extraction rate of around 70%

HvZIP7 mediates zinc accumulation in barley (Hordeum vulgare) at moderately high zinc supply

High expression of zinc (Zn)-regulated, iron-regulated transporter-like protein (ZIP) genes increases root Zn uptake in dicots, leading to high accumulation of Zn in shoots. However, none of the ZIP genes tested previously in monocots could enhance shoot Zn accumulation. In this report, barley (Hordeum vulgare) HvZIP7 was investigated for its functions in Zn transport. The functions of HvZIP7 in planta were studied using in situ hybridization and transient analysis of subcellular localization with a green fluorescent protein (GFP) reporter. Transgenic barley lines overexpressing HvZIP7 were also generated to further understand the functions of HvZIP7 in metal transport. HvZIP7 is strongly induced by Zn deficiency, primarily in vascular tissues of roots and leaves, and its protein was localized in the plasma membrane. These properties are similar to its closely related homologs in dicots. Overexpression of HvZIP7 in barley plants increased Zn uptake when moderately high concentrations of Zn were supplied. Significantly, there was a specific enhancement of shoot Zn accumulation, with no measurable increase in iron (Fe), manganese (Mn), copper (Cu) or cadmium (Cd). HvZIP7 displays characteristics of low-affinity Zn transport. The unique function of HvZIP7 provides new insights into the role of ZIP genes in Zn homeostasis in monocots, and offers opportunities to develop Zn biofortification strategies in cereals.

CRITICAL DEFICIENCY CONCENTRATION OF ZINC IN BARLEY GENOTYPES DIFFERING IN ZINC EFFICIENCY AND ITS RELATION TO GROWTH RESPONSES

A growth room study was conducted to compare responses to zinc of two barley (Hordeum vulgare L. cw. Tarm and Hamidiye) genotypes differing in zinc (Zn) efficiency and to determine a critical deficiency concentration of Zn in tissue. Two genotypes of barley, Tarm (Zn efficient) and Hamidiye (Zn inefficient), were grown in a Zn deficient siliceous sand with Zn added at 10 Zn rates (0, 0.04, 0.08, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, and 6.4 mg Zn/kg dry soil). Visual Zn deficiency symptoms, such as inhibition of shoot elongation and development of chlorotic areas on leaves, appeared more rapidly and severely in Hamidiye when Zn supply was deficient ( < 0.08 mg/kg), while those symptoms in Tarm were slightly visible only when no Zn was applied. Tarm had greater shoot and root dry matter than Hamidiye until Zn fertilization reached 0.8mg/kg fertilization rate at which both genotypes achieved their maximal growth. Beyond this rate, both genotypes had similar yields. Zn concentration and content were increased progressively by Zn fertilization, but significant genetic differences occurred only in Zn content under severe Zn deficiency (0.04 mg/kg). Similarly, Zn concentration in youngest emerged leaf blades (YEBs) increased as a result of Zn fertilization; however, there was no significant genotypic difference. The critical deficiency concentration of Zn estimated by Mitscherlich plant growth model was similar for both genotypes (20 mg Zn/kg DW).The results demonstrated that under Zn deficiency, Tarm and Hamidiye exhibited a differential response to Zn fertilization. The greater efficiency of Tarm over Hamidiye may be attributed to its higher uptake of Zn from the soil and more efficient utilization at a cellular level. The differences found in the field between the two genotypes were expressed in visual symptoms, dry matter production, Zn efficiency, and Zn content in shoots under controlled conditions, suggesting that these parameters can be used as criteria when assessing for tolerance to Zn deficiency. The results also established a good correlation between Zn concentration in the YEBs and plant growth, indicating that critical deficiency concentration can be used as a reference point in the assessment of Zn status in barley.

Effect of seed zinc content on early growth of barley (Hordeum vulgare L.) under low and adequate soil zinc supply

Worldwide, barley is often grown on zinc (Zn) deficient soils. Screening for varieties tolerant of low soil Zn (Zn-efficient varieties) generally involves assessing growth or yield of plants grown at different levels of Zn supply. Seed nutrient reserves can influence the growth of the plant; however, there have been no reports on the effect of seed Zn content on the growth of barley. In 2 experiments, we studied the effect of seed Zn content on early growth of barley in 2 genotypes, Amagi Nijo and Tantangara. In Expt 1, the amounts of Zn in the seed ranged from 0.4 to 0.7 μg/seed, whereas in Expt 2, seed Zn ranged from 0.7 to 5.0 μg/seed. The plants were grown in a Zn-defi- cient siliceous sand with Zn added at 0, 0.04, 0.2, 0.8, and 3.2 mg Zn/kg soil in Expt 1 and at 0, 0.04, and 0.8 mg Zn/kg soil in Expt 2, and harvested at tillering. Growth and expression of visual symptoms were measured. Plants grown from seed with low Zn content developed symptoms of Zn deficiency by the 2-leaf stage in soil with no soil-applied Zn. Symptoms were reduced markedly as seed Zn content increased. Shoot and root growth increased as the amount of Zn in seed increased, but the effect was most evident when soil Zn supply was limiting plant growth (#0.04 mg Zn/kg soil). For instance, when no Zn was added to the soil, shoot dry weight of plants grown from high-Zn seed was 108% greater than that of plants grown from low-Zn seed, whereas at 0.04 and 0.8 mg Zn/kg soil, the increases were only 52% and 18%, respectively. Soil Zn application significantly increased tissue Zn concentrations. However, the effect of seed Zn content on tissue Zn concentrations was significant only at very high levels of seed Zn. The results presented showed that seed Zn improves vegetative growth in barley, especially when Zn supply is deficient for plant growth. Seed Zn content also affected the determination of Zn efficiency of genotypes, and comparisons of dry matter production of seedlings grown from seed with a wide range in Zn content may alter their rankings for Zn efficiency as determined in this pot assay. The results indicate that seed of similar Zn content needs to be used when comparing genotypes for determination of Zn efficiency. Additional keywords: Zn deficiency, Zn efficiency.

The Use of Hydroponics in Abiotic Stress Tolerance Research

Hydroponics, the ‘water culture’ of plants, has been used in both research and commercial contexts since the 18th century. Although now used successfully on a large scale by commercial growers of fast-growing horticultural crops such as lettuce, strawberries, tomatoes, and carnations, hydroponics was initially developed as a part of early research into plant nutrition. The idea of hydroponics, its development and improvement, stimulated the interest of plant biologists, and their research provided useful outcomes and scientific knowledge about mechanisms of nutritional toxicity/deficiency and plant development in general. Scientists discovered that plants required only a small number of inorganic elements, in addition to water, oxygen and sunlight, to grow. It was later realised that plants grew better hydroponically if the solutions were aerated. The use of hydroponics enabled plant scientists to identify which elements were essential to plants, in what ionic forms, and what the optimal concentrations of these elements were. It allowed them to easily observe the effects of elemental deficiencies and toxicities and to study other aspects of plant development under more controlled conditions. As scientists’ understanding of the requirements for growing plants in hydroponics increased, the system was adopted and refined by commercial producers who found it allowed them to control environmental variables and deliver higher yields of product more reliably. Hydroponics systems are now operated in temperatureand light-controlled glasshouses which allow crop production through all seasons.

A soil-based method to screen for zinc efficiency in seedlings and its ability to predict yield responses to zinc deficiency in mature plants

Nutrient efficiency measures the ability of a plant to grow and produce grain when the availability of a nutrient is low. Seedling tests for nutrient efficiency will be most useful if the results correlate well with grain yield responses. In two experiments, a diverse range of barley genotypes was screened for zinc (Zn) efficiency at the seedling stage and the relationship between vegetative and grain measures of Zn efficiency was examined. In Expt 1, 54 barley and 4 wheat genotypes were grown at 2 levels of Zn (0.02 and 0.8 mg/kg soil) for 21 days. Zinc efficiency ranged from 18% to 52%. The visual symptoms of Zn deficiency varied considerably between genotypes and was significantly correlated with Zn efficiency. Root:shoot ratio was increased by Zn deficiency and varied between genotypes, but these differences were not related to Zn efficiency. Zinc concentration and especially Zn content at 0.02 mg Zn/kg were significantly related to Zn efficiency. In Expt 2, 15 genotypes, selected on the basis of their response in Expt 1, were grown to maturity at either 0.1 mg Zn/kg or 2.4 mg Zn/kg. Zn efficiency, based on relative grain yield, ranged from 5% to 54%. High efficiency was associated with a large number of grains per plant and high kernel weight. Rankings of Zn efficiency in the experiment were significantly correlated with the rankings for visual scores in Expt 1. The 2 experiments suggested that deficiency symptoms at the seedling stage can identify efficient genotypes and could be useful for routine screening for Zn efficiency. Independent data from multisite comparisons over 8 years were used to examine the long-term performance of efficient and inefficient genotypes in the field. Hierarchical cluster was used to define efficient and inefficient groupings within the 56 genotypes examined in Expt 1, based on their responses to Zn. The Zn-efficient genotypes tended to yield more than the Zn-inefficient genotypes. The data provide prima facae evidence that high Zn efficiency may contribute to improved adaptation of barley in South Australia.