Zdenko Rengel

Wheat genotypes differ in Zn efficiency when grown in chelate-buffered nutrient solution. I: Growth

Ten Triticum aestivum and two Triticum turgidum conv. durum genotypes were grown in chelate-buffered nutrient solution at Zn supplies ranging from deficient to sufficient (free Zn activities from 2 to 200 pM, pZn from 11.7 to 9.7). The critical level of Zn ion activity in solution for healthy growth of wheat plants was around 40 pM. Genotypes differed in the growth response: those classified as Zn-efficient suffered less reduction of shoot growth and did not change the rate of root growth at a Zn supply quite deficient for Zn-inefficient genotypes. Root growth of Zn-inefficient genotypes increased at deficient Zn supply. The shoot/root ratio was the most sensitive parameter of Zn efficiency; Zn-efficient genotypes showed less reduction in the ratio when grown at deficient compared to sufficient Zn supply. Classification of wheat genotypes into Zn-efficient and Zn-inefficient groups after screening in chelate-buffered nutrient solution corresponded well with classification obtained in field experiments on Zn-deficient soil.

Importance of seed Zn content for wheat growth on Zn-deficient soil

Two wheat (Triticum aestivum L.) genotypes (Zn-efficient Excalibur and Zn-inefficient Gatcher) were grown from low-Zn (around 250 ng Zn/seed) and high-Zn seed (around 700 ng Zn/seed) in a Zn-deficient siliceous sand fertilised with 0, 0.05, 0.2, 0.8 or 3.2 mg Zn kg-1 soil. At maturity, plants derived from the high-Zn seed had bigger grains and produced more grains than plants grown from the low-Zn seed when fertilised with nil Zn. Plants grown from high-Zn seed produced more grain dry matter per unit of Zn absorbed by the above-ground parts, transported a larger proportion of absorbed Zn to the grain, and approached the maximum harvest index with the fertilisation rate of 0.05 mg Zn kg-1 compared to 0.2 mg Zn kg-1 soil required for plants derived from the low-Zn seed. The Zn-efficient cv. Excalibuir had greater fertiliser efficiency when fertilised with 0.05 mg Zn kg-1 soil and a greater harvest index at nil Zn treatment compared to the Zn-inefficient cv. Gatcher. Zn-deficient plants produced seed with higher concentrations of all inorganic nutrients determined except Zn. There was a positive relationship between grain dry weight and Zn concentrations in youngest expanded blades sampled at 6 weeks of growth. It is concluded that crops grown from seed containing higher Zn content have a distinct advantage which culminates in greater yield when grown in soils of low Zn status.

Root morphology of wheat genotypes differing in zinc efficiency

Abstract The root morphology (root length, diameter) of the three wheat genotypes (Triticum aestivum L. cvs Excalibur and Gatcher, and T. turgidum conv. durum (Desf.) McKay cv Durati) grown in zinc (Zn)‐deficient, sandy soil under controlled conditions has been measured by a root scanner coupled to a computer. Wheat plants were supplied with 0, 0.025, 0.05, 0.1, 0.2, or 0.4 mg Zn/kg soil. Excalibur has previously been identified as the Zn‐efficient genotype which can take up more Zn and has higher yield in soils with low plant‐available Zn. Durati is Zn‐inefficient and Gatcher an intermediate genotype with respect to Zn efficiency. Root and shoot dry matter significantly increased at 0.1 mg Zn/kg soil compared to the 0 Zn level. Zinc content in shoots was lower in Durati than in Excalibur and Gatcher at sufficient supply of Zn. Zinc applications had no significant effect on root morphology at two weeks after sowing. At that time, however, the Zn‐efficient genotype Excalibur developed a longer and thinner ...

Carbonic Anhydrase Activity in Leaves of Wheat Genotypes Differing in Zn Efficiency

Summary Activity of carbonic anhydrase (CA) (EC 4.2.1.1) was determined in leaf extracts of two wheat genotypes ( Triticum aestivum L., cv. Warigal, and T. turgidum L. conv. durum (Desf.) MacKey, cv. Durati) differing in Zn efficiency. Generally, CA activity decreased with plant age in both genotypes. Under sufficient Zn supply, the two genotypes had the same CA activity; under Zn deficiency, however, a 2-fold higher CA activity was recorded for Zn-efficient Warigal than for Zn-inefficient Durati. When Zn-sufficient plants were transferred into solutions with low Zn supply, plants of the cv. Durati lost a greater portion of CA activity than those of the cv. Warigal. Upon re-supply of Zn to the Zn-deficient plants, Durati lost an ability to increase CA activity, while Warigal showed a saturating, curvilinear increase in CA activity under the same conditions. For any given Zn concentration in leaf tissue, Zn-efficient Warigal showed greater CA activity than Zn-inefficient Durati. An ability of Zn-efficient wheat genotypes to maintain greater CA activity under Zn deficiency may be beneficial in maintaining the photosynthetic rate and dry matter production at a higher level, a characteristic that may be especially important for wheat as a species with inherently lower CA activity compared to other species.

Mechanistic simulation models of nutrient uptake: A review

Mechanistic models of nutrient uptake consider diffusion and mass flow acting simultaneously to supply nutrients to the sorbing root surface. Plant parameters that determine nutrient uptake include those describing changes in root geometry and size due to root growth and others describing kinetics of the nutrient uptake process. Mechanistic models generally assume that nutrient uptake occurs evenly along the roots that are uniformly distributed in homogeneous and isotropic soil having no temporal and spatial gradients in volumetric moisture content. Uptake of immobile nutrients (like P and K) is mainly determined by the soil-supply parameters and is well predicted by the simulation models. In contrast, uptake of mobile nutrients (e.g. Ca and Mg) that usually accumulate at the root surface is determined mainly by the plant-uptake parameters; prediction of uptake of those nutrients is subject to a much wider error due to uncertainties of applying kinetic parameters measured on hydroponically-grown plants to soil-grown plants. Comparison of model-predicted and experimentally-observed uptake values should be done by calculating the mean squares of deviates instead of performing regression analysis, especially if data that encompass a relatively wide range in root length are considered. Complementary-ion effects occurring at the soil-root interface raise the need for developing a multi-nutrient uptake model that will simultaneously calculate uptake of several essential nutrients taking into account interactions among them.

Genotypic variation in zinc efficiency and resistance to crown rot disease (Fusarium graminearum Schw. Group 1) in wheat

A crown rot disease in wheat caused by the fungusFusarium graminearum Schw. Group 1 is a widespread problem in chronically Zn-deficient Australian soils. A link between crown rot and Zn deficiency was established by Sparrow and Graham (1988). This paper reports a test of a further hypothesis, that wheat genotypes more efficient at extracting zinc from low-zinc soils are more resistant to infection by this pathogen. Three wheat cultivars (Excalibur, Songlen and Durati) of differential Zn efficiency were tested at three zinc levels (0.05, 0.5 and 2.0 mg Zn kg−1 of soil) and three levels ofF. graminearum S. Group 1 inoculum (0.1 g and 0.3 g kg−1 live chaff-inoculum and control having 0.1 g kg−1 dead chaff inoculum). Six weeks after sowing dry matter production of shoots and roots was decreased byFusarium inoculation at 0.05 mg and 0.5 mg kg−1 applied Zn.Fusarium inoculum at 0.1 g was as effective as 0.3 g kg−1 for infection and decreasing dry matter. The infection at the basal part of culm decreased significantly by increasing the rate of Zn application. Excalibur, a Zn-efficient cultivar (tolerant to Zn deficiency) produced significantly more shoot and root dry matter, and showed less disease infection compared with Zn-inefficient cultivars (Durati and Songlen) at low (0.05 mg Zn kg−1 soil) and medium (0.5 mg Zn kg−1 soil) Zn fertilization rates. Higher rate of Zn fertilization (2.0 mg Zn kg−1 soil) reduced the disease level in Durati to the level of Excalibur but the disease level of Songlen was still high, indicating its high Zn requirement and or sensitivity to crown rot. The data on Zn uptake show that Excalibur, being Zn-efficient, was able to scavenge enough Zn from Zn-deficient soil, we suggest that besides sustaining growth Excalibur was able to build and maintain resistance to the pathogen; inefficient cultivars needed extra Zn fertilization to achieve performance comparable to that of Excalibur. The present study indicates that growing Zn-efficient cultivars of wheat along with judicious use of Zn fertilizer in Zn-deficient areas where crown rot is a problem may sustain wheat production by reducing the severity of the disease as well as by increasing the plant vigour through improved Zn nutrition. ei]Section editor: R Rodriques-Kalana

Manganese nutrition and accumulation of phenolics and lignin as related to differential resistance of wheat genotypes to the take-all fungus

Differential resistance of four Triticum aestivum L. genotypes to isolates of take-all fungus (Gaeuman-nomyces graminis var. ritici Walker) was tested in a complete factorial experiment set up in a growth chamber using Mn-deficient Wangary sand amended with four rates of Mn. Mn-efficient cultivars produced more dry matter at low supply of Mn. Fertilization with Mn significantly increased its accumulation in roots and shoots. The most sensitive measure of take-all infection was the total length of root stellar lesions; these lesions were reduced by Mn fertilization and were shorter in Mn-efficient genotypes. The resistance-enhancing effect of Mn was the most obvious in the Mn-inefficient genotype (Bayonet) and the least obvious in the Mn-efficient one (C8MM). Phenolics biosynthesis in roots was clicited by fungal infection, especially in the case of the highly virulent isolate. The weakly virulent isolate increased phenolics concentration in roots much more if no Mn was added, indicating that the resistance-enhancing effect of Mn may not be directly exerted through the effects on phenolics biosynthesis. Lignin concentration in roots decreased due to Mn fertilization, while no effect of take-all infection was noted. It appears that biosynthesis of phenolics and lignin in wheat roots has a low Mn requirement which can be satisfied at environmental Mn concentrations below those necessary for optimum plant growth. ei]Section editor: A C Borstlap ei]Section editor: H Lambers

Transmembrane calcium fluxes during Al stress

The primary Al lesion is suggested to be blockage of the root plasma membrane Ca2+ channels. Resulting decrease in net Ca2+ uptake into the root tip cells leads to Ca2+ deficiency in the cytoplasm and disturbance of the cell Ca2+ homeostasis, effects that can deleteriously influence cell structure and function. Contribution of internal Ca2+ stores to maintaining cytoplasmic Ca2+ concentration at physiological levels is considered to be insufficient in meristematic cells at the root tip. It is suggested that differential blockage of Ca2+ channels may be at the core of differential tolerance to Al, opening up the possibility of manipulating Al tolerance at the molecular level.

Effects of Al, rare earth elements, and other metals on net 45Ca2+ uptake by Amaranthus protoplasts

Summary Aluminium has recently been shown to interfere with Ca 2+ influx into Amaranthus protoplasts by binding to the verapamil-specific site and thus blocking Ca 2+ channels. To further elucidate the mechanism of Al-related blockage of Ca 2+ channels, short-term net 45 Ca 2+ uptake by Amaranthus tricolor protoplasts was monitored from uptake media prepared to test the influence of pH, Al and various other metal ions. Gadolinium and lanthanum (well-known Ca 2+ -channel blockers) appeared to be more powerful inhibitors of net Ca 2+ uptake than Al at both pH levels tested (4.5 and 5.5). Aluminium counteracted the inhibition due to La. No interaction was noted between Al and Gd. Another rare earth element tested, cerium, showed the same pattern of inhibition of net Ca 2+ uptake regardless of the presence or absence of Al at both pH values. Compared to Al, several other metals known to inhibit root growth and elongation (rhizotoxicity is also an early symptom of Al stress) were either less inhibitory to net Ca 2+ uptake [indium and especially chromium (III)] or did not affect net Ca 2+ uptake at all (scandium).

Aiuminium tolerance of durum wheat germplasm

SummaryAluminium tolerance of Macedonian durum wheat (Triticum turgidum L. conv. durum (Desf.) MacKey) germplasm was evaluated in nutrient solutions containing 0, 74 or 148 μM of total Al. Relative root length (148 μM Al/0 Al) of various genotypes ranged from 41 to 72% (from moderately sensitive to moderately tolerant to Al). No genotype with Al tolerance close to that of very tolerant T. aestivum cultivar Atlas-66 was found. Seed Ca concentration was positively (r=0.64, P≤0.05) and seed Fe concentration negatively (r=−0.71, P≤0.05) related to the relative root growth. Such a significant correlation was not obtained for seed concentrations of other nutrients or seed protein content.