Dry matter production and distribution of zinc in bread and durum wheat genotypes differing in zinc efficiency

Six bread wheat (Triticum aestivum cvs. Kiraç-66, Gerek-79, Aroona, ES 91-12, ES-14 and Kirkpinar) and four durum wheat (Triticum durum cvs. BDMM-19, Kunduru-1149, Kiziltan-91 and Durati) genotypes were grown under controlled environmental conditions in nutrient solution for 20 days to study the effect of varied supply of Zn (0 to 1 µM) on Zn deficiency symptoms in shoots, root and shoot dry matter production, and distribution of Zn in roots and shoots.Visual Zn deficiency symptoms, such as whitish-brown lesions on leaves, appeared rapidly and severly in durum wheats, particularly in Kiziltan-91 and Durati. Among the durum wheats, BDMM-19 was less affected by Zn deficiency, and among the bread wheats Kiraç-66, ES 91-12, Aroona and Gerek-79 were less affected than ES-14 and Kirkpinar.Under Zn deficiency, shoot dry matter production was decreased in all genotypes, but more distinctly in durum wheat genotypes. Despite severe decreases in shoot growth, root growth of all genotypes was either not affected or even increased by Zn deficiency. Correspondingly, shoot/root dry weight ratios were lower in Zn-deficient than in Zn-sufficient plants, especially in durum wheat genotypes.The distinct differences among the genotypes in sensitivity to Zn deficiency were closely related with the Zn content (Zn accumulation) per shoot but not with the Zn concentration in the shoot dry matter. On average, genotypes with lesser deficiency symptoms contained about 42% more Zn per shoot than genotypes with severe deficiency symptoms. In contrast to shoots, the Zn content in roots did not differ between genotypes. Shoot/root ratios of total Zn content were therefore greater for genotypes with lesser deficiency symptoms than for genotypes with severe deficiency symptoms (i.e. all durum wheat genotypes).The results suggest that the enhanced capacity of genotypes for Zn uptake and translocation from roots to shoot meristems under deficient Zn supply might be the most important factor contributing to Zn efficiency in wheat genotypes. The results also demonstrate that under severe Zn deficiency, Zn concentration in the shoot dry matter is not a suitable parameter for distinguishing wheat genotypes in their sensitivity to Zn deficiency.     

Light-mediated release of phytosiderophores in wheat and barley under iron or zinc deficiency

The effect of varied light intensity (50 – 600 mol m-2 s-1) on the rate of phytosiderophore release was studied under zinc (Zn) deficiency using a bread (Triticum aestivum L. cv. Aroona) and a durum wheat cultivar (Triticum durum Desf. cv. Durati) differing in zinc (Zn) efficiency and under iron (Fe) deficiency using a barley cultivar (Hordeum vulgare L. Europe). Plants were grown under controlled environmental conditions in nutrient solution for 15 days (wheat plants) or 11 days (barley plants). Phytosiderophore release was determined by measuring capacity of root exudates to mobilize copper (Cu) from a Cu-loaded resin.With increasing light intensity visual Zn deficiency symptoms such as whitish-brown lesions on leaf blade developed rapidly and severely in wheat, particularly in the durum cultivar Durati. In wheat plants supplied well with Zn, increases in light intensity from 100 to 600 mol m-2 s-1 did not clearly affect the rate of phytosiderophore release. However, under Zn deficiency increases in light intensity markedly enhanced release of phytosiderophores in Zn-deficient Aroona, but not in Zn-inefficient Durati. When Fe-deficient barley cultivar Europe was grown first at 220 mol m-2 s-1 and then exposed to 600 mol m-2 s-1 for 24 and 48 h, the rate of release of phytosiderophores was enhanced about 4-fold and 7-fold, respectively. Transfer of Fe-deficient plants from 600 to 50 mol m-2 s-1 for 48 h reduced the rate of release of phytosiderophores by a factor of 7. The effect of light on phytosiderophore release was similar regardless of whether the rate of phytosiderophore release was expressed per plant or per unit dry weight of roots.The results demonstrate a particular role of light intensity in phytosiderophore release from roots under both Zn and Fe deficiency. It is suggested that in the studies concerning the role of phytosiderophore release in expression of Zn or Fe efficiency among and within cereals, a special attention should be given to the light conditions.     

Uptake of zinc by rye,bread wheat and durum wheat cultivars differing in zinc efficiency

Effect of zinc (Zn) nutritional status on uptake of inorganic ⁶⁵Zn was studied in rye (Secale cereale, cv. Aslim), three bread wheat (Triticum aestivum, cvs. Dagdas, Bezostaja, BDME-10) and durum wheat (Triticum durum, cv. Kunduru-1149) cultivars grown for 13 days in nutrient solution under controlled environmental conditions. The cultivars were selected based on their response to Zn deficiency and to Zn fertilization in calcareous soils under field conditions. When grown in Zn-deficient calcareous soil in the field, the rye cultivar had the highest, and the durum wheat the lowest Zn efficiency. Among the bread wheats, BDME-10 showed higher susceptibility to Zn deficiency and Bezostaja and Dagdas were less affected by Zn deficiency. Similarly to field conditions, in nutrient solution visual Zn deficiency symptoms (i.e. necrotic lesions on leaf blade) appeared to be more severe in Kunduru-1149 and BDME-10 and less severe in rye cultivar Aslim. Under Zn deficiency, shoot concentrations of Zn were similar between all cultivars. Cultivars with adequate Zn supply did not differ in uptake and root-to-shoot translocation rate of ⁶⁵Zn, but under Zn deficiency there were distinct differences; rye showed the highest rate of Zn uptake and the durum wheat the lowest. In the case of bread wheat cultivars, ⁶⁵Zn uptake rate was about the same and not related to their differential Zn efficiency. Under Zn deficiency, rye had the highest rate of root-to-shoot translocation of ⁶⁵Zn, while all bread and durum wheat cultivars were similar in their capacity to translocate ⁶⁵Zn from roots to shoots. When Zn²⁺ activity in uptake solution ranged between 117 p M and 34550 pM, Zn-efficient and Zn-inefficient bread wheat genotypes were again similar in uptake and root-to-shoot translocation rate of ⁶⁵Zn. The results indicate that high Zn efficiency of rye can be attributed to its greater Zn uptake capacity from soils. The inability of the durum wheat cultivar Kunduru-1149 to have a high Zn uptake capacity seems to be an important reason for its Zn inefficiency. Differential Zn efficiency between the bread wheat cultivars used in this study is not related to their capacity to take up inorganic Zn. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phytosiderophore release in relation to micronutrient metal deficiencies in barley

Phytosiderophore release occurs under both iron and zinc deficiencies in representative Poaceae and has been speculated to be a general adaptive response to enhance the acquisition of micronutrient metals. To test this hypothesis, phytosiderophore (PS) release rates from barley (Hordeum vulgare cv. CM72) subjected to deficiencies of Fe, Zn, Mn, and Cu were compared using chelator-buffered nutrient solutions. PS release rates were determined at two day intervals during onset and development of deficiency symptoms. Plant dry matter yields and nutrient concentrations, measured at three time points were used to construct growth curves for calculation of PS release per unit root mass and estimation of critical internal nutrient levels associated with PS release. In comparison to trace metal-sufficient control plants, dry matter production was markedly reduced in the Zn, Mn, and Cu deficiency treatments, with final relative yields of 49, 61, and 34%, respectively. Relative yields for Fe-deficient plants grown at three suboptimal Fe levels ranged from 95 to 33% of control, and provided a basis for comparison of PS release rates by Zn-, Mn-, and Cu-deficient plants at similar levels of growth inhibition. Under Fe deficiency, PS release increased with severity of the deficiency as measured by foliar Fe concentration, yield reduction, and chlorosis. Changes in PS release rates over time suggested a cyclical pattern that may be regulated by Fe concentration in the plant shoot. The highest rate of PS release (35 mol g^–1 root dw 2 h^–1) was measured after 10 days of growth at pFe 19, whereas control plants adapted for growth at pFe 17 released only 2 to 3 mol g^–1 root dw 2 h^–1. In a second experiment, maximum PS release rates for barley subjected to Zn, Mn, and Cu deficiencies were only 2.6, 2.5 and 1 mol g^–1 2 h^–1, respectively and were only slightly elevated over those of the control plants (ca. 1 mol g^–1 root dw 2 h^–1) grown at pFe 16.5. Moreover, enhanced PS release under Zn deficiency occurred much later, after the deficiency had already caused severely reduced growth. The results suggest that phytosiderophore release in this barley cultivar is a specific response to Fe deficiency and is not significantly induced in response to deficiencies of other trace metals.     

Phytosiderophore release by wheat genotypes differing in zinc deficiency tolerance grown with Zn-free nutrient solution as affected by salinity

There is limited information concerning the effect of salinity on phytosiderophores exudation from wheat roots. The aim of this hydroponic experiment was to investigate the effect of salinity on phytosiderophore release by roots of three bread wheat genotypes differing in Zn efficiency (Triticum aestivum L. cvs. Rushan, Kavir, and Cross) under Zn deficiency conditions. Wheat seedlings were transferred to Zn-free nutrient solutions and exposed to three salinity levels (0, 60, and 120 mM NaCl). The results indicated that Cross and Rushan genotypes exuded more phytosiderophore than did the Kavir genotype. Our findings suggest that the adaptive capacity of Zn-efficient ‘Cross’ and ‘Rushan’ wheat genotypes to Zn deficiency is due partly to the higher amounts of phytosiderophore release. Only 15 days of Zn deficiency stress was sufficient to distinguish between Zn-efficient (Rushan and Cross) and Zn-inefficient (Kavir) genotypes, with the former genotypes exuding more phytosiderophore than the latter. Higher phytosiderophore exudation under Zn deficiency conditions was accompanied by greater Fe transport from root to shoot. The maximum amount of phytosiderophore was exuded at the third week in ‘Cross’ and at the fourth week in ‘Kavir’ and ‘Rushan’. For all three wheat genotypes, salinity stress resulted in higher amounts of phytosiderophore exuded by the roots. In general, for ‘Kavir’, the largest amount of phytosiderophore was exuded from the roots at the highest salinity level (120 mM NaCl), while for ‘Cross’ and ‘Rushan’, no significant difference was found in phytosiderophore exudation between the 60 and 120 mM NaCl treatments. More investigation is needed to fully understand the physiology of elevated phytosiderophore release by Zn-deficient wheat plants under salinity conditions.     

Influence of varied zinc supply on re-translocation of cadmium (109Cd) and rubidium (86Rb) applied on mature leaf of durum wheat seedlings

Effect of varied zinc (Zn) supply (0, 0.1, 1, 5 M) on re-translocation of radio-labeled cadmium (¹⁰⁹Cd) and rubidium (⁸⁶Rb) from mature leaf to root and other parts of shoot was studied in 11-day-old durum wheat (Triticum durum cv. C-1252) plants grown in nutrient solution under controlled environmental conditions. Application of ¹⁰⁹Cd and ⁸⁶Rb was carried out by immersing the tips (3 cm) of mature leaf in radio-labeled solutions for 10 s at three different times over a 42 h period. Differences in Zn supply for 11 days did not affect plant growth nor did it cause visual leaf symptoms, such as necrosis and chlorosis, at either the lowest or the highest Zn supply. Only at the nil Zn supply (0 M), shoot and root dry weights tended to decrease and increase, respectively, causing a lower shoot/root dry weight ratio. Partitioning of more dry matter to roots rather than shoots, a typical phenomena for Zn-deficient plants in nutrient solution experiments, indicated existence of a mild Zn deficiency stress at the nil-Zn treatment. Irrespective of Zn supply, plants could, on average, retranslocate 3.8% and 38% of the total absorbed ¹⁰⁹Cd and ⁸⁶Rb from the treated leaf to roots and other parts of shoots within 42 h, respectively. At nil-Zn treatment, 2.8% of the total absorbed ¹⁰⁹Cd was re-translocated from the treated leaf, particularly into roots. The highest re-translocation of ¹⁰⁹Cd (6.5%) was found in plants supplied with 0.1 M Zn. Increases in Zn supply from 0.1 M reduced ¹⁰⁹Cd re-translocation from 6.5% to 4.3% at 1 M Zn and 1.3% at 5 M Zn. With the exception of the nil-Zn treatment, the proportion of re-translocated ¹⁰⁹Cd was greater in the remainder of the shoot than in the roots. Contrary to the ¹⁰⁹Cd results, re-translocation of ⁸⁶Rb was not (at 0, 0.1 and 1 M Zn), or only slightly (at 5 M), affected by changing Zn supply. The results indicate an inhibitory action of increased concentrations of Zn in shoot tissues on phloem-mediated Cd transport. This effect is discussed in relation to competitive inhibition of Cd loading into phloem sap by Zn.     

Species-specific N and P release rates in Daphnia

Bioavailable N and P release rates by juveniles and adults of three Daphnia taxa (D. hyalina, D. galeata and its interspecific hybrids D. hyalina × galeata) were measured to assess the effect of weight and interspecific differences on these rates in Daphnia. Immobilized Scenedesmus obliquus cells were used to estimate the release rates. The specific release rate of N varied between 5.19–5.71 g N mg C^-1 h^-1 for juveniles and 3.00–3.42 g N mg C^-1 h^-1 for adults. P excretion rate ranged between 1.93–2.37 g P mg C^-1 h^-1 for juveniles and 1.00–1.24 g P mg C^-1 h^-1 for adults. Our results show that the taxonomic affiliation of Daphnia individuals did not affect their N and P release rates.     

Differential response of rye,triticale, bread and durum wheats to zinc deficiency in calcareous soils

Field and greenhouse experiments were carried out to study the response of rye (Secale cereale L. cv. Aslim), triticale (× Triticosecale Wittmark. cv. Presto), two bread wheats (Triticum aestivum L, cvs. Bezostaja-1 and Atay-85) and two durum wheats (Triticum durum L. cvs. Kunduru-1149 and C-1252) to zinc (Zn) deficiency and Zn fertilization in severely Zn-deficient calcareus soils (DTPA-Zn=0.09 mg kg^-1 soil). The first visible symptom of Zn deficiency was a reduction in shoot elongation followed by the appearance of whitish-brown necrotic patches on the leaf blades. These symptoms were either absent or only slight in rye and triticale, but occurred more rapidly and severely in wheats, particularly in durum wheats. The same was true for the decrease in shoot dry matter production and grain yield. For example, in field experiments at the milk stage, decreases in shoot dry matter production due to Zn deficiency were absent in rye, and were on average 5% in triticale, 34% in bread wheats and 70%, in durum wheats. Zinc fertilization had no effect on grain yield in rye but enhanced grain yield of the other cereals. Zinc efficiency of cereals, expressed as the ratio of yield (shoot dry matter or grain) produced under Zn deficiency compared to Zn fertilization were, on average, 99% for rye, 74% for triticale, 59% for bread wheats and 25% for durum wheats.These distinct differences among and within the cereal species in susceptibility to Zn deficiency were closely related to the total amount (content) of Zn per shoot, but not with the Zn concentrations in shoot dry matter. For example, the most Zn-efficient rye and the Zn-inefficient durum wheat cultivar C-1252 did not differ in shoot Zn concentration under Zn deficiency, but the total amount of Zn per whole shoot was approximately 6-fold higher in rye than the durum wheat. When Zn was applied, rye and triticale accumulated markedly more Zn both per whole shoot and per unit shoot dry matter in comparison to wheats.The results demonstrate an exceptionally high Zn efficiency of rye and show that among the cereals studied Zn efficiency declines in the order rye>triticale>bread wheat>durum wheat. The differences in expression of Zn efficiency are possibly related to a greater capacity of efficient genotypes to acquire Zn from the soil compared to inefficient genotypes.     

Root exudation and Fe uptake and transport in wheat genotypes differing in tolerance to Zn deficiency

Tolerance to Zn deficiency in wheat germplasm may be inversely related to uptake and transport of Fe to shoots. The present study examined eight bread (Triticum aestivum) and two durum (T. turgidum L. conv. durum) wheat genotypes for their capacity to take up and transport Fe when grown under either Fe or Zn deficiency. Bread wheat genotypes Aroona, Excalibur and Stilleto showed tolerance to Zn and Fe deficiency, while durum wheat genotypes are clearly less tolerant to either deficiency. Roots of bread wheats tolerant to Zn deficiency exuded more phytosiderophores than sensitive bread and durum genotypes. Greater amounts of phytosideophores were exuded by roots grown under Fe than Zn deficiency. A relatively poor relationship existed between phytosiderophore exudation or the Fe uptake rate and relative shoot growth under Fe deficiency. At advanced stages of Zn deficiency, genotypes tolerant to Zn deficiency (Aroona and Stilleto) had a greater rate of Fe uptake than other genotypes. Zinc deficiency depressed the rate of Fe transport to shoots in all genotypes in early stages, while advanced Zn deficiency had the opposite effect. Compared with Zn-sufficient plants, 17-day-old Zn-deficient plants of genotypes tolerant to Zn deficiency had a lower rate of Fe transport to shoots, while genotypes sensitive to Zn deficiency (Durati, Yallaroi) had the Fe transport rate increased by Zn deficiency. A proportion of total amount of Fe taken up that was transported to shoots increased with duration of either Fe or Zn deficiency. It is concluded that greater tolerance to Zn deficiency among wheat genotypes is associated with the increased exudation of phytosiderophores, an increased Fe uptake rate and decreased transport of Fe to shoots. This revised version was published online in June 2006 with corrections to the Cover Date.     

Transient state characteristics of adaptation to changes in light conditions for the cyanobacterium Oscillatoria agardhii

Transitions in growth irradiance level from 92 to 7 Em^-2 s^-1 and vice versa caused changes in the pigment contents and photosynthesis of Oscillatoria agardhii. The changes in chlorophyll a and C-phycocyanin contents during the transition from high to low irradiance (HL) were reflected in photosynthetic parameters. In the LH transition light utilization efficiencies of the cells changed faster than pigment contents. This appeared to be related to the lowering of light utilization efficiencies of photosynthesis. As a possible explanation it was hypothesized that excess photosynthate production led to feed back inhibition of photosynthesis. Time-scales of changes in the maximal rate of O₂ evolution were discussed as changes in the number of reaction centers of photosystem II in relation to photosynthetic electron transport. Parameters that were subject to change during irradiance transitions obeyed first order kinetics, but hysteresis occurred when comparing HL with LH transients. Interpretation of first order kinetic analysis was discussed in terms of adaptive response vs changes in growth rate.Non-standard abbreviations Chla chlorophyll a - CPC C-phycocyanin - PS II photosystem II - PS I photosystem I - RC II reaction center of photosystem II - P photosynthetic O₂-evolution - I irradiance, Em^-2 s^-1 - light utilization efficiency of cells, mmol O₂·mg dry wt^-1·h^-1/Em^-2 s^-1 - light utilization efficiency of photosynthetic apparatus, mol O₂·mol Chla ^-1·h^-1/Em^-2 s^-1 - P_max maximal rate of O₂ evolution by cells, mol O₂·mg dry wt^-1·h^-1 - P_max maximal rate of O₂ evolution by photosynthetic apparatus, mol O₂·mol·Chla ^-1·h^-1 - LL low light, E m^-2 s^-1 - HL high light, E m^-2 s^-1 - LH low to high light transition - HL high to low light transition - k specific rate of adaptation, h^-1 - specific growth rate, h^-1 - Q pool size of cell constituent, mol·mg dry wt^-1 - q net synthesis rate of cell constituent, mol·mg dry wt^-1·h^-1     

Characterization of Zinc Uptake, Binding, and Translocation in Intact Seedlings of Bread and Durum Wheat Cultivars

Durum wheat (Triticum turgidum L. var durum) cultivars exhibit lower Zn efficiency than comparable bread wheat (Triticum aestivum L.) cultivars. To understand the physiological mechanism(s) that confers Zn efficiency, this study used ⁶⁵Zn to investigate ionic Zn²⁺ root uptake, binding, and translocation to shoots in seedlings of bread and durum wheat cultivars. Time-dependent Zn²⁺ accumulation during 90 min was greater in roots of the bread wheat cultivar. Zn²⁺ cell wall binding was not different in the two cultivars. In each cultivar, concentration-dependent Zn²⁺ influx was characterized by a smooth, saturating curve, suggesting a carrier-mediated uptake system. At very low solution Zn²⁺ activities, Zn²⁺ uptake rates were higher in the bread wheat cultivar. As a result, the Michaelis constant for Zn²⁺ uptake was lower in the bread wheat cultivar (2.3 μm) than in the durum wheat cultivar (3.9 μm). Low temperature decreased the rate of Zn²⁺ influx, suggesting that metabolism plays a role in Zn²⁺ uptake. Ca inhibited Zn²⁺ uptake equally in both cultivars. Translocation of Zn to shoots was greater in the bread wheat cultivar, reflecting the higher root uptake rates. The study suggests that lower root Zn²⁺ uptake rates may contribute to reduced Zn efficiency in durum wheat varieties under Zn-limiting conditions.Soils that contain insufficient levels of the essential plant micronutrient Zn are common throughout the world. As a result, Zn deficiency is a widespread problem in crop plants, especially cereals (Graham et al., 1992). The importance of plant foods as sources of Zn, particularly in the marginal diets of developing countries, is well established (Welch, 1993). The development of crop plants that are efficient Zn accumulators is therefore a potentially important endeavor. In addition to its effects on nutrition, Zn deficiency in crops is relevant to other areas of human health. Another consequence of Zn-deficient soils is the tendency for plants grown in such soils to accumulate heavy metals. For example, in the Great Plains region of North America, where soil Zn levels are low and naturally occurring Cd is present, durum wheat (Triticum turgidum L. var durum) grains accumulate Cd to relatively high concentrations (Wolnik et al., 1983). The presence of Cd in food represents a potential human health hazard and, in response, international trade standards have been proposed to limit the levels of Cd in exported grain (Codex Alimentarius Commission, 1993). Thus, there is a need to understand the physiological processes that control acquisition of Zn from soil solution by roots and mobilization of Zn within plants.It has been demonstrated in recent years that crop plants vary in their ability to take up Zn, particularly when its availability to roots is limited. Zn efficiency, defined as the ability of a plant to grow and yield well in Zn-deficient soils, varies among wheat cultivars (Graham and Rengel, 1993). In field trials, durum wheat cultivars have been shown to be consistently less Zn efficient than bread wheat (Triticum aestivum L.) cultivars (Graham et al., 1992). Similarly, durum wheat varieties were reported to be less Zn efficient than bread wheat varieties when grown in chelate-buffered hydroponic nutrient culture (Rengel and Graham, 1995a).The physiological mechanism(s) that confers Zn efficiency has not been identified. Processes that could influence the ability of a plant to tolerate limited amounts of available Zn include higher root uptake, more efficient utilization of Zn, and enhanced Zn translocation within the plant. Cakmak et al. (1994) showed that a Zn-inefficient durum wheat cultivar exhibited Zn-deficiency symptoms earlier and more intensely than a Zn-efficient bread wheat cultivar even though the Zn tissue concentrations were similar in both lines, suggesting differential utilization of Zn in the two cultivars. Rates of Zn translocation to shoots were shown to vary among sorghum cultivars, although correlations with Zn efficiency were not established (Ramani and Kannan, 1985). Root uptake kinetics have been reported to vary between rice cultivars having different Zn requirements, with high-Zn-requiring cultivars exhibiting consistently higher root uptake rates (Bowen, 1986). In contrast, a correlation between Zn efficiency and rates of root Zn uptake in bread and durum wheat cultivars could not be demonstrated (Rengel and Graham, 1995b).In grasses Zn influx into the root symplasm has been hypothesized to occur as the free Zn²⁺ ion (Halvorson and Lindsay, 1977), as well as in the form of Zn complexes with nonprotein amino acids known as phytosiderophores (Tagaki et al., 1984) or phytometallophores (Welch, 1993). Concentration-dependent uptake of free Zn²⁺ ions has been shown to be saturable in several species, including maize (Mullins and Sommers, 1986), barley (Veltrup, 1978), and wheat (Chaudhry and Loneragan, 1972), suggesting that ionic uptake in grasses occurs via a carrier-mediated system. However, several of these studies have been criticized on the basis that excessively high (and physiologically unrealistic) Zn²⁺ concentrations were used (Kochian, 1993).This study was undertaken to examine unidirectional Zn²⁺ influx and translocation to shoots in Zn-efficient bread wheat lines and Zn-inefficient durum wheat lines. Experiments were performed in the absence of added phytometallophores and results are presumed to represent influx of ionic Zn²⁺. Zn activities in the nanomolar range were used to more closely mimic free Zn²⁺ levels occurring naturally in soil solution. The results presented here indicate that a Zn-efficient bread wheat cultivar maintained higher rates of Zn uptake than a Zn-inefficient durum wheat cultivar, particularly at low (and physiologically relevant) solution Zn²⁺ activities.     

Transfer of the 1BL/1RS wheat-rye-translocation from hexaploid bread wheat to tetraploid durum wheat

Summary The present study describes a cytological stable alien chromosome translocation in tetraploid durum wheat. By crossing the hexaploid 1BL/1RS wheat-rye translocation line Veery to the tetraploid durum wheat cultivar Cando it was possible to select a 28 chromosomic strain homozygous for the 1BL/1RS translocation. The disease resistance potential of the short arm of rye chromosome 1R, which has been widely introduced in many hexaploid bread wheat cultivars could be now also used for the improvement of durum wheat.     

pH inhibition of yeast ethanol fermentation in continuous culture

Summary In a low dilution rate study an unexpected pH-related inhibition of yeast fermentation was found. A higher volumetric rate of ethanol production occurred at lower pH values (2.8 to 3.2), suggesting a low optimum pH.Notation Ki product inhibition constant, L/g - Ks substrate saturation constant, g/L - P product (ethanol) concentration, g/L - S substrate (glucose) concentration, g/L - specific growth rate, h^–1 - ₀ maximum specific growth rate, h^–1     

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.     

Genetics of yellow berry in wheat (Triticum aestivum)

Summary The inheritance of yellow berry, a grain disorder in durum and bread wheats, was studied in six intervarietal crosses in bread wheat. The trait was found to be controlled by either two or three dominant genes. Monosomic analysis using Chinese Spring monosomic series showed the presence of two major dominant genes on chromosomes 1A and 7A, and four modifiers on 4A, 4B, 6A and 6D, which influence the expression of yellow berry in bread wheat.     

Seedling responses of three Australian tree species to toxic concentrations of zinc in solution culture

A frequently desired outcome when rehabilitating Zn toxic sites in Australia is to establish a self-sustaining native ecosystem. Hence, it is important to understand the tolerance of Australian native plants to high concentrations of Zn. Very little is known about the responses of Australian native plants, and trees in particular, to toxic concentrations of Zn. Acacia holosericea, Eucalyptus camaldulensis and Melaleuca leucadendra plants were grown in dilute solution culture for 10 weeks. The seedlings (42 days old) were exposed to six Zn treatments viz., 0.5, 5, 10, 25, 50 and 100 M. The order of tolerance to toxic concentrations of Zn was E. camaldulensis> A. holosericea> M. leucadendra, the critical external concentrations being approximately 20, 12 and 1.5 M, respectively. Tissue Zn concentrations increased as solution Zn increased for all species. Root tissue concentrations were higher than shoot tissue concentrations at all solution Zn concentrations. The critical tissue Zn concentrations were approximately 85 and 110 g g^–1 DM for M. leucadendra, 115 and 155 g g^–1 DM for A. holosericea and 415 and 370 g g^–1 DM for E. camaldulensis for the youngest fully expanded leaf and total shoots, respectively. The results from this paper provide the first comprehensive combination of growth responses, critical external concentrations, critical tissue concentrations and plant toxicity symptoms for three important Australian genera, viz., Eucalyptus, Acacia and Melaleuca, for use in the rehabilitation of potentially Zn toxic sites.     

Feeding in the rotifer Brachionus calyciflorus

Summary The laboratory feeding behavior of Brachionus calyciflorus varies depending upon the type of food cell available in suspension. When feeding on the yeast Rhodotorula glutinis, rotifers show a continuous increase in ingestion with increased cell density between 0.01 and 1000 g dry weight ml^-1. Effective clearance rates drop from ca. 50 l animal^-1 h^-1 to less than 0.5 l animal^-1 h^-1 over this food density range. When feeding on Englena gracilis, B. calyciflorus ingestion rates are constant between 1.0 and 100 g ml^-1 of available food, averaging close to 25 ng animal^-1 h^-1. The decrease in clearance rate is more striking than with R. glutinis, dropping from 45 l animal^-1 h^-1 at 0.1 g ml^-1 to 0.13 l animal^-1 h^-1 at 100 g ml^-1. Differences between the patterns obtained with the two food types indicate fundamental dissimilarities in the feeding behavior of this rotifer species when presented with these different foods.     

Product inhibition during the feeding phasein fed-batch ethanol fermentation of sugar-cane blackstrap molasses

Summary The following equations represent the influence of the ethanol concentration (E) on the specific growth rate of the yeast cells () and on the specific production rate of ethanol () during the reactor filling phase in fed-batch fermentation of sugar-cane blackstrap molasses: = ₀ - k · E and v = v ₀ · K/(K +E) Nomenclature E ethanol concentration in the aqueous phase of the fermenting medium (g.L^–1) - E_m value of E when = 0 or = 0 (g.L^–1) - F medium feeding rate (L.h^–1) - k empirical constant (L.g^–1.h^–1) - K empirical constant (g.L^–1) - M_as mass of TRS added to the, reactor (g) - M_cs mass of consumed TRS (g) - M_e mass of ethanol in the aqueous phase of the fermenting medium (g) - M_s mass of TRS in the aqueous phase of the fermenting medium (g) - M_x mass of yeast cells (dry matter) in the fermenting medium (g) - r correlation coefficient - S TRS concentration in the aqueous phase of the fermenting medium (g.L^–1) - S_m TRS concentration of the feeding medium (g.L^–1) - t time (h) - T temperature (° C) - TRS total reducing sugars calculated as glucose - V volume of the fermenting medium (L) - V₀ volume of the inoculum (L) - X yeast cells concentration (dry matter) in the fermenting medium (g.L^–1) - filling-up time (h) - specific growth rate of the yeast cells (h^–1) - ₀ value of when E=0 - specific production rate of ethanol (h^–1) - ₀ value of when E=0 - density of the yeast cells (g.L^–1) - dry matter content of the yeast cells     

Effects of Cd and Zn on the development of annual xylem rings of young Norway spruce (Picea abies) plants

Three-year-old spruce (Picea abies) saplings were planted and cultivated for 2 years in pots with 3 1 substrate, consisting of a homogenized mixture of sand, peat and forest soil with a high organic content (volume ratio 11.52). This substrate was amended with 10–180 mol Cd [kg soil dry weight (DW)]^–1, 50–7500 mol Zn (kg soil DW)^–1 (determined with 1 M ammonium acetate extracts) or combinations of both elements. Annual xylem growth rings in stems of plants treated with 50 mol Cd (kg soil DW)^–1 or 7500 mol Zn (kg soil DW)^–1 were significantly narrower than in control plants. Growth reductions were more pronounced in the second year of the experiment. The contents of Cd and Zn in stem wood and needles were positively correlated with the substrate concentrations. The Mg contents of the spruce needles were inversely correlated with soil concentrations of Cd and Zn. Root development was impeded at moderate concentrations of Cd (50 mol kg^–1) or Zn (1000 mol kg^–1) in the substrate. The adverse effects of potentially toxic trace elements, like Cd or Zn, on xylem growth of spruce plants are discussed with regard to possible growth reductions in forest trees under field conditions.     

Effect of dilution rate on the release of pertussis toxin and lipopolysaccharide ofBordetella pertussis

Summary The kinetics ofBordetella pertussis growth was studied in a glutamate-limited continuous culture. Growth kinetics corresponded to Monod's model. The saturation constant and maximum specific growth rate were estimated as well as the energetic parameters, theoretical yield of cells and maintenance coefficient. Release of pertussis toxin (PT) and lipopolysaccharide (LPS) were growth-associated. In addition, they showed a linear relationship between them. Growth rate affected neither outer membrane proteins nor the cell-bound LPS pattern.Nomenclature X cell concentration (g L^–1) - specific growth rate (h^–1) - _m maximum specific growth rate (h^–1) - D dilution rate (h^–1) - S concentration of growth rate-limiting nutrient (glutamate) (mmol L^–1 or g L^–1) - Ks substrate saturation constant (mol L^–1) - m_s maintenance coefficient (g g^–1 h^–1) - Y_x/s theoretical yield of cells from glutamate (g g^–1) - Y_x/s yield of cells from glutamate (g g^–1) - Y_PT/s yield of soluble PT from glutamate (mg g^–1) - Y_KDO/s yield of cell-free KDO from glutamate (g g^–1) - Y_PT/x specific yield of soluble PT (mg g^–1) - Y_KDO/x specific yield of cell-free KDO (g g^–1) - q_PT specific soluble PT production rate (mg g^–1 h^–1) - q_KDO specific cell-free KDO production rate (g g^–1 h^–1)