Functional analysis of transgenic rice (Oryza sativa L.) transformed with an Arabidopsis thaliana ferric reductase (AtFR02)

Iron deficient soils limit crop production on 25-30% of the world's arable land. Both grasses (Strategy 11) and dicotyledonous crops (Strategy 1) are susceptible to iron deficiency, but each respond to iron stress by different mechanisms. In order to acquire iron from the soil, Strategy I plants utilize an iron reduction and Fe²⁺ transporter system at the root level, whereas Strategy 11 plants use a phytosiderophore-based system. Unfortunately, in some grasses such as rice, the production of phytosiderophores is low, and thus their ability to survive in iron-deficient conditions is limited. To determine whether a Strategy I root reductase can function in a Strategy 11 plant, and enhance its iron acquisition, we inserted the FRO2 gene from Arabidopsis thaliena (AtFR02) into rice (Oryza sativa). Root reductase activity was determined and was found to be low in both transgenic and control plants grown at different iron concentrations. The low activity levels were attributed to the release of soluble reductants in the assay and not to membrane-localized root reductase activity. RT-PCR analysis of rice roots and shoots of plants grown hydroponically at different iron concentrations revealed no expression of the transgene. In this paper, we discuss the lack of functionality of the AtFRO2 gene in rice, and we perform a comparative study of the 0.6 kb promoter region by PlantCARE and PLACE analysis.     

Iron-deficiency response and expression of genes related to iron homeostasis in poplars

Iron (Fe) deficiency is a serious agricultural problem, especially in calcareous soils, which are distributed worldwide. Poplar trees are an important biomass plant, and overcoming Fe deficiency in poplars will increase biomass productivity worldwide. The poplar Fe-deficiency response and the genes involved in poplar Fe homeostasis remain largely unknown. To identify these genes and processes, we cultivated poplar plants under Fe-deficient conditions, both in calcareous soil and hydroponically, and analyzed their growth rates, leaf Soil and Plant Analyzer Development (SPAD) values, and metal concentrations. The data clearly showed that poplars have notable growth defects in both calcareous soil and a Fe-deficient hydroponic culture. They exhibited serious chlorosis of young leaves after 3 weeks of Fe-deficient hydroponic culture. The Fe concentrations in old leaves with high SPAD values were markedly lower in Fe-deficient poplars, suggesting that poplars may have good translocation capability from old to new leaves. The Zn concentration in new leaves increased in Fe-deficient poplars. The pH of the hydroponic solution decreased in the Fe-deficient culture compared to the Fe-sufficient culture. This finding shows that poplars may be able to adjust the pH of a culture solution to better take up Fe. We also analyzed the expression of Fe homeostasis-related genes in the roots and leaves of Fe-sufficient and Fe-deficient poplars. Our results demonstrate that PtIRT1, PtNAS2, PtFRO2, PtFRO5, and PtFIT were induced in Fe-deficient roots. PtYSL2 and PtNAS4 were induced in Fe-deficient leaves. PtYSL3 was induced in both Fe-deficient leaves and roots. These genes may be involved in the Fe uptake and/or translocation mechanisms in poplars under Fe-deficient conditions. Our results will increase a better understanding of the Fe-deficiency response of poplars and hence improve the breeding of Fe-deficiency-tolerant poplars for improved biomass production, the greening of high pH soils, and combatting global warming.     

Iron deficiency enhances cadmium uptake and translocation mediated by the Fe2+ transporters OsIRT1 and OsIRT2 in rice

Abstract

Cadmium (Cd) accumulation in rice grains is enhanced if ponded water is released from paddy fields during the reproductive stage (intermittent irrigation). The release of ponded water creates aerobic soil conditions under which Cd becomes soluble and iron (Fe) solubility decreases. We hypothesized that Fe shortage in rice induces Fe uptake and translocation and that Cd is also taken up and translocated throughout this process. Hydroponically cultured Fe-deficient rice absorbed more Cd than did Fe-sufficient rice, and the presence of Fe enhanced the translocation of Cd to the shoots. Yeast mutants expressing OsIRT1 and OsIRT2, which encode the rice Fe²⁺ transporter, became more sensitive to Cd, suggesting that Cd was absorbed by OsIRT1 and OsIRT2. We discuss the possibility that Cd accumulation in rice grains during the reproductive stage is mediated by the Fe transport system.     

Localized root growth in soil induced by controlled‐release urea granule and barley nitrogen uptake

Controlled‐release urea is a fertilizer which meters out urea over a long period of time. It can provide a favorable nitrogen (N) concentration for root growth, especially at the early stage of plant development. The objective of this study was to determine the interactions of urea or controlled‐release urea granules with barley roots and the resultant N uptake by plants. Two experiments (Experiment I and Experiment II) with treatments of Nil, non‐coated urea, Coated I and Coated II (Coated I and Coated II are controlled‐release urea products) were conducted in a greenhouse at 23±5°C. In both experiments, one barley (Hordeum vulgare L. cv. Duke) seed and one granule of urea or controlled‐release urea were placed in a pot (5.2‐cm height and 8‐cm diameter) containing soil low in mineral N. In Experiment I, shoot and soil samples were taken at 14, 28, and 46 days after seeding. Roots and fertilizer interaction were visually examined and photographed. In Experiment II, root samples both around the fertilizer granule and away from the granule were taken only at 28 days after seeding. In both experiments, dry matter mass and total N content of shoot and root, and mineral N in soil were determined. In Experiment I, at the 28‐day sampling roots proliferated around the controlled‐release urea granule but not around the urea granule. Shoot N uptake since the 28 days was higher with controlled‐release urea than with urea because of the root proliferation. In Experiment II, root dry mass and N content around the granule was higher with controlled‐release urea than with urea. In the controlled‐release urea treatments, root mass and N content away from the granule were also increased in comparison to the Nil. This shows a stimulus relationship between the two portions of the roots in the same plant, i.e., the roots being accessed to the N source increased growth of the other roots with no access to the source. Because only a small portion of roots was involved in N uptake in the controlled‐release urea treatments, the intensity of N uptake per unit of root mass was much higher with controlled‐release urea as compared to urea. In conclusion, root growth was enhanced around controlled‐release urea granule, and that portion of roots around the fertilizer granule played a major role in absorbing N. In addition, a stimulus relationship existed between roots grown around the granule and those grown away from the granule.     

Effects of Bicarbonate Content of Irrigation Water on Nutritional Disorders of Some Apple Varieties*

Effects of varying concentrations of bicarbonate in the irrigation water on seedlings of ‘Red Delicious,’ ‘Golden Delicious,’ and ‘Golab-e-Kohanz’ apple cultivars, grown in a greenhouse, were studied. To conduct this experiment, ammonium bicarbonate was used in order to obtain bicarbonate concentrations at 5, 10, 15, and 30 meq/L, and sulfuric acid was used to obtain a 0 level of bicarbonate in water. The electrical conductivity (EC) of the leachate water was nearly the same for 0, 5, and 10 meq/L bicarbonate, but doubled with the increase from 10 to 30 meq/L. Also, the bicarbonate concentration in the leachate increased with increasing levels of irrigation water bicarbonate, even though it was much lower in the leachates. Different bicarbonate levels in the irrigation water significantly reduced chlorophyll development. The difference was significant only between 30 mg/L and other levels after 40 d, but after 120 d (except for 0 and 5 meq/L) treatments at all other levels showed reduced chlorophyll intensities. There were also significant differences in chlorophyll intensities between different apple varieties before and up to 40 d of bicarbonate treatment, with ‘Golden Delicious’ having the most chlorophyll among the three varieties. The different intensities, however, were not significant after 80 and 120 d of bicarbonate treatments. After 120 d, the 0, 5, 10, 15, and 30 meq/L of bicarbonate had reduced the chlorophyll intensities by 4%, 6.5%, 18.2%, 35.6%, and 59.4%, respectively. Increasing levels of bicarbonate increased the leaf concentrations of nitrogen (N), potassium (K), and phosphorus (P), but lowered the concentrations of iron (Fe), magnesium (Mg), and manganese (Mn) and did not affect calcium (Ca), copper (Cu), or zinc (Zn) levels. Considering the equilibrium level of 3.5–4 mmole bicarbonate per liter of soil solution in calcareous soils brought about by CO₂ pressures and calcium carbonate (CaCO₃) minerals in the solid phase, it would not seem necessary to neutralize the irrigation water bicarbonates for concentrations below 5 meq/L. Instead, improvements in root development by improved soil aeration and prevention of excessive irrigation is probably beneficial. However, when the concentration of bicarbonate exceeds 5 meq/L in irrigation water, it is probably necessary to neutralize the bicarbonates for long-term irrigation purposes.     

Foliar Iron Fertilization: A Critical Review

Application of foliar iron (Fe) sprays is a common means of correcting Fe deficiency of agricultural crops. However, variable plant responses to iron sprays, ranging from no effect to defoliation, have often been described in the Fe-fertilization literature. Knowledge is still limited concerning the mechanisms of penetration of a leaf-applied, Fe-containing solution and the role of Fe in the leaf. The complex and multi-disciplinary character of the factors determining the effects of Fe sprays hinder the development of suitable foliar fertilization strategies, applicable under variable local conditions and for different plant types. This review describes some key factors involved on the process of penetration of a leaf-applied, Fe-containing solution before briefly analyzing the available foliar Fe-fertilization literature. Iron chemistry, leaf penetration, and plant-nutrition principles will be merged with the aim of clarifying the constraints, opportunities, and future perspectives of foliar Fe sprays to cure plant Fe deficiency.     

DIAGNOSIS AND RECOMMENDATION INTEGRATED SYSTEM: A TOOL FOR DETECTING NUTRIENT DEFICIENCIES IN YAM

The objective of the study carried out in the Upper Oueme Catchment in Benin (West Africa) was to assess the nutrient status in yam (Dioscorea rotundata) through the Diagnostic and Recommendation Integrated System (DRIS), to compare yield, foliar nutrient concentrations and the variance of nutrients of low-and high-yielding groups. Field experiments were carried out in 2001 and 2002 using a randomized complete block design with four treatments, 2001: n = 80, 2002: n = 109) at three sites: Beterou, Dogue, and Wewe. Nitrogen (N), followed by potassium (K), phosphorus (P), and magnesium (Mg) were identified as the most limiting nutrients in 2001 whereas sulfur (S) followed by N was identified as most limiting ones in 2002. Imbalanced nutrition was observed in both the years but was higher in 2001 compared in 2002. They may be utilized as a basis for calibrating the fertilization program of yam.     

Iron absorption,localization, and biomineralization of Cynodon dactylon,a perennial grass from the Río Tinto basin (SW Iberian Peninsula)

Cynodon dactylon (L.) Pers. is a perennial rhizomatous grass (Poaceae), grown for cattle nutrition on the riverbanks of Río Tinto (Southwest Iberian Peninsula, Spain), a highly acidic area with high concentrations of iron (Fe) and other metals. This study focuses on the absorption, distribution, and accumulation of Fe in the root, rhizome, and leaves of C. dactylon under controlled conditions. Plants collected from Río Tinto were grown in a Hoagland solution containing 500 mg kg^–1 of ferrous Fe. Samples were collected up to 2 months after exposure and analyzed for total Fe concentration using inductively coupled plasma–mass spectrometry (ICP‐MS) and for Fe distribution and bioformations by scanning electron microscopy (SEM) with an energy‐dispersive x‐ray analyzer (EDX). The results show high concentrations of Fe in all plant organs, with fast Fe translocation from roots to leaves. Iron bioformations composed mainly of Fe, S, and K were detected in all plant organs and were especially apparent in roots and leaves. These results differ from those reported for another species of Poaceae, Imperata cylindrica, which grows under the same environmental conditions, suggesting the existence of different resistance strategies between species of the same family.     

花铃期缺水对棉花产量和品质的影响

1986～1989年在大田和盆栽条件下研究了花铃期缺水对棉花产量和品质的影响。结果表明,整个花铃期缺水对棉株生长发育、生理代谢、干物质积累和分配以及产量和品质等均有不良影响。但盛花期缺水对其影响最大;初花期轻度缺水,能适当控制营养生长,减少用水量,对籽棉产量无不利影响,但此期严重缺水时会明显抑制营养生长,造成减产。干旱引起减产主要是由于单株铃数的减少,而平均铃重和衣分率对其影响较小,干旱条件下衣分率反而有提高的趋势。干旱对种子发育的影响大于对纤维发育的影响。对其它品质指标的影响较小。     

QTLs for phosphorus deficiency tolerance detected in upland NERICA varieties

Phosphorous (P) deficiency is a major yield limiting factor in rice (Oryza sativa L.) production. The interspecific New Rice for Africa (NERICA) varieties combine general stress tolerance from African cultivated rice (Oryza glaberrima Steud) with characteristics associated with high yield from O. sativa. However, little is known about their ability to tolerate P deficiency. Here, we examined the variation for tolerance to P deficiency among the 18 upland NERICAs and their parents in multi‐year field experiments. The good performance under P deficiency of the O. glaberrima parent CG 14 and some NERICAs suggested that these tolerant NERICAs contain loci associated with P deficiency tolerance inherited from CG 14. Additionally, four QTL clusters for P deficiency tolerance were detected on chromosomes 4, 6 and 11 using F₃ lines derived from the cross between the P deficiency tolerant variety NERICA10 and a Japonica‐type sensitive variety ‘Hitomebore’. These QTLs represent the first step in identifying stress tolerance genes from O. glaberrima that could subsequently be used to enhance P deficiency tolerance in O. sativa.