Reductase Activity In Roots Research Articles

Cadmium tolerance is associated with the root-driven coordination of cadmium sequestration, iron regulation, and ROS scavenging in rice

Excess cadmium (Cd) is a serious threat to agriculture and the environment. High Cd availability showed no significant decline in growth, chlorophyll synthesis, soluble protein, cell and membrane stability in Sonarbangla (Cd-tolerant), while these were severely affected in BRRI 72 (Cd-sensitive). Atomic absorption spectroscopy analysis demonstrated a huge increment of Cd and Fe in root and shoot of BRRI 72; however, Sonarbangla only exhibited a significant increase of Cd in roots. It suggests that excess Cd in Sonarbangla possibly retained in roots through vacuolar sequestration without interfering cell functions. This was further confirmed by the increased accumulation of cysteine, glutathione, and phytochelatin along with OsPCS1 and OsHMA3 upregulation, possibly facilitated by nitric oxide in roots of Sonarbangla. Further, Fe chelate reductase activity in conjunction with the genes (OsFRO1, OsNRAMP1, OsIRT1, and OsYSL15) associated with Fe availability significantly upregulated in BRRI 72 but not in Sonarbangla in response to Cd. It advises that Fe acquisition and transport were tightly regulated in Cd-tolerant Sonarbangla. Furthermore, elevated CAT, APX, GR, NO in root along with shoot sugar helps rice plants to withstand Cd-induced oxidative damage. Finally, reciprocal grafting combining Sonarbangla rootstock with either BRRI 72 or Sonarbangla scion showed Sonarbangla type tolerance along with no changes of H2O2 and Fe reductase activity in roots under high Cd. It indicates that the signal inducing the responses to adjust Cd stress is originated in the root system. These messages deliver essential background for further breeding program to produce Cd-free rice.

Biological Effects of Seed Irradiation by Synchrotron X Ray Beam in Young Bean Seedlings

Irradiated seeds of Phaseolus vulgaris cv. Rajmah using Synchrotron X Ray Beam (BL-07) in RRCAT, Indore at doses of 1, 10 and 20 Gy were used to raise the seedling and the effects on growth and biochemical constituents in 4 - 8 days, old seedlings were analyzed. The seed irradiation effect on seedling development up to about 4 - 5 days, % germination, seedling length and seedling vigor are significantly decreased at 10 and 20 Gy doses with strong -ve correlation. Other parameters, like relative water content, electrical conductivity and acid phosphatase activity are also decreased. Decrease in various biochemical constituents, like, protein and proline has shown significant reduction at 10 and 20 Gy and phenol at 1 - 20 Gy. However, peroxidase activity is increased at 1 and 10 Gy. Amongst the antioxidant enzymes, only superoxide dismutase activity has shown significant increase at 10 and 20 Gy. For seed irradiation (1 and 10 Gy) effect on seedling development up to 8 days involving transfer to hydroponic culture after 4 days, in shoot tissue, decrease in nitrate reductase activity and pigment content is observed, while nitrate reductase activity in root tissue is increased. The results demonstrate adverse effects on growth as well as biochemical constituents along with increased antioxidant effect in bean seedlings with irradiation of seeds at high dose of synchrotron X radiations. Also the nitrate assimilation and photosynthetic activity are reduced in shoot tissue with seed irradiation, however, increased nitrate reductase activity in roots suggests the involvement of NO signaling.

The ethylene response factor AtERF4 negatively regulates the iron deficiency response in Arabidopsis thaliana.

Iron (Fe) deficiency is one of many conditions that can seriously damage crops. Low levels of photosynthesis can lead to the degradation of chlorophyll content and impaired respiration in affected plants, which together cause poor growth and reduce quality. Although ethylene plays an important role in responses to Fe deficiency, a limited number of studies have been carried out on ethylene response factor (ERFs) as components of plant regulation mechanisms. Thus, this study aimed to investigate the role of AtERF4 in plant responses to Fe deficiency. Results collected when Arabidopsis thaliana was grown under Fe deficient conditions as well as in the presence of 1-aminocyclopropane-1-carboxylic acid (ACC) revealed that leaf chlorosis did not occur over short timescales and that chloroplast structural integrity was retained. At the same time, expression of the chlorophyll degradation-related genes AtPAO and AtCLH1 was inhibited and net H+ root flux was amplified. Our results show that chlorophyll content was enhanced in the mutant erf4, while expression of the chlorophyll degradation gene AtCLH1 was reduced. Ferric reductase activity in roots was also significantly higher in the mutant than in wild type plants, while erf4 caused high levels of expression of the genes AtIRT1 and AtHA2 under Fe deficient conditions. We also utilized yeast one-hybrid technology in this study to determine that AtERF4 binds directly to the AtCLH1 and AtITR1 promoter. Observations show that transient over-expression of AtERF4 resulted in rapid chlorophyll degradation in the leaves of Nicotiana tabacum and the up-regulation of gene AtCLH1 expression. In summary, AtERF4 plays an important role as a negative regulator of Fe deficiency responses, we hypothesize that AtERF4 may exert a balancing effect on plants subject to nutrition stress.

Ferric-chelate reductase activity is a limiting factor in iron uptake in spinach and kale roots

Iron (Fe) is essential for many vital processes in plants, including chlorophyll biosynthesis, DNA synthesis, nitrogen reduction, and photosynthetic electron transfer. However, free Fe ions also participate in the Fenton reaction, which generates reactive oxygen species that induce oxidative stress, leading to lipid peroxidation, protein oxidation, and DNA mutation. Accordingly, plants have developed strategies to prevent roots from absorbing excess Fe. Here, we investigated Fe homeostasis in hydroponically grown spinach and kale under various Fe concentrations (5-800 µM), as well as the resulting changes in bioactive compound levels. Spinach and kale Fe contents did not increase under Fe concentrations in the nutrient solution of up to 200 µM. When spinach plants (grown in nutrient solution containing 2 µM Fe-EDTA) were transferred to 50 µM Fe-EDTA, ferric-chelate reductase activity in roots rapidly decreased within 24 hours. In kale, ferric-chelate reductase activity also significantly decreased with increasing Fe-EDTA concentration. As Fe did not accumulate in spinach plants, no significant differences in plant growth were observed. However, in kale, root growth was slightly suppressed by high Fe (100-200 µM) levels in the rhizosphere. Comparisons to other studies suggest that variations in phenolic and flavonoid contents are dependent on plant species, but overall, Fe treatment did not result in a significant increase in these compounds in spinach or kale. Our results suggest that in spinach and kale roots, the regulation of Fe contents by ferric-chelate reductase is responsible for maintaining Fe homeostasis.

Silicon ameliorates chromium toxicity through phytochelatin-mediated vacuolar sequestration in the roots of Oryza sativa (L.)

ABSTRACTHigh chromium (Cr) in rice causes reduced yield and health hazards. This work investigates how Si alleviates Cr toxicity in rice. Addition of Si under Cr stress restored the growth parameters, total protein content, and membrane stability along with reduced Cr content in shoots, confirming that Si plays critical roles in Cr detoxification in rice. However, Si supplementation under Cr stress caused no significant changes in root Cr content but decreased shoot Cr concentrations compared with Cr-stressed plants, indicating that alleviation of Cr toxicity might be associated with Cr sequestration in roots. Further, concentration of Fe and expression of Fe transporter (OsIRT1) showed no significant changes due to Si supplementation under Cr stress, implying that Fe regulation is not involved with Si-mediated mitigation of Cr toxicity in rice. Further, phytochelatin accumulation and OsPCS1 (phytochelatin synthase) transcripts strongly induced due to the dual treatment of Si and Cr compared with Cr-stressed plants, suggesting that phytochelatin might bind to Cr, which leads to vacuolar sequestration in roots. Furthermore, increased glutathione reductase activity in roots implies that active involvement of ROS scavenging partially ameliorates Cr toxicity in rice plants. The study illustrates first evidences on the effect of Si alleviating Cr toxicity in rice plants.

Cross-Regulation between N Metabolism and Nitric Oxide (NO) Signaling during Plant Immunity.

Plants are sessile organisms that have evolved a complex immune system which helps them cope with pathogen attacks. However, the capacity of a plant to mobilize different defense responses is strongly affected by its physiological status. Nitrogen (N) is a major nutrient that can play an important role in plant immunity by increasing or decreasing plant resistance to pathogens. Although no general rule can be drawn about the effect of N availability and quality on the fate of plant/pathogen interactions, plants’ capacity to acquire, assimilate, allocate N, and maintain amino acid homeostasis appears to partly mediate the effects of N on plant defense. Nitric oxide (NO), one of the products of N metabolism, plays an important role in plant immunity signaling. NO is generated in part through Nitrate Reductase (NR), a key enzyme involved in nitrate assimilation, and its production depends on levels of nitrate/nitrite, NR substrate/product, as well as on L-arginine and polyamine levels. Cross-regulation between NO signaling and N supply/metabolism has been evidenced. NO production can be affected by N supply, and conversely NO appears to regulate nitrate transport and assimilation. Based on this knowledge, we hypothesized that N availability partly controls plant resistance to pathogens by controlling NO homeostasis. Using the Medicago truncatula/Aphanomyces euteiches pathosystem, we showed that NO homeostasis is important for resistance to this oomycete and that N availability impacts NO homeostasis by affecting S-nitrosothiol (SNO) levels and S-nitrosoglutathione reductase activity in roots. These results could therefore explain the increased resistance we noted in N-deprived as compared to N-replete M. truncatula seedlings. They open onto new perspectives for the studies of N/plant defense interactions.

The difference in responses to nitrogen deprivation and re-supply at seedling stage between two barley genotypes differing nitrogen use efficiency

Understanding how crops respond to limited nitrogen supply is essential to develop new ways of manipulating genes for breeding new crop cultivars or lines with high nitrogen use efficiency (NUE). However, little is known about the differences among barley (Hordeum vulgare L.) genotypes in their responses to N starvation and subsequent N re-supply. In this study, two barley genotypes, BI-04 (higher NUE) and BI-45 (lower NUE) were used to investigate N uptake and assimilation at seedling stage in response to N deprivation and re-supply at low (3.75 mM) and normal (7.5 mM) levels. Compared to the continues normal N supply, under N deprivation, both genotypes exhibited less total biomass and N accumulation, but had higher N uptake efficiency, with BI-04 having more biomass, N accumulation and nitrate reductase activity than BI-45. The higher nitrate reductase activity in roots of BI-04 versus BI-45 was associated with up-regulated HvNar1 gene expression under N deprivation condition. NUE of both genotypes was higher under low N re-supply than under normal N re-supply after N deprivation. In addition, glutamine synthetase activity in the two barley roots was higher under low N re-supply than under normal N re-supply, which was associated with the expression of HvGS1_1 and HvGS1_2 genes. Compared to the lower NUE genotype (BI-45), the higher NUE genotype (BI-04) under low N re-supply performed better in response to N stress, and may require relatively less N fertilizer application in production.

Characterization of transgenic Poncirus trifoliata overexpressing the ferric chelate reductase gene CjFRO2 from Citrus junos

Iron deficiency chlorosis occurs frequently in calcareous soils. The transformation of plants with ferric chelate reductase genes (FROs) provides a potential strategy to alleviate plant chlorosis under iron deficiency. A CjFRO2 gene isolated from Citrus junos Sieb. ex Tanaka was introduced into Poncirus trifoliata (L.) Raf via Agrobacterium-mediated transformation. The transgene integration and expression were confirmed by PCR, Southern blot, and real-time PCR analyses. Hydroponic- and soil-grown transgenic plants were tested for their tolerance to iron deficiency. Compared with nontransgenic (NT) P. trifoliata plants, a rhizosphere acidification capacity in the transgenic lines increased, and a ferric chelate reductase activity in roots was up to 3.39- and 2.93-fold higher in a hydroponic solution and soil, respectively. A transgenic line TO-8, which reacted similarly in hydroponics and soil, appeared tolerant to the iron deficiency. Its leaf chlorophyll and ferrous ion content was significantly higher than in NT. These results indicate that tolerance to the iron deficiency in P. trifoliata could be improved through the genetic engineering.

The Effects of Iron Deficiency on Lead Accumulation in Ailanthus altissima (Mill.) Swingle Seedlings

Understanding the effects of root Fe deficiency on the uptake and translocation of toxic metals can be important for improving the phytoremediation strategies of polluted soils. The present study investigated how Fe nutritional status affects the uptake and root-to-shoot-translocation of Pb in hydroponically grown seedlings of (Mill.) Swingle. The interactions of Fe deficiency and Pb were assessed by measuring the root Fe(III) reductase activity, carboxylic acids concentration in root exudates, root and shoot biomass, and accumulation of Pb and other metals (Fe, Zn, Mn, and Cu) in roots and leaves of Fe-sufficient (+Fe) and Fe-deficient (-Fe) plants. The results indicate that Fe deficiency induced 18-fold higher Fe(III) reductase activity in roots compared with +Fe plants, which was followed by increased root exudation of citric acid (28.2 ± 1.39 in +Fe and 498 ± 256.4 μmol g DW 2 h in -Fe plants). Iron deficiency also induces a significant decrease of root and shoot dry weight compared with the control +Fe plants, whereas 2-wk Pb (20 μM) treatment did not influence root and shoot growth. Iron-sufficient plants accumulated more Pb (56.8 ± 17.29 μg g) in leaves than -Fe plants (21.5 ± 8.10 μg g). Two weeks of exposure to Pb significantly decreased Fe(III) reductase activity and accumulation of Fe, Zn, and Mn in the roots of -Fe plants. It is hypothesized that 2 wk of root exposure to Pb blocks functioning of a specific Fe transport system activated under Fe deficiency.

Recent Advances in Research on Japanese Pear Rootstocks

In this paper, I review recent advances in research on Japanese pear rootstocks. Several clones of Pyrus betulaefolia and P. calleryana seedlings have been identified based on their ability to induce dwarfing scion growth, and their use in the future as dwarfing rootstock is anticipated. Among the various rootstock species, P. betulaefolia exhibits good adaptability to different environmental conditions, with high tolerance to drought, cold, and salt. This is due, in part, to P. betulaefolia’s superior ability to regulate osmotic potential and ability to maintain a high degree of unsaturation in fatty acids in biological membranes during cold hardening. P. calleryana exhibits not only a relatively high drought tolerance but also the highest flood tolerance. This tolerance depends on the ability of P. calleryana to shift to alcohol fermentation under anaerobic conditions and to expel the ethanol thus generated. These two rootstock species are highly effective in preventing fruit-hardening disorders. While P. betulaefolia exhibits high salt tolerance among native Asian Pyrus species, it is exceeded in this respect by two native Mediterranean species, P. amygdaliformis and P. elaeagrifolia, with a mechanism to inhibit the transport of salts from the roots to above-ground plant parts. Furthermore, P. xerophila exhibits superior Fe3+-chelate reductase activity in roots, endowing the species with tolerance to alkaline soils.

Nodulation Characteristics, Nodule Nitrogen, and Carbon Dioxide Fixation in Pigeon Pea as Affected by Nitrogen

The legume pigeon pea [Cajanus cajan (L.) Millsp.] is an important rainfed crop in many areas of the world. Production can be reduced when high nitrogen is present and symbiotic activity is low. A field experiment was conducted to determine the effects of nitrogen rate on nodulation, nodule carbon, and nitrogen fixation in 40 pigeon pea genotypes. Nitrogen was applied as urea at 40 (N40) and 120 kg·ha−1 of N (N120). Shoot biomass, root nodulation, amounts of nitrogen and carbon fixed, nitrate reductase activity in roots and nodules, and nitrite content in roots and nodules were determined. Genotype, N rate, and the interaction affected results. The genotypes Pusa-2001 and Sel-90306-11-4 had the most nodule mass at N40. Nitrogen rate did not affect nodule nitrogen-fixing effectiveness. Genotype Pusa-2001 had higher biomass at N120. Genotype Sel-90306-11-4 had high phosphoenol pyruvate carboxylase activity even at N120; which likely reduces host carbon dependence for nodule nitrogen function and improves carbon diversion to the reproductive sink. At N40 ‘Sel-24’ formed large nodules with effective nitrogen fixation, which was impaired at N120. ‘RG-01-69N’ had lower numbers of nodules, nodule mass, and nitrogen fixation but more shoot biomass than the majority of the pigeon pea lines. N-response of pigeon pea was evident for nodule N2 fixation. Genotypes with improved nodule CO2 fixation may lead to increased yield and quality in monocropped and intercropped pigeon pea.

Iron homeostasis and fire blight susceptibility in transgenic pear plants overexpressing a pea ferritin gene

The bacterial pathogen Erwinia amylovora causes the devastating disease known as fire blight in some rosaceous plants including apple and pear. One of the pathogenicity factors affecting fire blight development is the production of a siderophore, desferrioxamine, which overcomes the limiting conditions in plant tissues and also protects bacteria against active oxygen species. In this paper we examine the effect of an iron chelator protein encoded by the pea ferritin gene on the fire blight susceptibility of pear ( Pyrus communis). Transgenic pear clones expressing this gene controlled either by the constitutive promoter CaMV 35S or by the inducible promoter sgd24 promoter were produced. The transgenic clones produced were analysed by Q-RT-PCR to determine the level of expression of the pea transgene. A pathogen-inducible pattern of expression of the pea transgene was observed in sgd24-promoter transformants. Adaptation to iron deficiency in vitro was tested in some transgenic clones and different iron metabolism parameters were measured. No strong effect on iron and chlorophyll content, root reductase activity and fire blight susceptibility was detected in the transgenic lines tested. No transformants showed a significant reduction in susceptibility to fire blight in greenhouse conditions when inoculated with E. amylovora.

Arsenate reductase activity in roots from the arsenic hyperaccumulator Pteris vittata utilizes both glutathione and dithiothreitol as reductants

The role of glutathione and dithiothreitol as reductants supporting arsenate reductase activity in root extract from the arsenic hyperaccumulator Pteris vittata was examined. The two reductants in combination enhanced arsenate reduction in vitro more than glutathione alone. The implications of these results for in vivo arsenate reduction are discussed.

Differential regulatory role of nitric oxide in mediating nitrate reductase activity in roots of tomato (Solanum lycocarpum).

Nitric oxide (NO) has been demonstrated to stimulate the activity of nitrate reductase (NR) in plant roots supplied with a low level of nitrate, and to affect proteins differently, depending on the ratio of NO to the level of protein. Nitrate has been suggested to regulate the level of NO in plants. This present study examined interactive effects of NO and nitrate level on NR activity in roots of tomato (Solanum lycocarpum). NR activity, mRNA level of NR gene and concentration of NR protein in roots fed with 0.5 mM or 5 mM nitrate and treated with the NO donors, sodium nitroprusside (SNP) and diethylamine NONOate sodium (NONOate), and the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO), were measured in 25-d-old seedlings. Addition of SNP and NONOate enhanced but cPTIO decreased NR activity in the roots fed with 0.5 mm nitrate. The opposite was true for the roots fed with 5 mM nitrate. However, the mRNA level of the NR gene and the protein concentration of NR enzyme in the roots were not affected by SNP treatment, irrespective of nitrate pre-treatment. Nevertheless, a low rate of NO gas increased while cPTIO decreased the NR activities of the enzyme extracts from the roots at both nitrate levels. Increasing the rate of NO gas further increased NR activity in the enzyme extracts of the roots fed with 0.5 mM nitrate but decreased it when 5 mM nitrate was supplied. Interestingly, the stimulative effect of NO gas on NR activity could be reversed by NO removal through N(2) flushing in the enzyme extracts from the roots fed with 0.5 mM nitrate but not from those with 5 mM nitrate. The effects of NO on NR activity in tomato roots depend on levels of nitrate supply, and probably result from direct interactions between NO and NR protein.

Contrasting below- and aboveground responses of two deciduous trees to patchy nitrate availability

We investigated how patchy nitrate availability influences growth and functioning of plant roots and generates, through vascular constraints on long-distance transport, aboveground heterogeneity in plant growth and chemistry. We examined two broadleaf tree species, Acer rubrum L. and Betula papyrifera Marsh. Plants were grown either in a split-root setup where a single root received full nutrient supply and the rest of the root system received all nutrients except nitrogen (patchy treatment), or in a single pot with full nutrient supply (homogeneous treatment). In both species, fine roots proliferated in the nitrogen patch, but B. papyrifera produced twice as much fine root biomass in response to patchy nitrate availability as did A. rubrum. There was no difference between treatments in nitrogen uptake rate in either species. In general, specific water uptake was higher in A. rubrum than in B. papyrifera, especially in the nitrogen-rich side pot. When nitrate availability was patchy, nitrate reductase activity in roots and leaves was unaffected in either species. In A. rubrum, but not in B. papyrifera, patchy nitrate supply resulted in aboveground heterogeneity, with leaves above the N-fertilized roots being larger and having a higher relative chlorophyll concentration than those inserted in the opposite quater of the stem.

Effect of Half and Whole Root Drying on Photosynthesis, Nitrate Concentration, and Nitrate Reductase Activity in Roots and Leaves of Micropropagated Apple Plants

Half or whole root systems of micropropagated `Gala' apple (Malus ×domestica Borkh.) plants were subjected to drought stress by regulating the osmotic potential of the nutrient solution using polyethylene glycol (20% w/v) to investigate the effect of root drying on NO3- content and metabolism in roots and leaves and on leaf photosynthesis. No significant difference in predawn leaf water potential was found between half root stress (HRS) and control (CK), while predawn leaf water potential from both was significantly higher than for the whole root stress (WRS) treatment. However, diurnal leaf water potential of HRS was lower than CK and higher than WRS during most of the daytime. Neither HRS nor WRS influenced foliar NO3- concentration, but both significantly reduced NO3- concentration in drought-stressed roots as early as 4 hours after stress treatment started. This reduced NO3- concentration was maintained in HRS and WRS roots to the end of the experiment. However, there were no significant differences in NO3- concerntation between CK roots and unstressed roots of HRS. Similar to the effect on root NO3- concentration, both HRS and WRS reduced nitrate reductase activity in drought-stressed roots. Moreover, leaf net photosynthesis, stomatal conductance and transpiration rate of HRS plants were reduced significantly throughout the experiment when compared with CK plants, but the values were higher than those of WRS plants in the first 7 days of stress treatment though not at later times. Net photosynthesis, stomatal conductance and transpiration rate were correlated to root NO3- concentration. This correlation may simply reflect the fact that water stress affected both NO3- concentration in roots and leaf gas exchange in the same direction.

A copper-deficiency-induced root reductase is different from the iron-deficiency-induced one in red clover (Trifolium pratense L.)

There is increasing evidence that Cu deficiency can induce root reductase activity, but the ecological and physiological significance of this is unknown. This study compared the characteristics of root reductase activity induced by Cu deficiency with those induced by Fe deficiency in red clover (Trifolium pratenseL. cv. Kenland), a Fe-efficient plant. Effects of other nutritional stresses were also investigated for comparison. Compared with the effect of Fe deficiency, Cu deficiency induced only a moderate level of root reductase activity, while other nutrient stresses had no effect, or even inhibited the root reductases activity, especially in the case of Zn deficiency. Compared with Fe deficiency-induced Fe(III)-chelate reductase, Cu deficiency-induced reductase displayed a different pattern of induction. The activity of the Cu deficiency-induced reductase in intact plants increased with time; in decapitated plants it showed a distinct peak at a later stage of the treatment. The Fe concentration in the roots was significantly increased under Cu deficiency. Furthermore, the reductase activity was presented in the entire root system, contrary to what was observed for the Fe-deficiency-induced reductase activity, which was confined to the root apex. Cu deficiency did not increase proton extrusion from the roots, even when growth was significantly affected. The present results suggest that in red clover Cu deficiency induces a root reductase that is different from the reductase induced by Fe deficiency.

Short communication. Nitrate reductase activity in roots and leaves of chickpea cultivars under salt stress

Four chickpea cultivars (CSG 9651, BG 267, CSG 8962 and DCP 92-3) were grown to maturity under salinity conditions of 0, 4, 6 and 8 dS mE-1. Nitrate reductase activity decreased progressively with increasing salinity, although variation was seen between the cultivars. Cultivar CSG 9651, a kabuli or Mediterranean type, appeared to be the best adapted to saline stress, maintaining growth and showing efficient nitrate reduction under these conditions.

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.

Ferric Chelate Reductase Activity in Roots of Two Annona Species as Affected by Iron Nutrition

Root ferric chelate reductase (FCR) activity in Annona glabra L. (pond apple), native to subtropical wetland habitats and Annona muricata L. (soursop), native to non-wetland tropical habitats, was determined under Fe-sufficient and Fe-deficient conditions. Four-month-old seedlings of each species were grown hydroponically in a complete nutrient solution containing 90 μm Fe or no Fe. The degree of tolerance of Fe deficiency was evaluated by measuring root FCR activity, chlorophyll and Fe concentration in recently matured leaves and plant growth. Root FCR activity was higher in soursop than in pond apple in the nutrient solution with Fe. However, there were no differences in root FCR activity between species under Fe-deficient conditions. Root FCR activity in pond apple and soursop was not induced in the absence of Fe. Leaf chlorophyll index and Fe concentration, and dry weights of pond apple were lower when plants were grown without Fe compared to plants grown with Fe. Leaves of pond apple grown without Fe became chlorotic within 3 weeks. Lack of Fe decreased the chlorophyll index and Fe concentration in young leaves less in soursop than in pond apple. In contrast, the Fe level in the nutrient solution had no effect on dry weights of soursop. The rapid development of leaf chlorosis and low FCR activity of pond apple may be due to its native origin in wetland areas where there is sufficient soluble Fe for plant growth and development.