Evaluation of 59Fe-lignosulfonates complexes as Fe-sources for plants

Iron chlorosis is a wide-spread limiting factor of production in agriculture. To cope with this problem, synthetic chelates (like EDTA or EDDHA) of Fe are used in foliar-spray or in soil treatments; however, these products are very expensive. Therefore paper-production byproducts, like Lignosulfonates (LS), with varying content of carboxylate and sulfonate groups, were tested with respect to their ability to maintain Fe in the solution of soils and to feed plants grown in hydroponics with Fe through foliar sprays or application to the nutrient solution. Results show that LS had a low capability to solubilize ⁵⁹Fe-hydroxide and that preformed ⁵⁹Fe(III)-LS complexes had poor mobility through a soil column (pH 7.5) and scarce stability when interacting with soils compared to ⁵⁹Fe(III)-EDDHA. However when ⁵⁹Fe(III)-LS were supplied to roots in a hydroponic system, they demonstrated an even higher capability to fed Fe-deficient tomato plants than ⁵⁹Fe(III)-EDDHA. Hence, data here presented indicate that the low Fe use efficiency from Fe-LS observed in soil-applications is due to interactions of these Fe-sources with soil colloids rather than to the low capability of roots to use them. Foliar application experiments of ⁵⁹Fe(III)-LS or ⁵⁹Fe(III)-EDTA to Fe-deficient cucumber plants show that uptake and reduction rates of Fe were similar between all these complexes; on the other hand, when ⁵⁹Fe(III)-LS were sprayed on Fe-deficient tomato leaves, they showed a lower uptake rate, but a similar reduction rate, than ⁵⁹Fe(III)-EDTA did. In conclusion, Fe-LS may be a valid, eco-compatible and cheap alternative to synthetic chelates in dealing with Fe chlorosis when applied foliarly or in the nutrient solution of hydroponically grown plants.     

Water-extractable humic substances enhance iron deficiency responses by Fe-deficient cucumber plants

The ability of Fe-deficient cucumber plants to use iron complexed to a water-extractable humic substances fraction (WEHS), was investigated. Seven-day-old Fe-deficient plants were transferred to a nutrient solution supplemented daily for 5 days with 0.2 μM Fe as Fe-WEHS (5 μg org. C mL^-1), Fe-EDTA, Fe-citrate or FeCl₃. These treatments all allowed re-greening of the leaf tissue, and partial recovery of dry matter accumulation, chlorophyll and iron contents. However, the recovery was faster in plants supplied with Fe-WEHS and was already evident 48 h after Fe supply. The addition of 0.2 μM Fe to the nutrient solution caused also a partial recovery of the dry matter and iron accumulation in roots of Fe-deficient cucumber plants, particularly in those supplied with Fe-WEHS. The addition of WEHS alone (5 μg org. C mL^-1, 0.04 μM Fe) to the nutrient solution slightly but significantly increased iron and chlorophyll contents in leaves of Fe-deficient plants; in these plants, dry matter accumulation in leaves and roots was comparable or even higher than that measured in plants treated with Fe-citrate or FeCl₃. After addition of the different iron sources for 5 days to Fe-deficient roots, morphological modifications (proliferation of lateral roots, increase in the diameter of the sub-apical zones and amplified root-hair formation) and physiological responses (enhanced Fe(III)-chelate reductase and acidification of the nutrient solution) induced by Fe deficiency, were still evident, particularly in plants treated with the humic molecules. The presence of WEHS caused also a further acidification of the nutrient medium by Fe-deficient plants. The Fe-WEHS complex (1 μM Fe) could be reduced by intact cucumber roots, at rates of reduction higher than those measured for Fe-EDTA at equimolar iron concentration. Plasma membrane vesicles, purified by two-phase partition from root microsomes of Fe-deficient plants, were also able to reduce Fe-WEHS. Results show that Fe-deficient cucumber plants can use iron complexed to water soluble humic substances, at least in part via reduction of complexed Fe(III) by the plasma membrane Fe(III)-chelate reductase of root cells. In addition, the stimulating effect of humic substances on H⁺ release might be of relevance for the overall response of the plants to iron shortage. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of iron plaque outside roots on nutrient uptake by rice (Oryza sativa L.). Zinc uptake by Fe-deficient rice

This solution culture study examined the effect of the deposition of iron plaque on zinc uptake by Fe-deficient rice plants. Different amounts of iron plaque were induced by adding Fe(OH)₃ at 0, 10, 20, 30, and 50 mg Fe/L in the nutrient solution. After 24 h of growth, the amount of iron plaque was correlated positively with the Fe(OH)₃ addition to the nutrient solution. Increasing iron plaque up to 12.1 g/kg root dry weight increased zinc concentration in shoots by 42% compared to that at 0.16 g/kg root dry weight. Increasing the amount of iron plaque further decreased zinc concentration. When the amounts of iron plaque reached 24.9 g/kg root dry weight, zinc concentration in shoots was lower than that in shoots without iron plaque, implying that the plaque became a barrier for zinc uptake. While rice plants were pre-cultured in –Fe and +Fe nutrient solution in order to produce the Fe-deficient and Fe-sufficient plants and then Fe(OH)₃ was added at 20, 30, and 50 mg Fe/L in nutrient solution, zinc concentrations in shoots of Fe-deficient plants were 54, 48, and 43 mg/kg, respectively, in contrast to 32, 35, and 40 mg/kg zinc in shoots of Fe-sufficient rice plants. Furthermore, Fe(OH)₃ addition at 20 mg Fe/L and increasing zinc concentration from 0.065 to 0.65 mg Zn/L in nutrient solution increased zinc uptake more in Fe-deficient plants than in Fe-sufficient plant. The results suggested that root exudates of Fe-deficient plants, especially phytosiderophores, could enhance zinc uptake by rice plants with iron plaque up to a particular amount of Fe.     

Reduction-based iron uptake revisited: On the role of secreted iron-binding compounds

With the exception of the grasses, plants rely on a reduction-based iron (Fe) uptake system that is compromised by high soil pH, leading to severe chlorosis and reduced yield in crop plants. We recently reported that iron deficiency triggers the production of secondary metabolites that are beneficial for Fe uptake in particular at high external pH when iron is present but not readily available. The exact function of these metabolites, however, remains enigmatic. Here, we speculate on the mechanism by which secondary metabolites secreted by roots from Fe-deficient plants improve Fe acquisition. We suggest that the production and excretion of Iron Binding Compounds (IBCs) constitute an integrative, pH-insensitive component of the reduction-based iron uptake strategy in plants.     

Behaviour of iron and manganese chelates in calcareous soils and their effectiveness for plants

Summary The behaviour of the metal chelates Mn-EDTA, Mn-DTPA, Mn-EDDHA, Fe-EDTA, Fe-DTPA and Fe-EDDHA in calcareous soils and their availability to plants were studied. The effectiveness of a metal chelate was shown to depend on its stability, the fixation capacity in the soil and its toxicity to the plant. Incorporation of Fe-DTPA into a framework of silica molecules prevents the fixation of Fe-DTPA in the soil. Fe-DTPA and Fe-EDDHA cause a reduction in the manganese uptake of the plant. The most striking result was the behaviour of Mn-DTPA in calcareous soils. Partial replacement of manganese in the chelate by iron from the soil makes this chelate useful for supplying the plant with both iron and manganese. Mn-DTPA appears to be the ideal type of chelate for the correction of chlorosis in the Netherlands, but unfortunately is not yet commercially available.     

Effect of nitrate nutrition on iron utilization by an Fe-efficient and an Fe-inefficient soybean cultivar

Summary The effects of increasing amount of nitrate nitrogen on the growth, dry matter production, ionic balance and the appearance of iron chlorosis in two soybean cultivars were studied. More nitrogen increased the dry matter production of the Fe-efficient cultivar Hawkeye and decreased that of the Fe-inefficient cultivar T-203. The plants of Hawkeye showed no iron deficiency symptoms whereas all the plants of the Fe-inefficient cultivar T-203 developed Fe deficiency after about one week following emergence. The degree of chlorosis in the cultivar T-203 was more pronounced as the amount of nitrate applied increased.Deceased     

Response of Eucalyptus tereticornis to inoculation with indigenous AM fungi in a semiarid alfisol achieved with different concentrations of available soil P

Eucalyptus tereticornis was grown in a green house in a low phosphorus (0.67 ppm Olsen's P) soil (Typic Haplustalf) inoculated with mixed indigenous arbuscular mycorrhizal (AM) fungi. Soil was amended to achieve P levels of 10, 20, 25, 30 and 40 ppm to evaluate the growth response and dependence of E. tereticornis to inoculation with AM fungi. A positive response to mycorrhizal inoculation was evident at the first two levels of soil P, i.e., at 0.67 and 10 ppm but not at the higher levels of soil P. Dry matter yield of inoculated plants beyond 20 ppm soil P was similar or even less compared to their uninoculated counterparts. Inoculated plants produced maximum dry matter (root and shoot) at 10 ppm soil P, whereas uninoculated plants did not produce until the level reached 20 ppm. The percentage root length colonized by AM fungi decreased from 31% to 3% as the concentration of P increased beyond 10 ppm soil P. Higher levels of soil P depressed the AM colonization significantly. Inoculated plants had higher shoot P and N contents compared to their uninoculated counterparts at all levels of soil P. However, at the first two lower levels of soil P, inoculated plants showed significantly higher shoot P and N contents over their respective uninoculated counterparts. The increasing shoot P accumulation beyond 10 ppm did not enhance dry matter yields. Inoculated plants had lower values of phosphorus utilization efficiency (PUE) and nitrogen utilization efficiency (NUE) at all levels of soil P except at the unamended level (0.67 ppm) where the inoculated plants showed higher values of NUE compared to uninoculated control plants. Taking dry matter yield into consideration, Eucalyptus plants were found to be highly dependent on 10 ppm of soil P for maximum dry matter production. Any further amendment of P to soil was not beneficial neither for AM symbiosis nor plant growth.     

Lolium multiflorum uptake of iron supplied as different synthetic chelates

The plant availability of Fe from synthetic chelates has not been examined extensively for plants having the second strategy in iron uptake. Since these plants also excrete chelating agents, competition between natural and synthetic ligands is expected. This research was conducted to study the efficiency of different iron-chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA and a commercial product, Rexene) inLolium multiflorum iron nutrition. Plants were grown in a greenhouse with hydroponic culture using a buffered nutrient solution at pH 8. Initial iron concentration in the nutrient solution was near 0.5 mgl^–1 and solutions were replaced weekly. In an other Fe-EDTA treatment the same amount of chelate was supplied by four additions during each week.Changes of iron concentration in the nutrient solution, harvestable yield, Fe, Mn, Cu and Zn content in plant tissue and chlorophylllevels in leaves are discussed as parameters to evaluate chelate efficacy. Fe-EDDHA, without inorganic iron in the medium was not as effective as the commercial product Rexene, containing Fe-EDDHA and some extra weakly complex iron, which gave the highest yields. Fe-EDTA applied once a week with fresh nutrient solution was less effective than a four part addition as seen from Chl₁/[Fe] ratios.     

Chlorosis correction and agronomic biofortification in field peas through foliar application of iron fertilizers under Fe deficiency

Effectiveness of different iron (Fe) foliar sprays for leaf chlorosis correction and grain Fe boosting was studied in field peas under Fe deficiency. No chlorophyll reduction was observed in Fe deficient plants treated with foliar sprays. EDDHA [ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid)] followed by FeSO₄ (73.7?mg/l Fe) treated at the start of flowering was most responsive in correcting chlorosis and increasing shoot dry biomass in peas. Inductively coupled plasma-atomic emission spectroscopy data showed significant increase of Fe in grains while treated with all foliar sprays at the time of grain filling in Fe-deficient plants. Among them, FeSO₄ (73.7?mg/l Fe) was the most efficient in biofortifying Fe in mature grain under Fe deficiency in peas. Results also pinpoint that flowering is a suitable time for applying foliar sprays to boost Fe in mature grains. Taken together, application of Fe foliar sprays facilitated both chlorosis correction and Fe boosting in peas and can be further used by breeders and farmers.     

Factors effecting the toxicity of nitrite nitrogen to tomatoes

Experiments were done to study the effects of nitrite nitrogen on nutrient absorption and organic acid content of tomatoes (Keystone) grown in sand culture. The effects of root aeration, magnesium and iron supply on the symptoms of nitrite toxicity were also studied. Nutrient solutions were standardised to pH 4.5 and contained from 0–250 ppm nitrite nitrogen. Increasing the concentration of nitrite nitrogen decreased dry matter yields, total acidity, the concentration of nitrogen, phosphorus and potassium in tomato plants, and increased the chlorosis of leaves and the lignification of roots. Shortage of iron, magnesium, and poor root aeration caused toxicity symptoms to appear at a smaller concentration of nitrite nitrogen and increased the severity of the symptoms.     

Bicarbonate concentration as affected by soil water content controls iron nutrition of peanut plants in a calcareous soil.

Strategy I peanut plants are frequently subjected to iron deficiency when growing in calcareous soils, which contain high concentrations of bicarbonate. In calcareous soils under field conditions, it has been noted that chlorosis increases in severity after excessive rainfall or irrigation, but the chlorosis symptoms of peanuts are alleviated after waterlogged soils dry. A pot experiment was conducted simulating the chlorosis symptom observed in the field when peanut plants are exposed to fluctuating soil water content induced from rainfall or irrigation. We investigated the bicarbonate fluctuations resulting from adjustable soil water content (SWC) that could lead to bicarbonate-induced iron chlorosis of peanuts growing in calcareous soil. The experiments included three treatments of SWC (50% of water holding capacity (WHC), 80% of WHC, and 100% of WHC) under two levels of CaCO(3) concentrations (at 8.67% and 18.67%.) The results showed that the iron nutrition of peanuts could be regulated by different SWC at both CaCO(3) levels. Our observations indicate that iron deficiency chlorosis symptoms in peanuts grown in high soil water content were more severe, compared to those of peanuts in lower soil water content. A shift from high soil water content to lower soil water content could improve or eliminate the iron deficiency chlorosis symptom of peanuts. The HCO(3)(-) concentration in the peanut rhizosphere increased with increasing SWC and CaCO(3) content and it correlated with the level of soil water content. We suggest that variations in the soil water content could induce HCO(3)(-) concentration variation in the rhizosphere of peanuts. Consequently, the high HCO(3)(-) concentration, which is induced by a high water content in calcareous soil and a high CaCO(3) level, could inhibit the physiological response to iron deficiency of peanuts, resulting in iron deficiency chlorosis. The study indicates that a reasonable agricultural practice of irrigation and drainage should be considered to improve and prevent iron deficiency chlorosis of strategy I plants in calcareous soil.     

An Exogenous Source of Nitric Oxide Modulates Iron Nutritional Status in Peanut Seedlings (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

Iron (Fe) deficiency chlorosis is a common and severe nutritional deficiency in plants, and nitric oxide (NO) is an important signaling molecule in regulating Fe homeostasis in plants. We studied the effect of sodium nitroprusside (SNP, an NO donor) on Fe uptake, translocation, storage, and activation in a greenhouse. The concentrations of active Fe, total Fe, and the ratio of active Fe to total Fe, the activities of key enzymes, and chlorophyll concentration were determined, and resistance to oxidative stress and mineral element distribution in peanut plants grown in Fe sufficiency and Fe deficiency (an absence of Fe and low level of Fe concentration) conditions were also investigated. The results showed that NO significantly increased the concentration of active Fe and the ratio of active Fe to total Fe in Fe-deficient plants, and increased active Fe concentration in leaves and stems of Fe-sufficient plants. NO application also increased Fe translocation from roots to the shoots and the accumulation of Fe in cell organelles and the soluble fraction in leaves, especially in the low-level Fe concentration condition, thus increased available Fe and chlorophyll concentration in leaves of Fe-deficient plants. The activities of key enzymes were regulated by NO, which effectively mitigated oxidative damages by enhancing the activities of antioxidant enzymes (SOD, POD, CAT), increasing H⁺-ATPase and Ca²⁺-ATPase activities to balance the ion (Fe, Ca, Mg and Zn) uptake and distribution in Fe-deficient plants. However, NO application had no obvious effect on these variables in Fe-sufficient plants. These results indicated that NO application can improve Fe uptake, translocation, and activation of related enzymes in Fe-deficient plants, thus mitigating the adverse effect of Fe deficiency.     

Comparative efficacy of sulphuric acid and sequestrene 138Fe foliar sprays in the prevention of chlorosis in corn (Zea mays,L.)

Summary Results of two pot experiments comprising foliar sprays of sulphuric acid and sequestrene 138 Fe alone and in combination with elemental sulphur with calcareous soils of Agronomy farm of the College of Agriculture, Udaipur showed that the application of elemental sulphur, sulphuric acid and sequestrene 138 Fe increased the dry matter yield of corn plants in the order named. These treatments increased the activities of haematin enzymes-catalase and peroxidase two to three times and also the chlorophyll content. Iron chlorosis in these conditions appears to be on account of reduced supply of physiological available iron at the site of biosynthesis of prophyrins in the plant system.     

Determination of threshold value of iron in soils and plants for the response of rice and lentil to iron application in calcareous soil

Summary In a pot experiment with 26 calcareous soils, the critical limit of Fe in soils and plants was evaluated. DTPA-extractable Fe was found significanty correlated with Bray's per cent yield in rice. The Fe²⁺ (iron) in rice and lentil was also found significantly correlated with DTPA-extractable Fe as well as Bray's per cent yield showing thereby the superiority of Fe²⁺ (iron) in leaves over DTPA-extractable soil Fe to differentiate Fe responsive soils from non-responsive ones. The total Fe content in plant tissues does not seem correlated with the occurrence of Fe deficiency. The threshold values of DTPA-extractable soil Fe and Fe²⁺ (iron) in rice and lentil leaves were 6.95, 44 and 74.5 ppm, respectively below which appreciable responses to Fe application were observed. The optimum Fe level for these soils was found to be 10 ppm in which the dry matter yield response in all the 19 rice soils and 16 lentil soils ranged from 14.28 to 56.16 (Av. 25.75%) and 13.31 to 53.97 (Av. 22.47%), respectively.     

Iron deficiency in lentil: Yield loss and geographic distribution in a germplasm collection

Iron deficiency symptoms are observed on some genotypes of lentil (Lens culinaris Medikus) grown in calcareous soil. A germplasm collection of 3512 accessions originating from 18 countries was characterized for iron deficiency in a Calcic Rhodoxeralf soil at ICARDA, Tel Hadya, Syria in the 1979/80 season. At 105 days after sowing, 592 accessions, representing 16.9% of the collection, showed chlorosis symptoms characteristic of iron (Fe) deficiency. The Fe deficiency was verified by foliar application of Fe-chelate. Germplasm from different countries showed differences in iron deficiency, with those accessions exhibiting symptoms of iron deficiency mostly originating from relatively warm climates such as India (37.5% accessions showing Fe deficiency) and Ethiopia (30%). Populations from those Mediterranean countries where lentil originated (Syria and Turkey) exhibited Fe-deficiency symptoms only at very low frequencies. Fe-deficiency induced chlorosis was positively correlated with cold susceptibility. Fe chlorosis was transient, the deficiency symptoms largely disappearing during reproductive growth at a time, coinciding with increases in soil temperature and daylength-conditions favorable for plant growth. In Indian germplasm, mild deficiency symptoms did not lead to reduced seed yield, but there was a major yield reduction of 47% in those accessions with the most severe symptoms. Straw yields was reduced commensurately with the severity of symptoms. ei]Section editor: B G Rolfe     

Effects of heavy metals on both induction and function of root Fe(lll) reductase in Fe-deficient cucumber (Cucumis sativus L.) plants

Heavy metals are known to induce Fe chlorosis in different plantspecies. Heavy-metal-induced chlorosis is generally correlatedwith low plant Fe contents, suggesting effects of heavy metalson Fe mobilization and uptake. Under Fe-deficient conditions,dicotyledonous plants enhance root Fe(lll) reductase activity,thus increasing the capacity to reduce Fe(MI) to Fe(ll), theform in which roots absorb Fe. We studied the effect of severalheavy metals (Mn, Pb, Zn, Mo, Ni, Cu, and Cd) on the inductionof enhanced root Fe(lll) reductase by 11-d-old Fe-deficientcucumber [Cucumis sativus L. cv. Ashley). The effect of theseheavy metals on the function of the induced Fe(lll) reductasewas also investigated. Results showed that some heavy metalscan inhibit both the induction and function of root Fe(lll)reductase. Ni, at 20//M, and Cu and Cd, at 5 fiM concentrationor higher, severely inhibited the induction of root Fe(lll)reductase while Mn, Pb, Zn, and Mo had little effect, even atconcentrations higher than 20 //M. Function of the induced rootFe(lll) reductase only was negatively affected by Cu and Ni. Key words: Cucumis sativus, iron deficiency, iron reduction, heavy metals     

Maize ZmFDR3 localized in chloroplasts is involved in iron transport

Iron is an essential nutrient for plant metabolism such that Fe-limited plants display chlorosis and suffer from reduced photosynthetic efficiency. Differential display previously identified genes whose expression was elevated in Fe-deficient maize roots. Here,we describe the functional characterization of one of the genes identified in the screen,ZmFDR3 (Zea maize Fe-deficiency-related). Heterologous functional complementation assays using a yeast iron uptake mutant showed that ZmFDR3 functions in iron tra...     

Effect of salinity,alkalinity and iron application on the availability of iron,manganese, phosphorus and sodium in pea (Pisum sativum L.) crop

Summary The effect of the salinity, alkalinity and Fe application on the dry matter yield and availability of Fe, Mn, P and Na were studied in the greenhouse on pea (Pisum sativum L.) crop. The highest dry matter yield was recorded in normal soil which decreased with the increase in the salinity and alkalinity, minimum being at 40 ESP. Alkalinity was more harmful to pea crop than salinity.Fe at 10 ppm increased the dry matter yield significantly. Highest Fe concentration (408.12 ppm) was recorded in 40 ESP soil followed by 20 ESP (395.2 ppm). Salinity alongwith marginal or higher alkalinity reduced harmful effect of alkalinity. The uptake of Fe was the highest in normal soil due to the high dry matter yield. All the three sources increased the concentration of Fe and its uptake than the control in all the soils but did not show much distinction among themselves.The concentration of Mn decreased more with the increase in alkalinity than salinity but salinity with alkalinity improved Mn concentration. Similarly uptake of Mn also decreased sharply with the increase in salinity and alkalinity. The application of Fe sources decreased Mn concentration but increased the uptake. The highest decrease was caused with FeSO₄ and lowest with Fe rayplex.Like Mn the concentration and uptake of P decreased with the increased levels of salinity and alkalinity. The addition of Fe decreased the concentration of P, highest depression being with Fe KE-MIN.Increase in ESP increased the concentration and the uptake of Na greatly. Addition of Fe through all the sources increased Na concentration and uptake significantly but sources did not differ much in their effect on Na.     

Iron deficiency in peach trees: effects on leaf chlorophyll and nutrient concentrations in flowers and leaves

The effects of iron deficiency on the leaf chlorophyll concentrations and on the macro- (N, P, K, Ca and Mg) and micro-nutrient (Fe, Mn, Zn and Cu) composition of flowers (at full bloom) and leaves (60 and 120 days after full bloom) of field-grown peach (Prunus persica L. Batsch) trees were investigated. Flowers and leaves were taken and analysed from fifty individual trees. Our data indicate that large decreases in leaf chlorophyll concentration were found at the beginning of the season in control trees, possibly associated to a dilution effect by leaf growth, that were later followed by leaf chlorophyll concentration increases. Leaf Fe chlorosis apparently results from two different processes, the dilution of leaf Chl caused by growth and the subsequent inability to produce and/or stabilize new Chl molecules in the thylakoid membrane. Iron chlorosis did not change the seasonal change patterns of any of the nutrients studied. In Fe-deficient trees the K concentration and the K/Ca ratio were high not only in leaves but also in flowers, indicating that this is a characteristic of Fe-deficient plant tissue in the whole fruit tree growing season. Flower Fe concentrations were well correlated with the degree of chlorosis developed later in the season by the trees, suggesting that flower analysis could be used for the prognosis of Fe deficiency in peach.