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B. Castillo, D.L. Madhavi, and M.A.L. Smith

Interaction between irradiance levels (5–40 mMm–2–s–1) and iron chelate sources (FeNa2EDTA and FeNaDTPA) on the establishment, growth, and proliferation of shoot tips of Carica papaya were tested. Reduced irradiance level (5 mMm–2–s–1) enhanced the establishment of shoot tips regardless of the source of iron chelate tested. At higher irradiance levels (30 and 40 mMm–2–s–1), presence of FeNaDTPA in the medium enhanced establishment of shoot tips. Continuous or alternating light/dark (16/8 h) photoperiods at high irradiance levels had no effect on the establishment or growth of the culture. At higher irradiance levels, the cultures produced smaller leaves as compared to lower irradiance levels. Low irradiance and FeNa2EDTA was preferred during the proliferation stage.

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B. Castillo, M.A.L. Smith, D.L. Madhavi, and U.L. Yadava

Interactions between irradiance levels (5–40 μmol·m-2·s-1) and iron chelate sources (FeEDTA and FeEDDHA) were observed for Carica papaya shoot tip cultures during both the establishment and proliferation stages of microculture. Reduced levels of irradiance (5 μmol·m-2·s-1) favored shoot tip establishment regardless of the source or level of iron. However, the highest percentage of successful explant establishment (100%), and significantly greater leaf length (1.16 cm; over double the size attained in any other treatment), resulted when a low concentration of FeEDTA alone was used at low irradiance. During the subsequent shoot proliferation stage, however, higher irradiance levels (30 and 40 μmol·m-2·s-1) were required, and FeEDTA failed to support culture growth when used as the sole iron source. The highest multiplication rates (3.6 shoots per explant) and leaf chlorophyll concentrations (0.22 mg/g fresh mass), and significantly improved shoot quality were achieved at 30 μmol·m-2·s-1 irradiance when both iron chelate formulations were combined (each at a 100 μM concentration) in the proliferation medium. Chemical names used: benzylamino purine (BA); ferric disodium ethylenediamine tetraacetate or FeNa2EDTA (FeEDTA); ferric monosodium ethylenediamine di(o-hydroxyphenylacetate), (FeNaEDDHA) or Sequestrene 138Fe (FeEDDHA); indoleacetic acid (IAA); 1-naphthaleneacetic acid (NAA).

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Joseph P. Albano and William B. Miller

Iron chelate photodegradation is a problem in tissue culture where limited soluble Fe in agar reduces callus tissue growth. Our objectives were to determine if Fe chelate photodegradation occurs in commercial fertilizers used in greenhouse plant production and, if so, the effects on plant Fe acquisition. Commercial 20N–10P–20K soluble fertilizers containing Fe-EDTA were prepared as 100x stocks based on a 100 mg N/liter (1x) concentration. A modified Hoagland's solution with Fe-DTPA was prepared as a 10x stock based on a 200 mg N/liter (1x) concentration. Samples then were kept in darkness or were irradiated with 500 μmol·m–2·s–1 from fluorescent and incandescent sources for ≤240 hours. Soluble Fe in the irradiated commercial fertilizer solutions decreased 85% in 240 h. Soluble Fe in the Hoagland's solution, prepared in the lab, decreased 97% in 72 h. There was no loss in soluble Fe in any dark-stored treatment; demonstrating photodegradation of Fe-chelates under commercial settings. Excised roots of marigold (Tagetes erecta L.), grown hydroponically in the irradiated solutions, had Fe(III)-DTPA reductase activity 2 to 6 times greater than roots of plants grown in solutions kept in darkness. Plants growing in irradiated solutions acidified the rhizosphere more than plants growing in solutions kept dark. The increase in Fe reductase activity and rhizosphere acidification are Fe-efficiency reactions of marigold responding to the photodegradation of Fe-chelates and subsequent decrease in soluble Fe in both commercial fertilizers and lab-prepared nutrient solution.

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Joseph P. Albano and William B. Miller

Irradiation of, ferric ethylenediaminetetraacetic acid (FeEDTA, iron chelate)-containing commercial fertilizer solutions by fluorescent plus incandescent lamps resulted in the loss of both FeEDTA and soluble iron (Fe), and the formation of a yellow-tan precipitate that was mostly composed of Fe. The ratio of soluble Fe:manganese (Mn) was altered due to FeEDTA photodegradation from 2:1 in the nonirradiated solutions to 1:4 in the irradiated solutions, respectively. Storing fertilizer solutions in containers that were impervious to light prevented FeEDTA photodegradation.

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Joseph P. Albano and William B. Miller

We have shown previously that Fe-chelates incorporated into soluble fertilizers are vulnerable to photodegradation, and that such solutions can cause modifications in root reductase activity. The objective of this research was to determine the effects of Fe-chelate photodegradation under commercial production conditions. Marigolds were grown in a greenhouse and transplanted stepwise from #200 plug trays to 804 packs to 11.4-cm (4.5-inch) pots. Plants were harvested at the end of each stage, and treatments consisted of either irradiated (complete loss of soluble Fe) or non-irradiated fertilizer solutions ranging from 100-400 mg/L N (0.5–2 mg/L Fe). In the plug and pack stages, foliar Fe was significantly lower and Mn significantly higher in plants treated with the irradiated than nonirradiated fertilizer solutions, averaging 97 μg·g–1 and 115 μg·g–1 Fe, and 217 μg·g–1 and 176 μg·g–1 Mn, respectively. Fe(III)-DTPA reductase activity of roots of plugs treated with the irradiated fertilizer solution was 1.4-times greater than for roots treated with the non-irradiated fertilizer solution. Leaf dry weight in the plug and pack stages was not affected by treatment, and averaged 0.1 g and 1.2 g per plant, respectively.

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Joseph P. Albano and William B. Miller

Our objective was to determine the effects on plant growth and physiology that a photodegraded Fe-chelate containing lab-prepared nutrient solution would have when used in plant culture. Plants grown hydroponically in the irradiated Fe-DTPA containing nutrient solution had ferric reductase activity 2.2 times greater, foliar Fe level 0.77 times less, and foliar Mn level 1.9 times greater than in plants grown in an identical but non-irradiated solution, indicating that plants growing in the irradiated solution were responding to Fe deficiency stress with physiological reactions associated with Fe efficiency. The youngest leaves of plants that were grown in the irradiated solution had symptoms of Mn toxicity. Restoration of the irradiated solution by removing the precipitated Fe by centrifugation and adding fresh Fe-chelate resulted in plants that were, in general, not different from those grown in the non-irradiated solution (control).

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Lisa C. Berg and Henry R. Owen

Nicotiana tabacum callus growth (fresh weight) was measured after culture in the light (16-hour photoperiod) or in darkness for four different culture media, differing in iron chelate type or concentration. All media contained MS basal medium supplemented with 30 g·L–1 sucrose, 2 mg·L–1 IAA, 0.2 mg·L–1 KIN, and 7 g·L–1 agar, pH 5.8. Three of the media contained iron-metalosate (Albion Laboratories), an organic iron chelate, at 100, 200, and 400 micromolar concentrations, and the fourth medium contained 100 μm Fe-EDTA. Twenty-five culture tubes were prepared for each of the 4 different media concentrations and 2 light treatments (8 treatments total). A 1-cm3 callus explant was used for each treatment and cultured for 56 days at 20°C. About 20-fold increases in callus fresh weight were observed for cultures incubated in light or in darkness. In addition, callus growth was not significantly affected by iron chelate type, suggesting the potential utility of this organic chelator in tissue culture media to alleviate potential problems of light-induced EDTA instability and subsequent IAA inactivation. These cultures are being maintained to examine the influence of iron chelate type on organogenesis.

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A.M. Akl, Faissal F. Ahmed, Farag M. El-Morsy, and Mohamed A. Ragab

The effect of single or combined application of urea-formaldehyde at 80 g N/vine, sulfur at 0.4%, and three compounds of iron (chelated, sequestered, and sulfate forms as 0.1%) on productivity of `Red Roomy' grapevines was studied during 1995 and 1996. A substantial increase in berry set, number of clusters, yield weight of clusters and berries, total soluble solid sugars, and anthocyanins was observed because of the application of these fertilizers singly or in combination. Total acidity in the juice was reduced because of application of these fertilizers. Combined application of urea-formaldehyde, sulfur, and chelated iron gave the best results with regard to yield and quality of berries. An economical yield was obtained on `Red Roomy' vines supplied with urea-formaldehyde at 80 g/vine, sulfur at 0.4%, and chelated iron at 0.1%.

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Ritu Dhir, Richard L. Harkess, and Guihong Bi

Bleaching of the youngest leaves of actively growing ivy geranium (Pelargonium peltatum L.) develops as the temperature increases from late spring to summer in the southeastern United States. Heat stress-induced iron deficiency has been suspected as causing this disorder. Ivy geranium ‘Beach’ (bleaching-resistant) and ‘Butterfly’ (bleaching-susceptible) were grown for 8 weeks at 24 or 31 °C average root-zone temperature and iron chelate (Fe-EDDHA, 6% Fe) was applied at 0 mg Fe (control), 0.54 mg Fe foliar spray, 1.08 mg Fe foliar spray, 54 mg Fe drench, or 108 mg Fe drench per plant at 30-day intervals. In a second experiment, ivy geranium ‘Beach’ and ‘Butterfly’ plants were grown for 6 weeks at 28 °C day/16 °C night or 36 °C day/22 °C night average air temperatures and iron chelate (Fe-EDDHA, 6% Fe) was applied at 0 mg (control) or 27 mg Fe soil drench per pot at 15-day intervals. No bleaching was observed as a result of elevated root-zone temperatures. High levels of Fe-chelate suppressed growth reducing fresh weight, dry weight, and fresh-to-dry-weight ratio in ‘Butterfly’. Elevated air temperatures severely reduced plant growth, leaf area, fresh weight, and dry weight in both cultivars. Elevated air temperature reduced chlorophyll a, carotenoids, and pheophytins in ‘Butterfly’ but not in ‘Beach’. Fe-chelate application had no effect at ambient temperature but increased chlorophyll to carotenoids ratio (Chl:Caro) at elevated air temperatures in ‘Butterfly’. Therefore, elevated air temperatures were determined to be the cause of bleaching in ivy geranium.

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Mary C. Halbrooks and Joseph P. Albano

A specific physiological disorder of the recently matured leaves of Tagetes erecta has been demonstrated to be associated with high levels of iron and manganese in affected tissues. In previous work by the authors, the disorder was inducible and increased in severity with increasing levels of iron DTPA supplied to plants grown in peat-based media, but was much less severe when iron DTPA treatments were applied to plants grown hydroponically. At low concentrations of iron DTPA in solution, the occurrence of the disorder was more closely correlated with increased levels of manganese in leaf tissue than iron, Objectives of this study were to determine the effects of iron chelate (DTPA) on occurrence of the disorder and the availability of iron and manganese in the media in the absence of added manganese. Iron DTPA (1, 5, 15, and 20 ppm) was supplied to two cultivars of Tagetes erecta, `Voyager' and `First Lady', grown in a commercial peat-based media product under controlled environmental conditions. Concentrations of iron and manganese in leachate samples taken weekly, and in symptom and non-symptom tissue at harvest, and the progression of the symptoms in leaf tissue over time. will be discussed.