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Reza Saeedi, Nematollah Etemadi, Ali Nikbakht, Amir H. Khoshgoftarmanesh and Mohammad R. Sabzalian

inorganic sources of calcium, e.g., Ca(NO 3 ) 2 .4H 2 O, are applied during winter or early spring production to prevent calcium deficiency ( Dole and Wilkins, 2004 ). Recently, Ca-amino acid chelates have been synthesized and distributed to supply different

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Li-Xiao Yao, Yong-Rui He, Hai-Fang Fan, Lan-Zhen Xu, Tian-Gang Lei, Xiu-Ping Zou, Ai-Hong Peng, Qiang Li and Shan-Chun Chen

into strategy I or strategy II plants ( Eide et al., 1996 ; Robinson et al., 1999 ; Romheld, 1987 ; Romheld and Marschner, 1986 ). Strategy II plants include grasses with roots that secrete compounds known as phytosiderophores (PS), which chelate Fe

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Uttara C. Samarakoon and James E. Faust

phytotoxicity symptoms. Chelated Ca that contains ethylenediaminetetraacetate (EDTA) can improve Ca absorption at lower Ca concentrations with root uptake ( Nelson and Niedziela, 1998 ), as well as with foliar applications ( Tang et al., 2007 ). The commercial

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Charalambos I. Siminis and Manolis N. Stavrakakis

(III) to the bioavailable ferrous form [Fe(II)] is required before the transmembrane import of iron ( Marschner and Römheld, 1994 ). In strategy II plants (graminaceous species), soil Fe(III) is chelated and transferred by the plant

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Joseph P. Albano

as ligands or chelating agents. These compounds, especially EDTA, are widely used in an array of domestic, medical, industrial, and agricultural purposes where complexation of multivalent metals in a system is desired. The primary drawback of

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Bruce W. Wood

glyphosate ( Yamada et al., 2009 ). Iron fertilizers are typically “chelates” that bind Fe 3+ (ferric, or oxidized Fe). A common form is Fe-DPTA. Iron (Fe 3+ ) chelates bind to the cytoplasmic plasmalemma, where, in dicots, sequestered Fe 3+ is chemically

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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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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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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

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.