Comparative evaluation of factors involved in Fe stress response in tomato and soybean

Abstract

KEY WORDS:Iron efficient, Iron inefficient, Iron-stress response mechanism, reductant, reduction of Fe 3+ by roots, root exudates, solution pH. ABSTRACT Iron-efficient and Fe-inefficient tomato (Lycopersicon esculentum Mill; T3238FER and T3238fer, respectively) and soybean (Glycine max (L.) Merr.; A7 and T203, respectively) were grown in modified Hoagland solutions with varying levels of Fe (0, 0.025, 0.05, and 0.75 mg Fe L -1 ). The release of H + ions, reductants and reduction of Fe 3+ to Fe 2+ by the root, and concentration of nutrients in plant leaves and roots were measured to determine if these factors interact during the Festress response mechanism. The FER tomato responded to Fe stress by increasing H ion and reductant release concurrently with increased reduction of Fe 3+ by the roots; all three reached maximum levels at the same time (day 7). Iron-stressed A7 soybean responded first with increased H + ion release and reduction by the roots, while reductant release lagged about 1 day behind. In both cases, increased concentration of leaf Fe corresponded to the time of maximum Fe-stress response. The Fe-423 424 CAMP, JOLLEY, AND BROWN inefficient T3238fer tomato and T203 soybean did not show any of these responses. When soybean plants (A7) were under Fe stress and then received either 0 or 0.20 mg Fe L -1 , the Fe-stressed plants responded to added Fe by reduced levels of H + ion and reductant release and reduction of Fe by the roots.We propose that the three steps of the Fe stress response mechanism--release of H + ions, release of reductants, and reduction of Fe 3+ by the roots--work together to favor maximum reduction of Fe 3+ . The H + ions provide maximum solubility of Fe, reduction by the roots provides reduced Fe, and reductants in the roots provide the environment to maintain the reduced Fe 2+ in the root.

Phytophthora erythroseptica (Pink Rot) Development in Russet Norkotah Potato Grown in Buffered Hydroponic Solutions I. Calcium Nutrition Effects

“…The pretreatment mg L −1 mineral concentrations were 10.94 N, 11.96 P, 14.0 K, 6.1 S, 5.5 Ca, 2.8 Mg, 0.46 Fe, 4.08 Cl, 0.074 Mn, 0.041 B, 0.006 Mo, 0.023 Zn, 0.006 Cu, 0.003 Na (Camp et al 1987 (Camp et al 1987). Calcium treatment concentrations were varied using Ca (NO 3 ) 2 at 2.9, 85.9, 171.8, 343.6 mg L −1 .…”

“…Roots of four to six cm length plantlets (20 total plants per 14 L −1 tank) were placed into a modified Steinberg pretreatment solution containing a minimal level (5.5 mg L −1 ) of Ca to avoid luxury consumption of this nutrient by plantlets (Camp et al 1987). The pretreatment mg L −1 mineral concentrations were 10.94 N, 11.96 P, 14.0 K, 6.1 S, 5.5 Ca, 2.8 Mg, 0.46 Fe, 4.08 Cl, 0.074 Mn, 0.041 B, 0.006 Mo, 0.023 Zn, 0.006 Cu, 0.003 Na (Camp et al 1987 (Camp et al 1987).…”

Effect of Pseudomonas fluorescens on the root exudates of two tomato mutants differently sensitive to Fe chlorosis

“…mutants T3238FER and T3238fer are chlorosisresistant and -susceptible plants, respectively, which in a non-sterile rooting medium differ in their ability to reduce rhizosphere pH and exudation of Fe-reducing compounds by their roots (Camp, Jolley and Brown, 1987;Olsen et al, 1981). We cultured the roots of these mutants and noted that under sterile conditions they possess similar Fe uptake properties.…”

Phytophthora erythroseptica (Pink Rot) Development in Russet Norkotah Potato Grown in Buffered Hydroponic Solutions II. pH Effects

“…Roots of four to six cm length plantlets (20 total plants per 14 L −1 bucket) were placed into a modified Hoagland pretreatment solution containing: mg L −1 concentrations were 90.1 N, 7.74 P, 93.6 K, 11.5 S, 85.9 Ca, 8.68 Mg, 1.5 Fe, 3.34 Cl, 0.37 Mn, 0.204 B, 0.029 Mo, 0.114 Zn, 0.029 Cu, 0.014 Na (Camp et al 1987). After 14 days in the pretreatment solution, 16 uniform sized plants per bucket were randomly transferred into a modified Hoagland treatment solution containing the same mineral concentration listed above except for K that had 93.6 mg L −1 for pH 5.0, 98.6 mg L −1 for pH 6, 109.6 mg L −1 for pH 7, and 120.6 mg L −1 for pH 8.…”