Ferritin gene expression has been demonstrated in a variety of plants including maize, Arabidopsis, cowpeas, soybeans, beans and peas. Most available evidence shows that the mature protein is located in plastids and its production is under gene transcriptional control. In maize, two different ferritin genes have been identified; they were found to express protein under different physiological conditions. Only single gene products have been found until now in the other plants, with the exception of cowpeas (Vigna unguiculata). Our previous work with cowpeas [Wicks and Entsch (1993) Biochem. Biophys. Res. Commun. 192, 813-819] showed the existence of a family of at least three ferritin genes, each coding for a protein subunit with a unique amino acid sequence. Here we report the discovery of a fourth active gene in cowpeas and present the full cDNA sequences for two of the four known members of the cowpea gene family. We also provide preliminary evidence for a family of ferritin genes in soybeans (Glycine max) related to that in cowpeas. We conclude that a family of genes is probably present in all higher plants. We have used quantitative reverse transcriptase-mediated PCR to show that each of the four members of the cowpea ferritin gene family expresses mRNA in leaves and roots under normal growth with a complete nutrient supply. The results clearly show a marked differential pattern of mRNA levels formed during development from the four genes. We conclude that the composition of plant ferritin molecules from plant leaf extracts is probably a complex mixture of subunits, which might be different in roots and in leaves.

Soluble auxin-binding proteins (ABPs) were purified to constant specific activity from bean and pea leaves by a procedure involving (NH4)2SO4 fractionation, anion exchange chromatography and gel filtration. Pea and bean ABPs exactly co-purify with ribulose-1,5-bisphosphate carboxylase (RuBPCase) Auxin-binding sites are associated with membranes isolated from coleoptiles and primary leaves of Zea mays (1, 2, 5-7, 13, 19, 20, 26-28, 31), epicotyls and roots of Pisum sativum (8), soybean hypocotyls (36), mung bean hypocotyls (18), and zucchini hypocotyls (16). Solubilization of such auxin-binding sites from Z. mays has been achieved (5, 7, 31). The solubilized microsomal auxin-binding protein from Z. mays has a specificity for natural and synthetic auxins that parallels the ligand specificity of the membrane-associated protein and the biological activities of the auxin analogues tested (5). On current evidence this membraneassociated auxin-binding protein may well be the (an) auxin receptor. In the absence of evidence for an auxin-induced functional change in this protein the possibility exists that this protein has other than a receptor function. Apparently soluble auxinbinding proteins have been reported (15,21,29,32) Primary bean seedling leaves were excised from seedlings 8-14 days after sowing the seed, washed with distilled H20, and sliced with scissors. All subsequent operations were carried out at 0-4 C.The sliced leaves were suspended in five volumes of an extraction medium containing 50 mm Tris (Cl-, pH 8.0), 10 mm EDTA, 0.1% (v/v) 2-mercaptoethanol, 0.5 mm PMSF, and 0.2% (v/v) ethanol, and homogenized at stop I in a Waring Blendor for I min. The homogenate was filtered through Miracloth and the filtrate centrifuged at 35,000g for 40 min. The supernatant was brought to 30% (NH4)2SO4 saturation, the resulting precipitate being collected by centrifugation and discarded. The resulting supernatant was brought to 50% (NH4)2SO4 saturation and the precipitate collected by centrifugation and dissolved in a minimum volume of buffer A containing 50 mm Tris (Cl-, pH 8.0), 10 mM EDTA, and 0.1% (v/v) 2-mercaptoethanol. This solution was applied to a column (2.5 cm2 x 70 cm) of Ultrogel AcA-34 and eluted with buffer A (Fig. la). The IAA-binding fractions were pooled and applied to a column (4.0 cm2 x 9.0 cm) of DEAE-Sephacel equilibrated with buffer A. The DEAE-Sephacel column was eluted with a linear gradient from 0 to 0.25 M (NH4)2SO4 (in buffer A) (Fig. Ib). The active fractions were pooled, concentrated by precipitation at 80%1o (NH4)2SO4 saturation, and reapplied (in buffer A) to the Ultrogel AcA-34 column and eluted in buffer A. One protein peak associated with a constant specific activity IAA-binding activity peak is observed at this stage (Fig. Ic). The purification schedule is presented in Table I. The same scheme was applied to the purification of ABP from the leaves of pea seedlings. Pea leaves were harvested 10-14 days after sowing the seed. Variants of this basic purification schedule were emp...

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