Localization of Ferredoxin Isoproteins in Mesophyll and Bundle Sheath Cells in Maize Leaf

Abstract

MATERIALS AND METHODS Four ferredoxin isoproteins were identifed in the C4 plant Zea mays L. by analysis of extracts from leaves, mesocotyls, and roots of the young seedlings. The relative amounts of the isoproteins isolated from the photosynthetic and nonphotosynthetic organs were different. All the isoproteins were present in the leaves of green and etfolated plants, whereas two out of the four isoproteins were not detected in the roots or in the mesocotyls. During the greening of effolated seedlings, the level of the two isoproteins unique to the leaf increased markedly. Analysis of the cellular and subcellular distribution of the two major leaf isoproteins showed that one isoprotein was present in the chloroplasts of both mesophyll and bundle sheath cells, whereas the other was only found in the chloroplasts of bundle sheath cells. This is the first report of the cell-specific expression of ferredoxin isoproteins in the leaves of a C4 plant.The presence of different molecular species of plant-type Fd in one organism has been reported in a variety of higher plants and algae (4,7,11,15,17), and variations in the Fd isoproteins with stages and conditions of growth have been observed (4,17,20). Although several attempts have been made to examine whether the Fd isoproteins have different functions in different aspects of Fd-linked metabolism, no conclusive evidence has been obtained for the biological significance ofthe isoproteins (4,7,19). Recently, the heterocyst of a blue-green alga, Anabaena variabilis, was shown to contain a specific Fd which is distinct from the Fd found in vegetative cells. The heterocyst Fd seemed to be involved in a specific interaction with nitrogenase (15).In the leaves of C4 plants, the metabolic process of photosynthesis is partitioned between two types of cell, BSC' and MC, and the intercellular compartmentalization ofthe assimilation of carbon and nitrogen is well documented (5). Furthermore, in the leaves of NADP-malic enzyme types of species, such as maize, almost all of capacity for non-cyclic electron flow is localized in the MC, and the PSII activity of the chloroplasts in the BSC is weak (5). In the course of a survey of Fd isoproteins in C4 plants, we Extraction and Partial Purification of FdDark-grown seedlings were divided into three parts, leaves including coleoptiles, mesocotyls and primary roots. Mesocotyl is the first internodal part formed above the seed storage tissues, which elongates considerably during growth in darkness. Ten g each of these tissues were ground with a mortar and pestle with 1 g of polyclar AT and a small amount of quartz sand in 40 ml of ice-cold extraction buffer (20 mM Tris-HCl (pH 7.5), 100 mm NaCl, 1 mM MgCl2, 1 mM EDTA, 1 mM PMSF, and 1%[v/v] 2-mercaptoethanol). The homogenate was filtered through two layers of cheese cloth and centrifuged at 12,000g for 10 min. The resulting supernatant was mixed with an excess amount of DEAE-cellulose (about 20 g wet weight) and the suspension of resin was packed in a column. After the column wa...

A Nitrate-Inducible Ferredoxin in Maize Roots (Genomic Organization and Differential Expression of Two Nonphotosynthetic Ferredoxin Isoproteins)

“…The supernatant containing Fd was passed through a small column of , and the absorbed Fd was eluted with elution buffer (50 mM Tris-HC1, pH 7.5, and 700 mM NaCl) in a small volume. The partially purified Fd fractions were analyzed by PAGE on a nondenaturing gel as described previously (Kimata and Hase, 1989). Proteins on gels were stained with Coomassie brilliant blue or electrotransferred to a PVDF membrane (Immobilon, Millipore) for western analysis (Towbin et al, 1979).…”

“…A number of groups have investigated the Fd and FNR in roots (Wada et al, 1986(Wada et al, , 1989Kimata and Hase, 1989;Hirasawa et al, 1990;Morigasaki et al, 1990;Green et al, 1991), and it has been demonstrated that the molecular species of the root enzymes are distinct from their counterparts in leaves. Most plants examined to date have multiple Fd isoproteins, which can be divided into two main groups.…”

“…Vol. 11 4,1997 predominantly in nonphotosynthetic organs such as roots and mature fruits (Wada et al, 1986;Kimata and Hase, 1989;Green et al, 1991;Alonso et al, 1995).…”

“…Most plants examined to date have multiple Fd isoproteins, which can be divided into two main groups. One group, referred to as photosynthetic Fd, is distributed only in leaves and the expression is stimulated by light (Elliott et al, 1989;Kimata and Hase, 1989;Vorst et al, 1990;Hase et al, 1991;Bovy et al, 1995). The other group, referred to as nonphotosynthetic Fd, is distributed Plant Physiol.…”

“…Fd I and Fd I1 belong to the group of photosynthetic Fds, whereas Fd 111 and Fd IV are of the nonphotosynthetic type (Kimata and Hase, 1989). Three cDNAs, pFD1, pFD3, and pFD5, have been isolated (Hase et al, 1991).…”