Nitrogenase Activity Associated with Roots and Stems of Field-Grown Corn (Zea mays L.) Plants

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Abstract
Corn (Z. mays L.) plants were assayed for nitrogenase activity (C2H2 reduction) during early ear development. Hybrid corn and inbred lines were grown separately at 2 experimental fields in New Jersey [USA]. Acetylene-dependent ethylene production was observed a few hours after harvest, from the field, on intact plants, root-soil cores, lower stem segments and excised roots, all assayed under air and not preincubated previously. Incubation of excised roots at 1% O2 resulted in lower rates of C2H2 reduction. The time course of C2H2 reduction by excised roots, assayed in air, was similar for all genotypes studied (2-hybrids, 8 inbreds and a cross of corn .times. teosinte) and indicated that a long preincubation at reduced O2 is not absolutely required for early detection of nitrogenase activity. Isolation of N2-fixing bacteria from within the roots and stems, with the diurnal fluctuation of nitrogenase activity in response to day/night cycles, were indicative of a close association with plant function. Evidently, the nitrogenase activity associated with corn plants growing in a temperate climate is dependent upon indigenous N2-fixing bacteria.