NADH Nitrate Reductase and NAD(P)H Nitrate Reductase in Genetic Variants and Regenerating Callus of Maize

Abstract

ABSTRACI?Different organs of maize seedlings are known to contain different complements of NADH and NAD(P)H nitrate reductase (NR) activity.The study of the genetic programming that gives rise to such differences can be initiated by looking for genetic variants exhibiting different patterns of distribution of the above enzymes. We demonstrate in this work that scutella of very young maize seedlings contain NADH NR almost exclusively and that this activity is gradually replaced, as the seedling ages, with NAD(P)H NR. Leaves in the seedlings contain exclusively the NADH NR activity. A genetic variant is described that contains much reduced levels of NAD(P)H NR activity but not of NADH NR activity in the scutellum. This same variant exhibits a relatively low level of NAD(P)H NR but normal NADH NR activity in seedling root tips. These observations suggest that the genetic program used to specify the scutellar complement of NR activity shares some common components with the genetic program used to determine the young root tip complement of NR activities. Parts of regenerating callus at different stages of differentiation were examined to determine when the differences in NR complement begin to appear. The same pattern of NADH NR and NAD(P)H NR activities was found in unorganized as well as in organized callus, in recognizable root-like and even in green shoot-like material, both activities being present in all these tissues. An examination of the NR complement in different organs of a number of siblings originating from a cross involving transposon Mu-containing parents and having different levels of leaf NADH NR activity shows that the leaf NADH NR activity content and the scutellum NAD(P)H NR activity content are relatively independent of each other, indicating that the genetic programs specifying the NR content of these organs are not tightly coupled, if at all.(1) found that scutella contained both NADH and NAD(P)H activities, the latter using NADPH preferentially as electron donor, whereas leaves had no NAD(P)H NR activity. Redinbaugh and Campbell (7) examined young maize roots and found both NADH and NAD(P)H NR activities. On the basis of similarities in electron donor specificity, pH optimum, Stoke's radius, and Km for nitrate, these investigators concluded that the root NADH activity was identical with the leaf activity. Comparisons with NR activities in the scutellum were incomplete and revealed differences that were hard to interpret.Wells and Hageman (12) pointed out that phosphatases can complicate studies on the pyridine nucleotide specificity of NR because they can catalyze the conversion of NADPH to NADH. When studying NADH and NAD(P)H NR it is therefore necessary either to separate the enzymes physically, purify them away from contaminating phosphatases, inactivate the phosphatases, or continuously eliminate NADH from a NADPH dependent assay, in order to interpret the results in terms of the NADH or the NAD(P)H specific enzyme activity.In this study we show that scutella in very young maize seedlings ...

InVitro Biochemical studies on certain mulberry verities of M5, V1, S36 and Anantha.

“…as it was also suggested by many others earlier (George Sorger et al, 1986; Altaf Ahmed and Abdin, 1999) and the results of the present study are in accordance with the results reported earlier in mustard seedlings by Altaf and Abdin (1999), as it was explained that, whenever the nitrate concentration is more than 20mM, it is reduced to nitrite by NAD(P)H : NR as this isoform dominantly active than the other isoforms at nitrate concentrations above 20mM and can utilize either NAD(P)H alone or the combination of NADH : NAD(P)H as the coenzymes, whereas the other isoform can utilize NADH efficiently than NAD(P)H, optimally functions at low nitrate concentration (<10 mM). Hence, it could be concluded here that at 30 mM concentrations of nitrate and until day '15' to the day '20' the nitrate reduction was carried out by NAD (P) H: NR and thereafter with the decreased levels (low levels) of nitrate the isoform activity was gradually declined and NADH: NR was observed to be active at low levels of medium nitrogen.…”

Nitrate metabolism in roots and nodules of Vicia faba in response to exogenous nitrate

“…Three apparently genetically different forms of NRs have been described for soybean leaves (Campbell and Smarelli 1986, Streit and Harper 1986, Sorger et al 1986. Vicia faba has been reported as only containing NADH-HR (Hewitt and Notton 1980).…”

Genotypic Responses of Vegetable Crops to Nitrogen Nutrition

“…Nitrate reduction is a genetically controlled factor in the assim ilation of N (Table 4). Higher plants generally have more than one kind of nitrate reductase (Guerrero et al, 1981;Sorger et al, 1986). The enzyme may be constitutive or inducible by substrate (Heath-Pagliuso et al, 1984;Nelson et al, 1986;Streit et al, 1985).…”

“…Isozymes of nitrate reductase may be distributed in various plant organs and may change during plant development (Sorger et al, 1986). Nitrate reductase activity in plants and its distribution among various organs are under genetic control (Cove, 1979;Fortini et al, 1975;Gallagher et al, 1980;Rao et al, 1977;Sorger et al, 1986;Warner et al, 1969).…”

“…Isozymes of nitrate reductase may be distributed in various plant organs and may change during plant development (Sorger et al, 1986). Nitrate reductase activity in plants and its distribution among various organs are under genetic control (Cove, 1979;Fortini et al, 1975;Gallagher et al, 1980;Rao et al, 1977;Sorger et al, 1986;Warner et al, 1969). It is not clear whether the genetic effects are on specific isozymes of nitrate reductase or on factors that affect synthesis and degradation of the enzyme, endogenous inhibitors or activators, or affinity of the enzyme for substrate.…”