Premium
O 2 regulation and O 2 ‐limitation of nitrogenase activity in root nodules of pea and lupin
Author(s) -
Castillo Leonor Diaz del,
Hunt Stephen,
Layzell David B.
Publication year - 1992
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.1992.860212.x
Subject(s) - nitrogenase , rhizosphere , lupinus , pisum , biology , root nodule , sativum , leghemoglobin , respiration , botany , nitrogen fixation , shoot , horticulture , bacteria , genetics
The gas exchange characteristics of intact attached nodulated roots of pea ( Pisum sativum cv. Finale X) and lupin ( Lupinus albus cv. Ultra) were studied under a number of environmental conditions to determine whether or not the nodules regulate resistance to oxygen diffusion. Nitrogenase activity (H 2 evolution) in both species was inhibited by an increase in rhizosphere pO 2 from 20% to 30%, but recovered within 30 min without a significant increase in nodulated root respiration (CO 2 evolution). These data suggest that the nodules possess a variable barrier to O 2 diffusion. Also, nitrogenase activity in both species declined when the roots were either exposed to an atmosphere of Ar:O 2 or when the shoots of the plants were excised. These declines could be reversed by elevating rhizosphere pO 2 , indicating that the inhibition of nitrogenase activity resulted from an increase in gas diffusion resistance and consequent O 2 ‐limitation of nitrogenase‐linked respiration. These results indicate that nodules of pea and lupin regulate their internal O 2 concentration in a manner similar to nodules of soybean, despite the distinct morphological and biochemical differences that exist between the nodules of the 3 species. Experiments in which total nitrogenase activity (TNA = H 2 production in Ar:O 2 ) in pea and lupin nodules was monitored while rhizosphere pO 2 was increased gradually to 100%, showed that the resistance of the nodules to O 2 diffusion maintains nitrogenase activity at about 80% of its potential activity (PNA) under normal atmospheric conditions. The O 2 ‐limitation coefficient of nitrogenase (OLC N = TNA/PNA) declined significantly with prolonged exposure to Ar:O 2 or with shoot excision. Together, these results indicate a significant degree of O 2 ‐limitation of nitrogenase activity in pea and lupin nodules, and that yields may be increased by realizing full potential activity.