Indole-3-acetic Acid Catabolism by Soybean Bacteroids

Abstract

S U M M A R YBacteroid preparations from nodules of soybean were able to destroy aerobically substantial quantities of indole-3-acetic acid (IAA). Kinetic studies indicate the involvement of two processes. The supernatant derived during preparation of bacteroids had an active IAA oxidation during the first 30 min. Successive washings of bacteroids still retained some activity although it was reduced. A high level of IAA destruction was always observed with washed bacteriods and the reaction proceeded linearly for at least 4 h. Glucose gave a slight stimulation but succinate, pyruvate and fumarate at low concentrations (approx. 25 mM) were strong inhibitors. No IAA catabolism occurred with washed bacteroids at a POz of 30 mmHg or less, but it increasingly occurred with further increase in oxygen partial pressure up to 150 mmHg. No difference was observed between bacteroids with or without active nitrogenase. I N T R O D U C T I O NSignificant quantities of indole-3-acetic acid (IAA) occur in the nodules of different legumes (Pate, 1958 ;Dullaart, 1967). Mennes (1972) reported IAA degradation in nodules of Lupinus and suggested that bacteroids were not involved in this activity. Earlier results showed that different strains of free living Rhizobium could destroy IAA (Rigaud, 1969; Dullaart, 1970) and it was of interest to investigate the possible role of bacteroids in this catabolism. We report an IAA-oxidase activity in preparations of soybean bacteroids ; the effects of substrates and oxygen tensions were also investigated. M E T H O D SNodules. Soybeans (GlJicine inax Merr., cultivar Altona) inoculated with Rhizobiuin japonicutn cc705 (syn. Wisconsin 505), were grown in a glasshouse (temperature range 20 to 27 "C) in plastic pots in a 2:1 mixture of washed vermiculite and sand. The composition (g/l) of the culture medium was :

Functional characterization of the Bradyrhizobium japonicum modA and modB genes involved in molybdenum transport

“…10 8 cells per seed) of a single strain of B. japonicum. Plants were grown for 42 days in an N-free nutrient solution (Rigaud & Puppo, 1975), prepared by using MilliQ water and high-quality chemical products and supplemented or not supplemented with 0?8 mM molybdate. The sulphate concentration in the mineral solution used for plant growth was 3?5 or 10 mM.…”

Nitrogen and phosphorus availability limit N2 fixation in bean

“…phaseoli strain ISP-14 (1.27i 10* rhizobia ml −" ). Pots containing soil were watered with deionized water (soil treatments), while pots containing sand were irrigated with diluted (1\4) nutrient solution (Rigaud & Puppo, 1975). Three replicates per treatment were run.…”

The genus Micromonospora is widespread in legume root nodules: the example of Lupinus angustifolius

“…Seedlings were transferred to pots with sterile vermiculite and watered with nitrogen-free Rigaud and Puppo nutrient solution (Rigaud and Puppo, 1975). Fifteen plantelets (five per treatment) were inoculated with 1 ml each of a bacterial suspension (10 8 cells per ml) of strains Micromonospora Lupac 08 and Micromonospora Lupac 09T.…”