| Abstract: | The addition of choline chloride (1 mM ) to the rooting medium of Zea mays seedlings as well as enhancing salt tolerance, caused the pH of the medium to drop rapidly by 1.5 to 2.0 pH units in 24 h. This compares with a drop of 0.2 to 0.3 pH units in the presence of NH4+ under equivalent conditions. In pot experiments choline treatment promoted the growth of maize and other species under alkaline conditions more effectively than NH4+. The acidification of the root medium was due to choline catabolism by bacteria, characterised as a strain of Pseudomonas fluorescens, introduced into the medium by the seedling roots. Choline is probably metabolised by the organism via betaine aldehyde and betaine to sarcosine. The acidification step is associated with the oxidation of betaine aldehyde to betaine. The possible role of rhizosphere pH changes and the modification of plant metabolism by chemicals found in the soil are discussed in relation to plant growth under natural conditions. |
