Host factors influencing infection and nodule development in leguminous plants

Dr Thornton has shown that much of the diversity in the symbiosis between the leguminous plant and root-nodule bacteria can be attributed to inherent bacterial strain differences which show themselves, however, only in the symbiosis and are not causally related to any known in vitro property of the bacteria. On the plant side also very little of significance has been discovered connecting the physiology or metabolism of the host with symbiotic behaviour. As a result mainly of studies of environmental effects, it has been established that in general any factor which increases the proportion of available carbohydrate in the host’s tissues at the expense of the nitrogen content tends to be associated with an increase in nitrogen fixation (Fred & Wilson 1934; Wilson 1940, and others). On the other hand, factors decreasing the C/N ratio tend to reduce nodule size, and in extreme cases may so change the behaviour of the bacteria within the nodule as to result in tissue disintegration (Brenchley & Thornton 1925; Thornton 1930). This relation is not sufficiently well characterized to throw much light on the nodulation process, nor can it do so until the qualitative differences in the carbon and nitrogen fractions have been established.
RESP-3064