Infection by bact. radicicola in relation to the microchemistry of the host's cell walls

Abstract

Pt. I. Infection of root hairs. It is statistically proved that infection is not a mere invasion of mechanically injured or broken root hairs. Presence of bacteria, even of strains belonging to foreign inoculation-groups, causes significant increase in number of curled and bent hairs. The nodule bacteria invariably attack the tip of a root hair, a fact which may be related to some pre-existing physical difference at that point; they produce a secretion capable of modifying the wall, as evidenced by the abnormal curling of the tip. This secretion is separable from the cells by filtration and is not specific for plants of the cross-inoculation group to which the bacteria belong. The bacteria in culture could not be shown to attack cellulose, pectin or Ca pectate. Curled tips of root hairs, whether or not infected, contained the same constituents as normal hairs; these were cellulose, Ca pectate and probably pectose, and a very resistant hemicellulose.[long dash]Pt. II. Infection thread within the nodule. The cell walls of the nodule contain cellulose, a hemicellulose, Ca pectate in the mature parts, and pectose, at least in the meristematic tip. Walls of the tip also give a protein reaction. There are numerous pits perforating the secondary layers of the walls, but the middle lamellae appear to be continuous. These pits are of sufficient size to admit infection threads. The infection thread is surrounded by a definite sheath consisting of cellulose and hemicellulose; Ca pectate is absent and presence of other pectic materials was not confirmed. The sheath does not cross the middle lamella, and is probably a deposit of the individual plant cell. It is suggested that the bacterial zoogloea crosses a cell wall by way of the pits and is later covered by the sheath, a product of host cell activity.