Physiological studies on N₂-fixing root nodules of Datisca cannabina L. and Alnus nitida Endl. from Himalaya region in Pakistan

The nodulation and the morphology and physiology of the nodules were studied on Datisca cannabina, a perennial herb from northern Pakistan and Alnus nitida, a nodulated tree in the same locality. Both species bear coralloid clusters of actinorhizal nodules. The main free amino acid in D. cannabina nodules was arginine while the predominant free amino acid in A. nitida nodules was citrulline. The infectivity of crushed nodules of both types of plants on their respective host was about 10₆ infective particles per gram of nodule fresh wt. In cross-inoculation experiments crushed nodule inoculum from A. nitida failed to induce nodulation on D. cannabina seedlings but the crushed nodule inoculum from D, cannabina caused low nodulation on seedlings of A. nitida (10³ infective particles. g nodule fresh wt.). The activity of nitrogenase, hydrogenase and respiration (O₂ uptake) were measured in detached nodules, nodule homogenates and the 20 µm residue and 20 µm filtrate preparations from the nodules of both species. Both species showed similar patterns of activities except that only the nodule homogenate and 20 µm residue preparations from D. cannabina showed pronounced enhancement of the O₂ uptake by succinate which was further stimulated by ADP. This has in part been explained by the presence of mitochondria in close connection with the endophyte.