Summary: Darkness and treatment with combined nitrogen (NH4Cl or KNO3) were used to induce nodule senescence in alfalfa and soybeans. Nodule senescence was assessed by determinations of the acetylene-reducing activity and leghaemoglobin and sugar contents of the nodules. Bacteroids from nodules of the treated plants were compared using flow microfluorimetry. Upon induced nodule senescence, alfalfa bacteroids decreased both in nucleic acid content and cell size while the soybean bacteroids were essentially unaffected.
Summary: The influence of specific growth rate on the ammonia-assimilating enzymes glutamine synthetase, NADP-linked glutamate synthase and NADP-linked glutamate dehydrogenase was studied in ammonia-limited and glucose-limited chemostat cultures of Erwinia carotovora var. carotovora, E. nigrifluens and E. amylovora. The response of these organisms, representatives of various ‘enzyme groups’ within the genus Erwinia, showed considerable variation and confirmed the heterogeneity of the genus with respect to ammonia-assimilating enzymes. The overall significance of the glutamine synthetase/glutamate synthase pathway in any organism where the synthesis of these enzymes is not constitutive is questioned.
Summary: A mathematical model for hyphal growth and branching is described which relates cytological events within hyphae to mycelial growth kinetics. Essentially the model quantifies qualitative theories of hyphal growth in which it is proposed that vesicles containing wall precursors and/or enzymes required for wall synthesis are generated at a constant rate throughout a mycelium and travel to the tips of hyphae where they fuse with the plasma membrane, liberating their contents into the wall and increasing the surface area of the hypha to give elongation. The hypothesis that there% a duplication cycle in hyphae which is equivalent to the cell cycle observed in unicellular micro-organisms is also included in the model. Predictions from the model are compared with experimentally observed growth kinetics of mycelia of Geotrichum candidurn and Aspergillus nidulans. The finite difference model which was constructed is capable of predicting changes in hyphd length and in the number and positions of branches and septa on the basis of changes in vesicle and nuclear concentration. Predictions were obtained using the model which were in good agreement with experimentally observed data.