Campbell, WH; Ziegler, P; Beck, E: Development of nitrogen assimilation enzymes during photoautotrophic growth of Chenopodium-rubrum suspension-cultures, Plant Physiology, 74, 947-950 (1984), doi:10.1104/pp.74.4.947 | |
Abstract: Chenopodium rubrum cells were grown in suspension as a photoautotrophic culture with a 16 hour day. Cell growth had three phases: a 3-day lag, a 3-week logarithmic phase, and a 10-day stationary phase. Chlorophyll content increased steadily during log phase and reached a level of 0.5 to 0.6 mg Chl g−1 fresh weight. Soluble protein of the cells increased more rapidly from day 4 to day 12 than during midlog phase. Initially, ammonium was taken up in preference to nitrate. However, during the second two weeks of growth, ammonium and nitrate were taken up simultaneously; this period of growth was the time of highest rates of N uptake by the cultured cells. Glutamine synthetase had a high specific activity (17 μmol·hour−1 mg−1 protein) in day 1 cells, and this level was sustained until midlog phase when it increased by 20%. Methyl viologen-dependent glutamate synthase specific activity increased rapidly in lag phase cells (day 4 = 10 μmol·hour−1 mg−1 protein), but decreased by day 9 to about 50% of the peak and remained constant. NADH:nitrate reductase specific activity increased rapidly in lag phase cells and reached a plateau that lasted from day 4 to 14 (1 μmol·hour−1 mg−1 protein). Methyl viologen-dependent nitrite reductase specific activity was high when assayed on day 5 and increased to a maximum on day 15 to 16 (12 μmol·hour−1 mg−1 protein). NADPH- and NADH-dependent glutamate dehydrogenase specific activities remained rather constant throughout the growth cycle. The cells appeared to have developed photosynthetic competence and to have leaf-like activities of nitrogen assimilation enzymes. |