Growth, ageing and death of a photoautotrophic plant cell culture

Batch cultures of photoautotrophic cell suspensions of Chenopodium rubrum L .. growing in an inorganic medium on CO2 under a daily balanced light-dark regime of 16:8h could be maintained for approximately 100 d without subcult ivation. The long-lived cultures showed an initial cell division phase of 4 weeks, followed by a stationary phase of another 4 weeks. after which agei ng and progressive cell death reduced the number of living cells and the cu ltures usually expired after another 3-4 weeks. These developmental phases of the cell culture were characterised with respect to photosynthetic perfo rmance. dark respiration. content of phytohormones and capacity of cell div ision. Cell division of the majority of the cells finished in the G1- or G0 -phase of the cell cycle, caused by a pronounced decline in the endogenous levels of auxin and cytokinins. Supply of these growth factors to resting c ells resulted in resumption of cytokinesis, at least by some of the cells. However. responsiveness to the phytohomones declined during the stationary phase. and subcultivation was no longer possible beyond day 60 when the pha ses of ageing and death commenced. Ageing was characterised by a further de cline in the photosynthetic capacity of the cells, by a climacteric enhance ment of dark respiration. but also by a slight increase in the level of IAA and cytokinins concomitant with a decrease in ethylene. Similarities and d ifferences between the development of batch-cultured photoautotrophic cells of C. rubrum and that of a leaf are discussed with respect to using the ce ll culture as a model for a leaf.