NITROGEN DEFICIENCY EXACERBATES THE EFFECTS OF LIGHT STRESS IN PHOTOAUTOTROPHIC SUSPENSION-CULTURED CELLS OF CHENOPODIUM-RUBRUM

Nitrogen deficiency caused pronounced reductions in the photosynthetic capacity and differential losses in chlorophyll, cytochrome f and Mg2 +-specific ATPase amounts or activities in suspension cultured cells o f Chenopodium rubrum L. This reduced outfit of the photosynthetic mach inery and limited protein turnover capacity are possible reasons for o ur observation that nitrogen deficiency exacerbates the harmful effect s of high irradiance on photosystem 2 photochemical efficiency. The ef fect of nitrogen deficiency on photoinhibition increased over a broad range of photon flux densities and it was detectable in both the short -term and long-term experiments. Differences in the effects of the nit rogen regime and irradiance on several growth parameters were demonstr ated. The main effect of nitrogen deficiency was a reduction of protei n synthesis and cell division, whereas the irradiance chiefly affected the accumulation of carbon in the cell suspensions. Synergistic effec ts of nitrogen regime and irradiance could also be demonstrated for be talain accumulation which was the greatest under high irradiance and e xpressed nitrogen deficiency.