Photoautotrophic potato cells: Transition from heterotrophic to autotrophic growth

Abstract

Cells of potato (Solanum tuberosum L.) were obtained which were capable of photoautotrophic growth in liquid suspension culture under a photon flux density of 90–110 μmol m−2 s−1 PAR and in an atmosphere enriched with 2% CO2. These photoautotrophic cells contained between 100 to 200 μg Chl (g fresh weight)−1 and fixed CO2 at a maximum rate of 16 μmol CO2 (g fresh weight)−1h−1. In order to obtain cells capable of photoautotrophic growth it was necessary to adapt highly chlorophyllous heterotrophic cells (>50 μg Chl (g fresh weight)−1) for growth in medium with 2.5 g sucrose 1−1 (photomixotrophic cells). The photomixotropic cells had a Chl content of ca 100 μg Chl (g fresh weight)−1 and were capable of photosynthetic activity which allowed them to survive after sugars had been depleted from the medium. It was from the photomixotrophic cells that cells capable of photoautotrophic growth were obtained.Heterotrophic cells initially established in liquid medium with 25 g sucrose I−1 from chlorophyllous callus contained about 50 to 150 μg Chl (g fresh weight)−1. However, after 5 to 10 passages the Chl content decreased to a maximum of 15 μg Chl (g fresh weight)−1. These cells could not be adapted to photomixotrophic or photoautotrophic growth. These cells also were not able to regain Chl or initiate high rates of CO2 fixation during the stationary phase of growth as did photomixotrophic cells or chlorophyllous heterotrophic cells. The loss of Chl exhibited by the cells during adaption to heterotrophic growth could be attributed at least in part to unbalanced growth (when cell division and growth exceeds Chl accumulation). Sucrose appeared to have an inhibitory effect directly on photosynthesis independent of Chl accumulation.