IMPROVEMENT OF PHOTOAUTOTROPHIC SOLANUM TUBEROSUM PLANTLET CULTURE BY LIGHT AND CO₂ : DIFFERENTIAL DEVELOPMENT OF PHOTOSYNTHETIC CHARACTERISTICS AND VARIETAL CONSTRAINTS.

Both light (350 vs 80 μmol photons m^-2 s^-1) and CO₂ (20000 vs 340 μL.L^-1 CO₂) stimulated growth of photoautotrophic cultures of Solanum tuberosum cv. Haig. CO₂ enrichment had the strongest effect on fresh weight increase. Light stimulation of photosynthetic oxygen exchange was greater in plantlets grown in high light than in plantlets grown in low light. Cultivation in high light also stimulated protein content and Rubisco activity. In order to test if CO₂ and light stimulation of photoautotrophic growth could be generalized, the behaviour of 28 cultivars of Solanum tuberosum has been studied. Eight cultivars bleached and died rapidly, six survived but grew slowly and fourteen grew well. Among the growing cultivars, three groups were distinguished. Growth response of plantlets was correlated to the development of photosynthetic carbon metabolism. The high light regime, stimulating growth of some cultivars (e.g. cv. Haig), was a stressor for some others.