Photosynthetic response to varying light intensity in ecotypes of Solanum dulcamara L. from shaded and exposed habitats.

Within the widespread species Solanum dulcamara, contrasting ecotypes were found which are physiologically adapted to the light intensities prevailing in their natural habitats. When grown under a high light intensity, an ecotype from a shaded habitat exhibits signs of damage. Another one from an exposed habitat has higher rates of photosynthetic CO2 uptake when grown under strong as compared to weak light and does not show damage. This differential response becomes even more evident when leaves of both ecotypes are grown to maturity under weak light and are subsequently subjected to strong light for some time. The quantum requirement for photosynthesis increases in the shade-, but not in the sun-ecotype. The sun type increases its rate of photosynthesis under saturating light intensities after a few days in strong light.No significant difference in physical resistances to gas diffusion could be found to explain the highly differing rates of photosynthesis. With the increase in photosynthetic capacity in leaves of the sun type, protein content, activity of RuDP carboxylase, and concentration of Fraction I protein increased likewise. It is suggested that de novo synthesis of photosynthetic enzymes in fully expanded leaves of the sun ecotype following treatment with strong light is the cause of its increased capacity for CO2 fixation.