Effects of CO2 and sugars on photosynthesis and composition of avocado leaves grown in vitro

The effects of micropropagation conditions on avocado (Persea americana Mill.) have been measured in leaves and plants cultured in vitro. The consequences of the type and concentration of sugar in the medium and of carbon dioxide concentration in the atmosphere on the rates of photosynthesis and amounts of ribulose 1,5-biphosphate carboxylase-oxygenase (EC 4.1.1.39; Rubisco) and total soluble protein (TSP) were measured. At the highest sucrose supply (87.6 mM), Rubisco content was substantially decreased in leaves, and even more when elevated CO2 (1 000 μmol·mol−1) was supplied. Maximum photosynthetic rate (Pmax) was significantly decreased when plants developed in high sucrose and elevated CO2. However, Rubisco concentration was significantly greater when glucose was supplied at the same molar concentration or when the concentration of sucrose was small (14.6 mM), and no differences were observed due to the CO2 concentration in the air in these treatments. The ratio of Rubisco to total soluble protein (Rubisco/TSP) was dramatically decreased in plants grown in the highest concentration of sucrose and with elevated CO2. Leaf area and ratio of leaf fresh weight/(stem + root) fresh weight, were greater in plants grown with CO2 enriched air. However, upon transplanting, survival was poorer in plants grown on low sucrose/high CO2 compared to those grown on high sucrose/high CO2.