Changes in pigment levels, Rubisco and respiratory enzyme activity of Ficus benjamina during acclimation to low irradiance

Abstract

The objective of the present study was to determine the influence of reduced irradiance on the activities of ribulose bisphosphate carboxylase‐oxygenase (Rubisco) and respiratory enzymes. Rooted cuttings of the tropical epiphyte. Ficus benjamina L., were grown in a shaded environment that excluded approximately 50% of the natural photosynthetically active irradiance (890 μmol m−2 s−1) for 4 months. Established plants were transferred and grown for 10 months under a range of irradiance levels with daily average maxima varying from a full‐sun environment to 20% full sun (100%−1735; 50%−890; 40%−695; and 20%−303 μmol m−2s−1). Chlorophyll, carotenoid and soluble protein content increased in Ficus leaves as irradiance level decreased, while Rubisco increased on a fresh weight basis but decreased on a protein basis. Glycolytic enzymes, enolase and pyruvate kinase, showed higher activities in full‐sun plants on a protein and fresh weight basis. However, the activity of two mitochondrial enzymes, aconitase and malate dehydrogenase, was not different under the various irradiance levels. When transferred to a very low irradiance environment (18 μmol m−2 s−1), mature leaves exhibited increased chlorophyll and carotenoid levels regardless of previous irradiance treatment. Exposure to very low irradiance resulted in a large increase in enolase and pyruvate kinase activities. Only plants grown under full sun conditions showed a decline in Rubisco activity following growth at very low irradiance. Together, these studies demonstrate the ability of mature leaves of Ficus to biochemically adjust photosynthetic and respiratory components over a wide range of irradiance.