Abstract
Species differences in photosynthetic CO2 uptake by isolated protoplasts from citrus leaves were investigated in comparison with the net photosynthetic rate (Pn) per unit leaf area of attached leaves.
Among 14 species, Natsudaidai (Citrus natsudaidai Hayata) and Pummelo (C. grandis Osbeck) showed the highest Pn, at about 19mg CO2/dm2• h. On the contrary satsuma mandarin (C. unshiu Marc.), Yuzu (C. junos Sieb. ex Tanaka), and Ponkan (C. reticulata Blanco) had the lowest Pn at 12-14mg CO2/dm2 Generally, these species could be divided into three groups. The higher Pn was shown by Archicitrus, the lower by Metacitrus, and hybrids such as Kiyomi tangor (C. unshiu Marc.×C. sinensis Osbeck) and Minneola tangelo (C. paradisi×C. tangerine) exhibited intermediate values. Diversification of photosynthesis by attached leaves was mainly the result of differences in specific leaf weight, chlorophyll content, stomatal density, and enzyme activity.
There were some differences in photosynthesis between protoplasts and leaves, although the results of investigations with isolated protoplasts were similar to those of attached leaves. Natsudaidai and Pummelo showed relatively low Pn of protoplasts in spite of the higher Pn by leaves. These phenomena suggested the possibility of enhancement of Pn in leaves through improvement of leaf structure.
