C 4 photosynthesis and leaf anatomy in diploid and autotetraploid Pennisetum americanum (pearl millet)

Abstract

The effects of polyploidy on leaf anatomy and C 4 photosynthesis were studied in a diploid and a spontaneous autotetraploid of pearl millet ( Pennisetum americanum). Dimensions of photosynthetic cells, their numbers per unit leaf area, and numbers of chloroplasts per cell were determined. Photosynthesis was measured by leaf CO 2-exchange and activities of photosynthetic enzymes. There were exactly half as many photosynthetic cells per unit leaf area in tetraploids as in diploids. In tetraploid plants both mesophyll and bundle-sheath cells were 16 μM longer than in diploids. Changes in other dimensions resulted in a doubling of bundle-sheath cell volume, but only a 45% increase in mesophyll cell volume in tetraploids. There were twice as many chloroplasts per cell in the tetraploids, while the number of chloroplasts per unit leaf area was the same at both ploidy levels. The rate of CO 2 uptake was identical at the two ploidy levels on a leaf area basis, but was twice as high per cell in tetraploid plants. Changes due to polyploidy in contents of chlorophyll and leaf soluble protein, as well as enzyme activities per cell and on a leaf area basis corresponded to changes in photosynthetic rates. The differences in the photosynthetic capacity of this polyploid C 4 plant and those of a previously studied, established and naturally-occuring polyploid C 4 grass ( Panicum virgatum) are discussed.