Effects of chloroplast dysfunction in a subpopulation of leaf mesophyll cells on photosynthetic and respiratory activities of a whole leaf: A study using variegated leaves of Hedera helix L.

Abstract

A variegated leaf of Hedera helix is composed of green and white mesophyll cells with and without photosynthetic capacity, respectively. We measured the photosynthesis and dark respiration rates, as well as CO2 compensation points, of H. helix leaves with various extents of variegation. The photosynthetic rate (on an area basis) of the variegated leaves increased almost linearly according to the increase in the proportion of green area to total leaf area. In contrast, dark respiration rate was nearly constant irrespective of the extent of leaf variegation. These results suggest that chloroplast dysfunction in white mesophyll cells did not drastically affect photosynthetic activity of green mesophyll cells, or respiratory rates of both green and white mesophyll cells. CO2 compensation point was elevated when the proportion of green area became extremely low, indicating that the proportion of non-photosynthetic cells within a photosynthetic organ could affect its CO2 compensation point.