Abstract
ABSTRACT Mesophyll (M) chloroplasts in finger millet are known to aggregate to the bundle sheath side when leaves are constantly irradiated with extremely high-intensity light. This aggregative movement of M chloroplasts is also observed in natural environment, but whether a natural light regime is effective in inducing the response remains unclear. Abscisic acid is reported to trigger not only the aggregative movement but also stomatal closure, but photosynthetic responses accompanying the aggregative movement also remain unknown.We investigated changes in chloroplast positioning and photosynthetic traits under diurnal patterns of light, mimicking the natural light environment. M chloroplasts showed the aggregative movement with increasing light intensity whether it frequently fluctuated or not, and kept their aggregative positions in the midday. With decreasing light intensity, M chloroplasts returned to the random position in the evening. These results suggest that M chloroplasts often rearrange their intracellular positions during the daytime and that the chloroplast aggregative movement can be induced by a natural regime of light. The chloroplast aggregative movement was observed with increasing stomatal conductance, suggesting that stomatal closure is not crucial to trigger the chloroplast response.
Highlights
In many plants, the intracellular location of chloroplasts is regulated by light intensity and quality (Haupt, 1973; Inoue & Shibata, 1974; Trojan & Gabryś, 1996; Wada et al., 2003)
Effect of a natural regime of light on the chloroplast aggregative movement To clarify the involvement of a natural regime of light in triggering the aggregative movement of M chloroplasts under well-watered conditions, we investigated changes in chloroplast positioning during two different natural light regimes with frequent or less fluctuations of light intensity (Figure 1)
Chloroplast movement is analyzed by measuring changes in leaf transmittance or absorbance (Wada et al, 2003)
Summary
The intracellular location of chloroplasts is regulated by light intensity and quality (Haupt, 1973; Inoue & Shibata, 1974; Trojan & Gabryś, 1996; Wada et al., 2003). Chloroplast photorelocation movement has been well-studied and characterized in a C3 plant, Arabidopsis
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