Aggregative movement of C₄ mesophyll chloroplasts is promoted by low CO₂ under high intensity blue light

Abstract

C4 plants supply concentrated CO2 to bundle sheath (BS) cells, improving photosynthetic efficiency by suppressing photorespiration. Mesophyll chloroplasts in C4 plants are redistributed toward the sides of the BS cells (aggregative movement) in response to environmental stresses under light. Although this chloroplast movement is common in C4 plants, the significance and mechanisms underlying the aggregative movement remain unknown. Under environmental stresses, such as drought and salt, CO2 uptake from the atmosphere is suppressed by closing stomata to prevent water loss. We hypothesized that CO2 limitation may induce the chloroplast aggregative movement. In this study, the mesophyll chloroplast arrangement in a leaf of finger millet, an NAD‐malic enzyme type C4 plant, was examined under different CO2 concentrations and light conditions. CO2 limitation around the leaves promoted the aggregative movement, but the aggregative movement was not suppressed, even at the higher CO2 concentration than in the atmosphere, under high intensity blue light. In addition, mesophyll chloroplasts did not change their arrangement under darkness or red light. From these results, it can be concluded that CO2 limitation is not a direct inducer of the aggregative movement but would be a promoting factor of the movement under high intensity blue light.

CO2‐induced chloroplast movement in one cell‐layer moss leaves

“…CO 2 leakage from the bundle sheath would increase under such stress conditions (Ubierna et al, 2013), which supports the hypothesis that this chloroplast aggregation is the result of positive CO 2 ‐tactic movement. Indeed, this chloroplast aggregation was reported to be enhanced at low ambient CO 2 concentration (Kato et al, 2023). However, neither the epistrophe arrangement of chloroplasts nor the chloroplast aggregation in C4 plants has been confirmed to be directly induced by CO 2 .…”

Salicylic Acid and Water Stress: Effects on Morphophysiology and Essential Oil Profile of Eryngium foetidum

“…Plants can induce defense mechanisms, such as stomatal closure and osmotic adjustment, to prevent the harmful effects of water stress [6,7]. Under drought stress, plants close their stomata to prevent water loss, which consequently reduces CO 2 uptake, directly affecting the photosynthetic rate [8]. This impairment in gas exchanges induces changes in leaf metabolism, inhibiting photosynthesis [4,7,9].…”