Hypergravity of 10g Changes Plant Growth, Anatomy, Chloroplast Size, and Photosynthesis in the Moss Physcomitrella patens
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The photosynthetic and anatomical responses of bryophytes to changes in gravity will provide crucial information for estimating how these plant traits evolved to adapt to changes in gravity in land plant history. We performed long-term hypergravity experiments at 10g for 4 and 8 weeks using the moss Physcomitrella patens with two centrifuges equipped with lighting systems that enable long-term plant growth under hypergravity with irradiance. The aims of this study are (1) to quantify changes in the anatomy and morphology of P. patens, and (2) to analyze the post-effects of hypergravity on photosynthesis by P. patens in relation to these changes. We measured photosynthesis by P. patens for a population of gametophores (e.g., canopy) in Petri dishes and plant culture boxes. Gametophore numbers increased by 9% for a canopy of P. patens, with 24–27% increases in chloroplast sizes (diameter and thickness) in leaf cells. In a canopy of P. patens, the area-based photosynthesis rate (A canopy) was increased by 57% at 10g. The increase observed in A canopy was associated with greater plant numbers and chloroplast sizes, both of which involved enhanced CO2 diffusion from the atmosphere to chloroplasts in the canopies of P. patens. These results suggest that changes in gravity are important environmental stimuli to induce changes in plant growth and photosynthesis by P. patens, in which an alteration in chloroplast size is one of the key traits. We are now planning an ISS experiment to investigate the responses of P. patens to microgravity.
KeywordsBryophyte Leaf CO2 diffusion Evolution Gametophore
This work was supported by a Grant-in-Aid for Space Utilization by the Japan Aerospace Exploration Agency (to T.F. in Space Moss Project) and JSPS KAKENHI Grant Numbers JP21657011 and 15K11914. We appreciate Dr. Yosuke Onoda for his constructive comments concerning the effects of leaf anatomy on photosynthesis.
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