AUTHOR=Cun Zhu , Xu Xiang-Zeng , Zhang Jin-Yan , Shuang Sheng-Pu , Wu Hong-Min , An Tong-Xin , Chen Jun-Wen 

TITLE=Responses of photosystem to long-term light stress in a typically shade-tolerant species Panax notoginseng

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1095726

DOI=10.3389/fpls.2022.1095726

ISSN=1664-462X

ABSTRACT=<p>Photosynthetic adaptive strategies vary with the growth irradiance. The potential photosynthetic adaptive strategies of shade-tolerant species <italic>Panax notoginseng</italic> (Burkill) F. H. Chen to long-term high light and low light remains unclear. Photosynthetic performance, photosynthesis-related pigments, leaves anatomical characteristics and antioxidant enzyme activities were comparatively determined in <italic>P. notoginseng</italic> grown under different light regimes. The thickness of the upper epidermis, palisade tissue, and lower epidermis were declined with increasing growth irradiance. Low-light-grown leaves were declined in transpiration rate (Tr) and stomatal conductance (Cond), but intercellular CO<sub>2</sub> concentration (<italic>C</italic><sub>i</sub>) and net photosynthesis rate (<italic>P</italic><sub>n</sub>) had opposite trends. The maximum photo-oxidation <inline-formula><mml:math display="inline" id="im1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mtext>P</mml:mtext><mml:mn>700</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:math></inline-formula> (<italic>P</italic><sub>m</sub>) was greatly reduced in 29.8% full sunlight (FL) plants; The maximum quantum yield of photosystem II (<italic>F</italic><sub>v</sub>/<italic>F</italic><sub>m</sub>) in 0.2% FL plants was significantly lowest. Electron transport, thermal dissipation, and the effective quantum yield of PSI [Y(I)] and PSII [Y(II)] were declined in low-light-grown plants compared with high-light-grown <italic>P. notoginseng</italic>. The minimum value of non-regulated energy dissipation of PSII [Y(NO)] was recorded in 0.2% FL <italic>P. notoginseng</italic>. OJIP kinetic curve showed that relative variable fluorescence at J-phase (<italic>V</italic><sub>J</sub>) and the ratio of variable fluorescent <italic>F</italic><sub>K</sub> occupying the <italic>F</italic><sub>J</sub>-<italic>F</italic><sub>O</sub> amplitude (<italic>W</italic><sub>k</sub>) were significantly increased in 0.2% FL plants. However, the increase in <italic>W</italic><sub>k</sub> was lower than the increase in <italic>V</italic><sub>J</sub>. In conclusion, PSI photoinhibition is the underlying sensitivity of the typically shade-tolerant species <italic>P. notoginseng</italic> to high light, and the photodamage to PSII acceptor side might cause the typically shade-tolerant plants to be unsuitable for long-term low light stress.</p>