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

Abstract

Photosynthetic adaptive strategies vary with the growth irradiance. The potential photosynthetic adaptive strategies of shade-tolerant species Panax notoginseng (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 P. notoginseng 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 CO2 concentration (Ci) and net photosynthesis rate (Pn) had opposite trends. The maximum photo-oxidation P700+ (Pm) was greatly reduced in 29.8% full sunlight (FL) plants; The maximum quantum yield of photosystem II (Fv/Fm) 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 P. notoginseng. The minimum value of non-regulated energy dissipation of PSII [Y(NO)] was recorded in 0.2% FL P. notoginseng. OJIP kinetic curve showed that relative variable fluorescence at J-phase (VJ) and the ratio of variable fluorescent FK occupying the FJ-FO amplitude (Wk) were significantly increased in 0.2% FL plants. However, the increase in Wk was lower than the increase in VJ. In conclusion, PSI photoinhibition is the underlying sensitivity of the typically shade-tolerant species P. notoginseng 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.

Terrestrial and Floating Aquatic Plants Differ in Acclimation to Light Environment

“…Use of these remotely sensed, non-destructive fluorescence parameters allowed monitoring of these changing relationships from the same leaf throughout the day. The ability of plants to respond to differences in light environment is based on corresponding acclimatory up- and down-regulation of the capacities for photosynthesis, foliar export of [ 3 , 17 ], and photoprotective processes [ 3 , 18 , 19 , 20 ], resulting in a coordinated acclimation to the light environment of plant function, anatomy, and morphology (for a review, see [ 21 ]).…”

“…Use of these remotely sensed, non-destructive fluorescence parameters allowed monitoring of these changing relationships from the same leaf throughout the day. The ability of plants to respond to differences in light environment is based on corresponding acclimatory up-and down-regulation of the capacities for photosynthesis, foliar export of [3,17], and photoprotective processes [3,[18][19][20], resulting in a coordinated acclimation to the light environment of plant function, anatomy, and morphology (for a review, see [21]). , (c,d) the estimated rate of photosynthetic electron transport (green symbols and shading; incident photons × [F m ' − F]/F m '; same data as shown in panels (a,c) for the sun-exposed leaf), and (e,f) the level of non-photochemical fluorescence quenching (orange symbols and shading) as another estimate of the non-photochemical route (thermal dissipation of excess excitation energy) in leaves of the evergreen groundcover Vinca major.…”