Photodamage to photosystem in a typically shade-tolerant species Panax notoginseng exposed to a sudden increase in light intensity

doi:10.17521/cjpe.2021.0013

Abstract

Abstract:

Aims Photodamage to a shade-tolerant species is common due to a sudden increase in growth light intensity. However, it is unknown about the underlying mechanism of the sensitivity of the shade-tolerant species to high light. The objective of the present study was to elucidate the mechanisms involved in the inability of the typically shade-tolerant species Panax notoginseng to survive under natural full-light condition.

Methods The relative chlorophyll content (SPAD), photosynthetic parameters and chlorophyll fluorescence parameters were continuously examined in P. notoginseng when transferred from shade (10% of full sunlight) to full sunlight for three days.

Important findings The net photosynthetic rate (P_n) of P. notoginseng exposed to full sunlight condition showed a “double-peaked” diurnal curve, and P_n decreased with the prolonged days of full light treatment. The SPAD value, water utilization efficiency and light use efficiency were significantly decreased under full sunlight condition. Furthermore, the maximum fluorescence signal of the P700 reaction center, electron transfer rate of photosystem II (PSII), the maximum quantum efficiency of PSII under dark adaptation and maximum quantum efficiency of PSII under light adaptation were significantly lower in full sunlight than those under shading condition, while the fraction of energy passively dissipated in the forms of heat and fluorescence, energy dissipation due to acceptor side limitation of PSI, and cyclic electron flow were significantly higher under the full light condition. Moreover, the sudden increase in growth light intensity caused a significant change in the fluorescence induction kinetic curve and significantly increased the fluorescence yield on the donor and acceptor side of PSII. The oxygen-evolving complex activity in the donor side of PSII was impaired under full sunlight. Furthermore, the electron transfer in the acceptor side of PSII was inhibited and the over-reduction of the acceptor side of PSI was caused by PSI photoinhibition. The study reveals that the full sunlight might induce the irreversible damage to PSII and the moderate photoinhibition to PSI in shade-tolerant species, and it may be an important underlying mechanisms why the shade-tolerant speciesP. notoginseng cannot survive under full sunlight.

Key words: shade-tolerant species, full sunlight, photosynthesis, photosystem, photoprotection, Panax notoginseng

WU Hong-Min, SHUANG Sheng-Pu, ZHANG Jin-Yan, CUN Zhu, MENG Zhen-Gui, LI Long-Gen, SHA Ben-Cai, CHEN Jun-Wen. Photodamage to photosystem in a typically shade-tolerant species Panax notoginseng exposed to a sudden increase in light intensity[J]. Chin J Plant Ecol, 2021, 45(4): 404-419.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2021.0013

https://www.plant-ecology.com/EN/Y2021/V45/I4/404

Figures/Tables 11

Fig. 1 Diurnal pattern of photosynthetically active radiation (PAR) in shade treatment and full sunlight treatment.

Fig. 2 Diurnal pattern of humidity (A), air temperature (B) and atmospheric CO2 concentration (C) in shade treatment and full sunlight treatment.

Fig. 3 Diurnal pattern of relative chlorophyll content (SPAD value) in shade treatment and full sunlight treatment (mean ± SE, n = 7). *, significant difference between the two treatments at same measurement time ( p< 0.05).

Fig. 4 Diurnal pattern of net photosynthetic rate (A), intercellular CO2 concentration (B) and stomatal conductance (C) in shade treatment and full sunlight treatment (mean ± SE, n = 7). *, significant difference in gas exchange parameters between the two treatments at same measurement time ( p< 0.05).

Fig. 5 Water use efficiency (A) and light use efficiency (B) of Panax notoginseng exposed to shade and full sunlight conditions on the first, second and third day of the experiment, respectively (mean ± SE, n = 7). Different lowercase letters between shade and full sunlight conditions indicate signiﬁcant difference (p< 0.05).

Fig. 6 Diurnal pattern of maximum quantum efficiency under light adaptation (A), maximum quantum efficiency under dark adaptation (B) and non-photochemical quenching of PSII (C) in shade treatment and full sunlight treatment (mean ± SE, n = 7). *, significant difference between the two treatments at same measurement time ( p< 0.05).

Fig. 7 The maximum quantum efficiency under dark adaptation (A), potential activity of PSII reaction center (B) and the maximum fluorescence signal of the P700 reaction center (C) of Panax notoginseng exposed to shade and full sunlight conditions on the first, second and third day of the experiment, respectively (mean ± SE, n = 7). *, significant difference between the two treatments at same measurement day ( p< 0.05).

Fig. 8 Changes in rapid fluorescence induction kinetic curves (WO-J and Δ WO-J) in leaves of Panax notoginseng transferred from a shade environment with 10% transmittance to full sunlight. The abscissa is plotted on a linear time scale. W,the characteristic point at 100 μs (K point). Day 0, Sunlight-day 1, Sunlight-day 2, Sunlight-day 3 represent the exposure to low light, and the transfer to full sunlight for one, two and three days. Different lowercase letters indicate significant differences ( p< 0.05).

Fig. 9 Daily pattern of parameters related to the rapid fluorescence induction kinetic curve in leaves of Panax notoginsengtransferred from a shade environment with 10% transmittance to full sunlight (mean ± SE, n = 7). Different letters indicate signiﬁcant difference between shade and full sunlight conditions (p< 0.05).

Fig. 10 Effect of shade and full sunlight treatment on electron transfer and photosystem energy partitioning (mean ± SE, n = 7). LL, 10% transmittance-grown Panax notoginseng (230 μmol·m -2·s-1, 13:00); HL, full sunlight-grown Panax notoginseng (2 300 μmol·m -2·s-1, 13:00). Y(I), effective quantum yield of PSI; Y(ND), heat dissipation efficiency at the donors quantum yield of PSI; Y(NA), quantum yield of PSI non-photochemical energy dissipation due to acceptor; Y(II), effective quantum yield of PSII; Y(NPQ), quantum yield of energy dissipation in PSII; Y(NO), fraction of energy passively dissipated in forms of heat and fluorescence. ETR(I), electron transport rate of PSI; ETR(II), electron transport rate of PSII;CEF, cyclic electron flow around PSI. *, significant difference between the two treatments at same measurement day ( p< 0.05).

Fig. 11 Changes in electron transfer ratio in leaves of Panax notoginseng exposed to shade and full sunlight conditions on the first, second and third day of the experiment, respectively (mean ± SE, n = 7). ETR(I), electron transport rate of PSI; ETR(II), electron transport rate of PSII;CEF, cyclic electron flow around PSI. *, significant difference between the two treatments ( p< 0.05).

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