Physiological responses and photo-protective mechanisms of two Rhododendron plants to natural sunlight after long term shading

doi:10.17521/cjpe.2015.0106

Abstract

Abstract:

AimsResponses of plants to increased irradiance are governed by two strategies: an increase in the utilization of absorbed light and photo-protective mechanisms. Varied physiological responses to increased irradiance were observed in plant species with differing adaptabilities to light regimes. This research aims to explore the physiological responses and photo-protective mechanisms of two Rhododendron plants to changes in light regimes. MethodsChlorophyll fluorescence parameters and rapid light curves were measured for leaves of R. hybrida (a shade-tolerant species) and R. simsii (a light-loving and shade-tolerant species) following exposure to sunlight for five days after growing in the shade for one year.Important findings Natural sunlight decreased the efficiency of photochemical reaction by reducing the fraction of incident light in photochemical energy utilization and decreased thermal dissipation through regulating energy dissipation in photosystem II (PSII) in the leaves of R. hybrida. As a result, natural sunlight induced the accumulation of excess excitation energy in PSII, and caused photo-inhibition and even photodamage in the leaves of R. hybrida, which was suddenly transferred from long-term shading to sun exposures. The acclimation capacity to changes of growth light regimes was stronger in R. simsii than in R. hybrida, due to a higher capability for photochemical reaction, thermal dissipation and cyclic electron flows around photosystem I in the leaves of R. simsii. Rhododendron simsii could utilize a high fraction of incident light in photochemistry and regulate energy dissipation in PSII to protect the photosynthetic apparatus under both shading and natural sunlight condition. Therefore, high light intensity under natural sunlight did not cause photo-inhibition in R. simsii.

Key words: Rhododendron, natural sunlight, photoinhibition, photoprotection, shading

HU Wen-Hai,ZHANG Si-Si,XIAO Yi-An,YAN Xiao-Hong. Physiological responses and photo-protective mechanisms of two Rhododendron plants to natural sunlight after long term shading[J]. Chin J Plan Ecolo, 2015, 39(11): 1093-1100.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2015.0106

https://www.plant-ecology.com/EN/Y2015/V39/I11/1093

Figures/Tables 4

Table 1 Effects of natural sunlight exposure after long-term shading on the maximal quantum efficiency of PSII (Fv/Fm), initial slope (α), maximum photosynthetic electron flow (Jmax) and maximum irradiance (PARsat) in Rhododendron hybrida and R. simsii leaves (mean ± SE, n = 5)

参数 Parameter	比利时杜鹃 R. hybrida		杜鹃 R. simsii
参数 Parameter	遮阴 Shade	全光照 Sun	遮阴 Shade	全光照 Sun
F_v/F_m	0.793 ± 0.004^a	0.494 ± 0.029^b	0.817 ± 0.002^a	0.780 ± 0.002^b
α	0.392 ± 0.013^a	0.238 ± 0.018^b	0.333 ± 0.003^a	0.327 ± 0.007^a
J_max (μmol·m^-2·s^-1)	64.9 ± 6.8^a	37.8 ± 5.3^b	63.1 ± 8.3^a	74.9 ± 4.4^a
PAR_sat (μmol·m^-2·s^-1)	808.8 ± 37.0^a	818.4 ± 21.2^a	849.4 ± 24.3^b	943.2 ± 17.2^a

Fig. 1 Rapid light curves of ETR(II) and ETR(I)/ETR(II) in Rhododendron hybrida and R. simsii leaves during transition from long-term shading to 5 days of sun exposures (mean ± SE, n = 5). ETR(I), ETR(II), apparent electron transport rate at PSI and PSII; PAR, photosynthetic active radiation.

Fig. 2 Rapid light curves of photochemical quenching (qP) and non-photochemical quenching (NPQ) in Rhododendron hybrida and R. simsii leaves during transition from long-term shading to 5 days of sunlight exposures (mean ± SE, n = 5). PAR, photosynthetic active radiation.

Fig. 3 Rapid light curves of effective PSII quantum (Y(II)), quantum yield of regulated energy dissipation (Y(NPQ)) and quantum yield of nonregulated energy dissipation (Y(NO)) in Rhododendron hybrida and R. simsii leaves during transition from long-term shading to 5 days of sunlight exposures (mean ± SE, n = 5). PAR, photosynthetic active radiation.

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