Blue Light Acclimation Reduces the Photoinhibition of Phalaenopsis aphrodite (Moth Orchid).

Swee-Suak Ko,Chung-Min Jhong,Ming-Che Shih

doi:10.3390/ijms21176167

Abstract

The moth orchid is an important ornamental crop. It is very sensitive to high light irradiation due to photoinhibition. In this study, young orchid tissue culture seedlings and 2.5” potted plants pretreated under blue light (BL, λmax = 450 nm) at 100 µmol m−2 s−1 for 12 days (BL acclimation) were found to have an increased tolerance to high light irradiation. After BL acclimation, orchids had an increased anthocyanin accumulation, enhanced chloroplast avoidance, and increased chlorophyll fluorescence capacity whenever they were exposed to high light of 1000 μmol m−2 s−1 for two weeks (HL). They had higher Fv/Fm, electron transport rate (ETR), chlorophyll content, catalase activity and sucrose content when compared to the control without BL acclimation. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) showed that transcript levels of phototropins, D1, RbcS, PEPCK, Catalase and SUT2 were upregulated in the BL-acclimated orchids. Consequently, BL acclimation orchids had better growth when compared to the control under long-term high light stress. In summary, this study provides a solution, i.e., BL acclimation, to reduce moth orchid photoinhibition and enhance growth before transplantation of the young tissue culture seedlings and potted plants into greenhouses, where they usually suffer from a high light fluctuation problem.

Highlights

Photosynthesis converts light energy into chemical energy in photosynthetic plants and assimilates CO2 into carbohydrates
These data indicated that when the moth orchid is exposed to high irradiation, it does not turn on the non-photochemical quenching mechanism, but the electron transport rate (ETR) and the oxidation state of the photosystem II are the most sensitive parameters in the moth orchid in response to light stress
This study further indicated that BL100 treatment for 12 days (T0) enhanced photo-acclimation in moth orchids

Summary

Introduction

Photosynthesis converts light energy into chemical energy in photosynthetic plants and assimilates CO2 into carbohydrates. Photosystems (PS) consist of PSI and PSII. They are located in the thylakoid membranes and are the functional units for photosynthesis. The electron transport PSII is inhibited and its protein structure is damaged. PSI can be damaged if the electron transport from PSII is limited [3]. Photoinhibition reduces the quantum yield and light-saturated photosynthetic rate (Amax) [4]. Plants have developed several strategies to cope with photoinhibition They turn on photoprotection mechanisms, including the regulation of light absorption and dissipation of excess light energy. Plants may change their leaf area, leaf angle and chloroplast movement, and may reduce their LHC antenna size. Once excess light has been absorbed, the plant will dissipate excess excitation energy through thermal dissipation [3,4]

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