Abstract
Vanilla orchid, which is well-known for its flavor and fragrance, is cultivated in tropical and subtropical regions. This shade-loving plant is very sensitive to high irradiance. In this study, we show that vanilla chloroplasts started to have avoidance movement when blue light (BL) was higher than 20 μmol m−2s−1 and significant avoidance movement was observed under BL irradiation at 100 μmol m−2s−1 (BL100). The light response curve indicated that when vanilla was exposed to 1000 μmol m−2s−1, the electron transport rate (ETR) and photochemical quenching of fluorescence (qP) were significantly reduced to a negligible amount. We found that if a vanilla orchid was irradiated with BL100 for 12 days, it acquired BL-acclimation. Chloroplasts moved to the side of cells in order to reduce light-harvesting antenna size, and chloroplast photodamage was eliminated. Therefore, BL-acclimation enhanced vanilla orchid growth and tolerance to moderate (500 μmol m−2s−1) and high light (1000 μmol m−2s−1) stress conditions. It was found that under high irradiation, BL-acclimatized vanilla maintained higher ETR and qP capacity than the control without BL-acclimation. BL-acclimation induced antioxidant enzyme activities, reduced ROS accumulation, and accumulated more carbohydrates. Moreover, BL-acclimatized orchids upregulated photosystem-II-associated marker genes (D1 and PetC), Rubisco and PEPC transcripts and sustained expression levels thereof, and also maximized the photosynthesis rate. Consequently, BL-acclimatized orchids had higher biomass. In short, this study found that acclimating vanilla orchid with BL before transplantation to the field might eliminate photoinhibition and enhance vanilla growth and production.
Highlights
Vanilla orchids make up about 110 species in the orchid family (Orchidaceae) and boast the family’s only edible fruit
To understand whether vanilla orchid chloroplast movement is dependent on blue light (BL) or red light, we exposed vanilla orchid leaves (L3) to monochromic light-emitting diode (LED) red light (RL, λmax = 660 nm) and blue light (BL, λmax = 450 nm), respectively, at a light intensity of 50 μmol m−2s−1 for 5 h
analysis of variance (ANOVA) analysis data indicated that BL intensity significantly affected the chloroplast movement of L3 and LM, but the interaction of BL × Time was of no significant difference (Table 1)
Summary
Vanilla orchids make up about 110 species in the orchid family (Orchidaceae) and boast the family’s only edible fruit. Market demand for natural vanillin is increasing, and vanilla orchid is cultivated in many tropical and subtropical zones [2]. Vanilla orchid performs crassulacean acid metabolism (CAM) photosynthesis. For a CAM plant, PAR intensity during the day affects the rate of mobilization of organic acids from the vacuole (Phase III) [3]. Vanilla orchid is a shade-loving plant that is very sensitive to high radiation. Support trees should have a dense canopy to provide 70% to 80% shade [4]. A high light of 67% relative illumination inhibits vanilla growth, reduces Fv/Fm, and decreases CO2 uptake. It has been found that vanilla has higher photosynthesis and biomass growth under intermediate levels of radiation of 17% to 31% relative illumination [5]
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