Abstract
Anoectochilus roxburghii was grown under different shade treatments–50%, 30%, 20%, and 5% of natural irradiance–to evaluate its photosynthetic characteristics, chloroplast ultrastructure, and physiology. The highest net photosynthetic rates and stomatal conductance were observed under 30% irradiance, followed in descending order by 20%, 5%, and 50% treatments. As irradiance decreased from 50% to 30%, electron transport rate and photochemical quenching increased, while non-photochemical quenching indexes declined. Reductions in irradiance significantly increased Chl a and Chl b contents and decreased Chl a/b ratios. Chloroplast ultrastructure generally displayed the best development in leaves subjected to 30% irradiance. Under 50% irradiance, leaf protein content remained relatively stable during the first 20 days of treatment, and then increased rapidly. The highest peroxidase and superoxide dismutase levels, and the lowest catalase activities, were observed in plants subjected to the 50% irradiance treatment. Soluble sugar and malondialdehyde contents were positively correlated with irradiance levels. Modulation of chloroplast development, accomplished by increasing the number of thylakoids and grana containing photosynthetic pigments, is an important shade tolerance mechanism in A. roxburghii.
Highlights
Anoectochilus roxburghii, a member of the Orchidaceae, is a valued plant species in many Asian countries, where it is used for ornamental, culinary, and medicinal purposes
The objectives of the present study were to quantify the influences of different shading levels on photosynthetic characteristics, chloroplast ultrastructure, and physiology of A. roxburghii, to determine optimum light intensity for plant growth, and to expand our understanding of its shade-tolerance abilities and mechanisms
The Pn value was always highest at 30% irradiance, followed at most time points by 20%, 5%, and 50% irradiance treatments
Summary
Anoectochilus roxburghii, a member of the Orchidaceae, is a valued plant species in many Asian countries, where it is used for ornamental, culinary, and medicinal purposes. Because of its unique medicinal properties, such as its notable curative effects of clearing heat and cooling blood, eliminating dampness, and detoxification, A. roxburghii has been called ‘‘the king of medicine’’ [1,2]. Recent research has demonstrated that the entire plant possesses medicinal properties, such as antioxidant, anti-inflammatory, and antitumor activities [3,4]. A. roxburghii has been traditionally harvested mainly from wild populations. The species has become endangered, as a result of human overexploitation coupled with its specific environmental growth requirements. Artificial cultivation is beginning to be carried out in various locations in China
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