Susceptibility of green leaves and green flower petals of CAM orchid Dendrobium cv. Burana Jade to high irradiance under natural tropical conditions

Abstract

Photosynthetic rates of green leaves (GL) and green flower petals (GFP) of the CAM plant Dendrobium cv. Burana Jade and their sensitivities to different growth irradiances were studied in shade-grown plants over a period of 4 weeks. Maximal photosynthetic O 2 evolution rates and CAM acidities [dawn/dusk fluctuations in titratable acidity] were higher in leaves exposed to intermediate sunlight [a maximal photosynthetic photon flux density (PPFD) of 500-600 μmol m -2 s -1 ] than in leaves grown under full sunlight (a maximal PPFD of 1 000-1 200 μmol m -2 s -1 ) and shade (a maximal PPFD of 200-250 μmol m -2 s -1 ). However, these two parameters of GFP were highest in plants grown under the shade and lowest in full sun-grown plants. Both GL and GFP of plants exposed to full sunlight had lower predawn F v /F m [dark adapted ratio of variable to maximal fluorescence (the maximal photosystem 2 yield without actinic irradiation)] than those of shade-grown plants. When exposed to intermediate sunlight, however, there were no significant changes in predawn F v /F m in GL whereas a significant decrease in predawn F v /F m was found in GFP of the same plant. GFP exposed to full sunlight exhibited a greater decrease in predawn F v /F m compared to those exposed to intermediate sunlight. The patterns of changes in total chlorophyll (Chl) content of GL and GFP were similar to those of F v /F m . Although midday F v /F m fluctuated with prevailing irradiance, changes of midday F v /F m after exposure to different growth irradiances were similar to those of predawn F v /F m in both GL and GFP. The decreases in predawn and midday F v /F m were much more pronounced in GFP than in GL under full sunlight, indicating greater sensitivity in GFP to high irradiance (HI). In the laboratory, electron transport rate and photochemical and non-photochemical quenching of Chl fluorescence were also determined under different irradiances. All results indicated that GFP are more susceptible to HI than GL. Although the GFP of Dendrobium cv. Burana Jade require a lower amount of radiant energy for photosynthesis and this plant is usually grown in the shade, is not necessarily a shade plant.

Source-to-sink relationship between green leaves and green pseudobulbs of C₃ orchid in regulation of photosynthesis

“…Similar studies showed that nongreen petals of CAM Dendrobium Sonia were capable of photosynthesizing but at a lower amount of radiant energy (Khoo et al 1997, He et al 1998. He and Teo (2007) also reported that the photosynthetic rate of nonfolia photosynthetic organ such as green petals of Dendrobium Burana Jade was only 30-40% that of GL. Results of the present study (Figs.…”

Photosynthetic Light Utilization Efficiency, Water Relations and Leaf Growth of C3 and CAM Tropical Orchids under Natural Conditions

“…Orchids have protective stategies to overcome the stress from high irradiances and to help balance maximising photon energy utilization while minimising photoinhibition [6]. Previous studies reported higher tolerance to high PPFD and faster recovery from photoinbition in C 3 Oncidium orchid as compared to CAM Phalaenopsis orchid [29], greater photoprotection in leaves of C 3 orchid C. rochussenii under HL compared to LL [28], and recovery from photoinhibition in C 3 orchid Gramatophyllum speciosum in HL [27].…”

“…Plants grown under low irradiance may also experience a reduction in the photosynthetic rate, resulting in a decline in growth rate [5] [14]. Therefore it is necessary to strike a good balance in maximising photon energy utilization of leaves to increase photosynthetic activity whilst minimising photoinhibition [6].…”

Crassulacean Acid Metabolism in Epiphytic Orchids: Current Knowledge, Future Perspectives

“…Given that most existing information on the CO 2 exchange and carbon gain of vascular epiphytes is on leaves, data on the carbon gain in flowers are limited (Zotz & Hietz, 2001). Several studies have characterized the responses of flowers from CAM orchids to environmental conditions such as different light irradiances (Khoo et al, 1997;He et al, 1998;He & Teo, 2007) and temperatures (He et al, 1998) through the contents of pigments, acidity and certain photosynthetic parameters, such as PSII and Fv / Fm. Nevertheless, none of these surveys have, in fact, characterized CAM metabolism in flowers.…”