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Photosynthetica

, 45:214 | Cite as

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

  • J. He
  • L. C. D. Teo
Original Papers

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 O2 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 Fv/Fm [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 Fv/Fm in GL whereas a significant decrease in predawn Fv/Fm was found in GFP of the same plant. GFP exposed to full sunlight exhibited a greater decrease in predawn Fv/Fm 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 Fv/Fm. Although midday Fv/Fm fluctuated with prevailing irradiance, changes of midday Fv/Fm after exposure to different growth irradiances were similar to those of predawn Fv/Fm in both GL and GFP. The decreases in predawn and midday Fv/Fm 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.

Additional key words

CAM acidity chlorophyll electron transport rate fluorescence induction photosynthetic O2 evolution photosynthetic photon flux density quenching 

Abbreviations

Chl

chlorophyll

DM

dry matter

ETR

electron transport rate

F0

minimal fluorescence yield of a “darkadapted” sample

F0

modulated fluorescence during brief interruption of actinic irradiation in the presence of far-red irradiation

Fm and Fv

maximal and variable fluorescence yields obtained from a dark-adapted sample upon application of a saturating pulse of radiation, respectively

Fm

maximal fluorescence yield at any given time under irradiation

Fs

Chl fluorescence yield during irradiation

GFP

green flower petal

GL

green leaf

HI

high irradiance

PPFD

photosynthetic photon flux density

PS2

photosystem 2

qN

non-photochemical quenching of Chl fluorescence

qP

photochemical quenching of Chl fluorescence

TA

titratable acidity

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Copyright information

© Institute of Experimental Botany, ASCR 2007

Authors and Affiliations

  1. 1.Natural Sciences and Science Education Academic Group, National Institute of EducationNanyang Technological UniversitySingapore

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