Photosynthesis Research

, Volume 35, Issue 3, pp 265–274

Light dependence of quantum yields of Photosystem II and CO2 fixation in C3 and C4 plants

  • Walter Oberhuber
  • Zi-Yu Dai
  • Gerald E. Edwards
Regular Paper

DOI: 10.1007/BF00016557

Cite this article as:
Oberhuber, W., Dai, Z. & Edwards, G.E. Photosynth Res (1993) 35: 265. doi:10.1007/BF00016557

Abstract

The light dependence of quantum yields of Photosystem II (ΦII) and of CO2 fixation were determined in C3 and C4 plants under atmospheric conditions where photorespiration was minimal. Calculations were made of the apparent quantum yield for CO2 fixation by dividing the measured rate of photosynthesis by the absorbed light [A/I=ΦCO2 and of the true quantum yield by dividing the estimated true rate of photosynthesis by absorbed light [(A+Rl)/IaCO2·], where RL is the rate of respiration in the light. The dependence of the ΦIICO2 and ΦIICO2* ratios on light intensity was then evaluated. In both C3 and C4 plants there was little change in the ratio of ΦIICO2 at light intensities equivalent to 10–100% of full sunlight, whereas there was a dramatic increase in the ratio at lower light intensities. Changes in the ratio of ΦIICO2 can occur because respiratory losses are not accounted for, due to changes in the partitioning of energy between photosystems or changes in the relationship between PS II activity and CO2 fixation. The apparent decrease in efficiency of utilization of energy derived from PS II for CO2 fixation under low light intensity may be due to respiratory loss of CO2. Using dark respiration as an estimate of RL, the calculated ΦIICO2* ratio was nearly constant from full sunlight down to approx 5% of full sunlight, which suggests a strong linkage between the true rate of CO2 fixation and PS II activity under varying light intensity. Measurements of photosynthesis rates and ΦII were made by illuminating upper versus lower leaf surfaces of representative C3 and C4 monocots and dicots. With the monocots, the rate of photosynthesis and the ratio of ΦIICO2 exhibited a very similar patterns with leaves illuminated from the adaxial versus the abaxial surface, which may be due to uniformity in anatomy and lack of differences in light acclimation between the two surfaces. With dicots, the abaxial surface had both lower rates of photosynthesis and lower ΦII values than the adaxial surface which may be due to differences in anatomy (spongy versus palisade mesophyll cells) and/or light acclimation between the two surfaces. However, in each species the response of ΦIICO2 to varying light intensity was similar between the two surfaces, indicating a comparable linkage between PS II activity and CO2 fixation.

Key words

C3 plantsC4 plantslightPhotosystem IIquantum yieldfluorescence

Abbreviations

A

measured rate of CO2 assimilation

A+RL

true rate of CO2 assimilation; e

CO2

estimate of electrons transported through PSII per CO2 fixed by RuBP carboxylase

f

fraction of light absorbed by Photosystem II

F'm

yield of PSII chlorophyll α fluorescence due to a saturating flash of white light under steady-state photosynthesis

Fs

variable yield of fluorescence under steady-state photosynthesis; PPFD-photosynthetic photon flux density

Ia

absorbed PPFD

PS II

Photosystem II

Rd

rate of respiration in the dark

RI

rate of respiration in the light estimated from measurement of Rd or from analysis of quantum yields

Φ

apparent quantum yield of CO2 assimilation under a given condition (A/absorbed PPFD)

Φ

true quantum yield of CO2 assimilation under a given condition [(A+RL)/(absorbed PPFD)]

Φ

quantum yield for photosynthetic O2 evolution

Φ

electrons transported via PS II per quantum absorbed by PS II

Copyright information

© Kluwer Academic Publishers 1993

Authors and Affiliations

  • Walter Oberhuber
    • 1
  • Zi-Yu Dai
    • 1
  • Gerald E. Edwards
    • 1
  1. 1.Department of BotanyWashington State UniversityPullmanUSA