Planta

, Volume 197, Issue 4, pp 583–591

High susceptibility to photoinhibition of young leaves of tropical forest trees

  • G. Heinrich Krause
  • Aurelio Virgo
  • Klaus Winter
Article

DOI: 10.1007/BF00191564

Cite this article as:
Krause, G.H., Virgo, A. & Winter, K. Planta (1995) 197: 583. doi:10.1007/BF00191564

Abstract

Photoinhibition of photosynthesis was studied in young (but almost fully expanded) and mature canopy sun leaves of several tropical forest tree species, both under controlled conditions (exposure of detached leaves to about 1.8 mmol photons·m-2·s-1) and in the field. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence emission (FV/FM) and also by gas-exchange measurements. For investigations in situ, young and mature leaves with similar exposure to sunlight were compared. The results show a consistently higher degree of photoinhibition in the young leaves. In low light, fast recovery was observed in both types of leaves in situ, as well as in the laboratory. The fluorescence parameter 1 — FS/F′M (where FS = stationary fluorescence and f′M = maximum fluorescence during illumination) was followed in situ during the course of the day in order to test its suitability as a measure of the photosynthetic yield of photosystem II (PSII). Electron-transport rates were calculated from these fluorescence signals and compared with rates of net CO2 assimilation. Measurements of diurnal changes in PSII ‘yield’ confirmed the increased susceptibility of young leaves to photoinhibition. Calculated electron transport qualitatively reflected net CO2 uptake in situ during the course of the day. Photosynthetic pigments were analyzed in darkened and illuminated leaves. Young and mature leaves showed the same Chl a/b ratio, but young leaves contained about 50% less Chl a + b per unit leaf area. The capacity of photosynthetic O2 evolution per unit leaf area was decreased to a similar extent in young leaves. On a Chl basis, young leaves contained more α-carotene, more xanthophyll cycle pigments and, under strong illumination, more zeaxanthin than mature leaves. The high degree of reversible photoinhibition observed in these young sun leaves probably represents a dynamic regulatory process protecting the photosynthetic apparatus from severe damage by excess light.

Key words

Chlorophyll fluorescence Photoinhibition (photosynthesis) Photosynthetic gas exchange Photo-system II Tropical forest species Xanthophyll cycle 

Abbreviations

Chl

chlorophyll

FO

initial chlorophyll fluorescence

FM

maximum total fluorescence

FV

maximum variable fluorescence (= FM — FO)

JF

rate of PSII-driven electron transport ΦPSII = photosynthetic yield of PSII

PFD

photon flux density (400–700 nm)

PS

photosystem

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • G. Heinrich Krause
    • 1
  • Aurelio Virgo
    • 1
  • Klaus Winter
    • 1
  1. 1.Smithsonian Tropical Research InstituteBalboaRepublic of Panama
  2. 2.Institute of Plant Biochemistry, Heinrich Heine University DüsseldorfDüsseldorfGermany