S. Nogues et Nr. Baker, EVALUATION OF THE ROLE OF DAMAGE TO PHOTOSYSTEM-II IN THE INHIBITION OF CO2 ASSIMILATION IN PEA LEAVES ON EXPOSURE TO UV-B RADIATION, Plant, cell and environment, 18(7), 1995, pp. 781-787
Mature pea (Pisum sativum L., cv, Meteor) leaves were exposed to two l
evels of UV-B radiation, with and without supplementary UV-C radiation
, during 15 h photoperiods. Simultaneous measurements of CO2 assimilat
ion and modulated chlorophyll fluorescence parameters demonstrated tha
t irradiation with UV-B resulted in decreases in CO2 assimilation that
are not accompanied by decreases in the maximum quantum efficiency of
photosystem II (PSII) primary photochemistry, Increased exposure to U
V-B resulted in a further loss of CO2 assimilation and decreases in th
e maximum quantum efficiency of PSII primary photochemistry, which wer
e accompanied by a loss of the capacity of thylakoids isolated from th
e leaves to bind atrazine, thus demonstrating that photodamage to PSII
reaction centres had occurred, Addition of W-C to the UV-B treatments
increased markedly the rate of inhibition of photosynthesis, but the
relationships between CO2 assimilation and PSII characteristics remain
ed the same, indicating that UV-B and UV-C inhibit leaf photosynthesis
by a similar mechanism, It is concluded that PSII is not the primary
target site involved in the onset of the inhibition of photosynthesis
in pea leaves induced by irradiation with UV-B.