A. Mostowska et al., EFFECT OF 2,2'-BIPYRIDYL, A PHOTODYNAMIC HERBICIDE, ON CHLOROPLAST ULTRASTRUCTURE, PIGMENT CONTENT AND PHOTOSYNTHESIS RATE IN PEA-SEEDLINGS, Acta Physiologiae Plantarum, 18(2), 1996, pp. 153-164
The effect of a foliar application of 2.2'-bipyridyl (2.2'-B) at conce
ntrations of 5, 10 or 30 mM on ultrastructure of mesophyll cells, chlo
rophyll (Chl) and carotenoid (Car) contents, photosynthetic activity r
ate (Pn) and dark respiration rate (R) and chlorophyll fluorescence in
pea seedlings was examined. Pea plants were resistant to a low dose (
5 mM) with respect to morphology, pigment level and structure of mesop
hyll cells. However, 10 and 30 mM 2.2'-B and illumination caused a los
s of turgor of treated plants and photooxidative perturbations at the
structural and functional level in chloroplasts. Photosystem II (PS II
) was the primary target of 2.2'-B action. 2.2'-B treatment and subseq
uent illumination caused direct and secondary reactions. The former, c
aused by processes which took: place even prior to light exposure, was
first expressed and monitored by changes of Chl fluorescence and Pn.
The latter, subsequent slow reactions, were induced by light, required
longer illumination time and led to destructive changes in mesophyll
cell ultrastructure including dilation of thylakoid membranes and endo
plasmic reticulum (ER) cisternae and disruption of the chloroplast env
elope as well as a decrease in Chl and Car contents. These slow reacti
ons were the result of the rapid ones as well as the result of light-i
nduced photooxidative mechanism based on the process of porphyrin phot
osensitizing.