Ng. Averina et al., FORMATION OF CHLOROPHYLL BIOSYNTHESIS INTERMEDIATES IN BEAN, CUCUMBERAND BARLEY SEEDLINGS TREATED WITH 5-AMINOLEVULINIC ACID AND HOMOCYSTEINE, Photosynthetica, 32(1), 1996, pp. 45-52
Porphyrin accumulation was investigated in intact green bean (Phaseolu
s vulgaris), cucumber (Cucumis sativus) and barley (Hordeum vulgare) s
eedlings that were placed for 17 h into darkness after having been spr
ayed with solutions of natural metabolites of 5-aminolevulinic acid (A
LA), a specific porphyrin precursor, and homocysteine, an inhibitor of
S-adenosyl-L-methionine:Mg-protoporphyrin IX methyltransferase. At co
ncentrations of 3-15 mM, homocysteine in combination with ALA, in cont
rast with the action of ALA alone, strengthened both the porphyrinogen
esis in the dicotyledons investigated and the porphyrin-induced photod
amage that resulted in plant death after 4 d of continuous irradiation
of previously darkened seedlings. Further increase of the homocystein
e concentrations resulted in a gradual decrease of the stimulation of
porphyrin accumulation with a loss of herbicidal activity. Primary lea
ves of barley as monocotyledons were much less sensitive to the new he
rbicide compositions than the dicotyledons investigated.