Effect of 1.10-phenanthroline, a photodynamic herbicide on the developmentand structure of maize chloroplasts

Effect of low (5 mmol.dm(-3)) and high (10 or 20 mmol.dm(-3)) doses of 1.10 -phenanthroline (Phe), a photodynamic herbicide, on the development of chlo roplasts ts in etiolated and subsequently illuminated maize seedlings and o n the structure of already developed chloroplasts of green maize seedlings was examined. Etiolated and then irradiated plants were resistant to 5 mmol .dm(-3) of Phe with respect to morphology, however Phe caused inhibition of greening and of grana formation. Higher Phe concentrations followed by exp osure to light caused not only total inhibition of greening but also dilati on of thylakoids, swelling of chloroplasts, and finally total destruction o f chloroplast structure. Application of Phe in the same concentrations to g reen plants revealed that they were resistant to low dose of Phe with respe ct to morphology and structure of chloroplasts, however 10 and 20 mmol.dm(- 3) Phe and illumination caused the loss of turgor of treated plants and oth er photooxidative damages seen at the ultrastructural level. We concluded t hat maize, as representant of monocotyledonous plants, is resistant to low (5 mmol.dm(-3)) Phe concentration. Higher (10 or 20 mmol.dm(-3)) concentrat ions, used to determine the site of damage and mode of action of Phe on the level of cell revealed that action of photodynamic herbicides is based on standard photoinhibition mechanism and also probably on their chelating pro perties.