Journal of Biosciences

, Volume 12, Issue 3, pp 211–218 | Cite as

Immediate effects of pyridazinone herbicides on photosynthetic electron transport in algal systems

  • Karunyal Samuel
  • Salil Bose


Pyridazinone herbicides, SANDOZ 9785 (4-chloro-5-dimethylamino2-phenyl-3-(2H) pyridazinone), SANDOZ 9789 (4-chloro-5 (methylamino)-2-(α, α, α-trifluoro-m-tolyl-3-(2H) pyridazinone) and SANDOZ 6706 (4-chloro-5-(methylamino)-2-(α, α, α-trifluoro-m-tolyl-3-(2H) pyridazinone) inhibited photosystem II electron transport inChlorella protothecoides, when the herbicides were added to the assay medium. The inhibitory eficiency varied with the algal species and the nature of substitution of pyridazinones. Using 3 algal systemsviz., Chlorella, Scenedesmus andAnacystis, the I50 value of for the inhibition of photosynthesis of 3 substituted pyridazinones (SANDOZ 9785, SANDOZ 6706 and SANDOZ 9789) were determined. SANDOZ 9789 was found to be the weakest inhibitor of photosystem II electron transport (H2O→ benzoquinone) as compared to SANDOZ 9785 and SANDOZ 6706. In general, the order of inhibition could be given as SANDOZ 6706 >- SANDOZ 9785 > SANDOZ 9789. The I50 value of photosynthetic particles obtained fromChlorella cells was similar to that of whole cells, suggesting that the cell wall ofChlorella did not act as a barrier for the herbicide action. Studies on the light intensity dependence of SANDOZ 9785 inhibition of electron transport (H2O→ benzoquinone) showed that the light-dependent portion of the curve was more sensitive than the light independent portion of the curve. It is suggested that the site of action was on the reducing side of photosystem II.


Pyridazinone herbicides Chlorella protothecoides Scenedesmus Anacystis electron transport 

Abbreviations used


Photosystem II

SAN 9785

SANDOZ 9785 (4-chloro-5-dimethylamino-2-phenyl-3-(2H) pyridazinone)

SAN 9789

SANDOZ 9789 (4-chloro-5 (methylamino)-2-(α,α,α-trifluoro-m-tolyl-3-(2H) pyridazinone)

SAN 6706

SANDOZ 6706 (4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl-3-(2H) pyridazinone)




photosystem I


primary acceptor of PS II




3-(3,4-dichlorophenyl)-1,1 -dimethyl urea


concentraüon required to cause 50% inhibition


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Copyright information

©  Indian Academy of Sciences 1987

Authors and Affiliations

  • Karunyal Samuel
    • 1
  • Salil Bose
    • 1
  1. 1.School of Biological SciencesMadurai Kamaraj UniversityMaduraiIndia

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