The functional role of the photosynthetic apparatus in the recovery of Brassica ofBrassica napus plants from pre-emergent metazachlor exposure

Metazachlor is a chloroacetamide herbicide, frequently used in Brassica napus cultivations around theworld. Its primary target is the inhibition of very long chain fatty acid biosynthesis. This study included amorphological and physiological screening of hydroponically grown B. napus, exposed to a concentrationrange of 0, 0.25, 0.50, 0.75 and 1.0 kg metazachlor per hectare. The results indicate that within a monthafter application, growth and development of B. napus are severely affected by low metazachlor doses.At intermediate metazachlor concentrations, loss of phosphorous and potassium from the plant tissuessuggests destabilisation of cellular membranes, which may be a direct consequence of metazachlor appli-cation. This membrane instability could be indirectly linked with alterations of electron transport anda reduction of carbon assimilation. At increased metazachlor doses of 0.75 kg a.i. ha−1, pigment concen-trations are strongly reduced. However, chlorophyll fluorescence parameters seem to remain unaffectedat metazachlor doses up to 0.75 kg a.i. ha−1. At a metazachlor concentration of 1.0 kg a.i. ha−1, negativeeffects are observed on all tested parameters, resulting in limited survival. The results indicate photosyn-thesis is assured at intermediate metazachlor concentrations for the cost of growth and development. Itis clear that photosynthesis plays a key role in the survival strategy of young plants to overcome initiallyinduced chemical stress.