Selective action of atrazine in callus cultures of Solanum nigrum and Nicotiana tabacum.

Callus cultures, obtained from Nicotiana tabacum and from two biotypes (atrazine-resistant and susceptible) of Solanum nigrum, were cultured in the presence of atrazine (0 - 35 - 70 uM). Herbicide effects were observed with two sucrose levels (2.5 and 10 g/L) and evaluated by dry weight measurements. The higher sucrose concentration assured a greater growth of the cultures. Atrazine, with both sugar levels, selectively affected the callus proliferation: susceptible cultures bleached within 15 days and were unable to grow, in contrast with the resistant ones, which maintained a green colour and grew similar to the untreated calli. It is possible that growth inhibition depend on secondary effects following the interruption of electon flow at the photosystem II level.