Metabolic responses of tomato plants to metribuzin herbicide by in vivo and in vitro techniques

The effect of metribuzin at different doses [0.25, 0.5, 0.75 and 1.0kg ha-1] was studied on intact pot normally-grown seedlings of two tomato genotypes [Lycopersicon esculentum Mill, cv. Karnak vfnt F-1 and Castle rock]. The herbicide caused significant inhibitions in dry weight and protein contents of shoots and roots of both tomato genotypes. Significant reductions in chlorophyll, carotenoids, glucose, sucrose and starch were observed. The reduction was more pronounced at higher metribuzin doses. Possible tolerance to the herbicide in both genotypes was checked using tissue culture methods. Cotyledons and leaf discs from shoots regenerated on media containing different concentrations of metribuzin [0, 0.63, 1.25, 2.5, 5 and 10 mgM]were used to initiate three successive cycles of selection. Similar to potted plants, significant reductions in dry weight and protein content in shoots and roots of the in vitro selected plants were observed as well as in contents of chlorophylls, carotenoids, glucose, sucrose and starch of both tomato genotypes. The inhibition was remarkable at the high concentrations of metribuzin throughout the three cycles of selection. The magnitude of inhibition was relatively lesser in the 3rd cycle compared to the 1st or the 2nd cycles. Therefore, the effects of metribuzin on tomato appeared as declined after three cycles of the in vitro selection. Such decline could be regarded as a partial recovery response. This recovery response after three cycles of in vitro selection could point to a possibility of some developed resistance to the herbicide throughout the successive cycles

In-vitro induction of tomato resistance to metribuzin herbicide. Secondary metabolism indices

The effect of metribuzin at different doses [0.25, 0.5, 0.75 and 1.0 kg ai ha-1] was studied on original intact seedlings of two tomato variants [Lycopersicon esculentum Mill, cv. Karnak vfnt F-1 and Castle rock]. Metribuzin significantly reduced the growth parameters [shoot and root length, fresh and dry weight] of shoots and roots of both variants. Low doses of the herbicide significantly increased anthocyanin content and activities of phenylalanine ammonia lyase [PAL EC 4.3.1.5], tyrosine ammonia lyase [TAL EC 4.3.1] and chalcone isomerase [CI; EC 5.5 1.5] in both tomato variants. While, high doses seemed [if any] to have no effect. An attempt was conducted to check the effectiveness of cyclical in vitro selection for increasing resistance to metribuzin. Cotyledons and leaf explants from shoots regenerated on media containing different concentrations of metribuzin [0, 0.63, 1.25, 2.5, 5 and 10 muM] were used to initiate three successive cycles of selection. Throughout the three cycles of selection, metribuzin resulted in significant reductions in growth parameters of shoots of both variants. The reduction was more greater with the high concentrations of metribuzin. The reduction was relatively lesser in the 3rd cycle than the 1st cycle or the 2nd cycle. There were increases in anthocyanin contents of shoots and roots of both variants at all concentrations of metribuzin; high concentrations seemed to level off these increases. Only low metribuzin concentrations increased activities of PAL, TAL and CI of both variants. The response of secondary metabolism activities to the herbicide was lesser in plantlets selected from the 3rd cycle than in the 1st cycle