05).Figure 2Effects of L-DOPA on tyrosine ammonia-lyase (TAL). *Values (N = 3 �� SE) selleck chemical differ statistically (Dunnett’s multiple comparison test) from control (P < 0.05).Figure 3Effects of L-DOPA on soluble (a) and cell wall-bound (b) peroxidases (POD). *Values (N = 5 �� SE) differ statistically (Dunnett's multiple comparison test) from control (P < 0.05).The lignin content increased from 15.3 to 25.7% after treatment with the two highest concentrations of L-DOPA, respectively, in comparison to the control (159.4 �� 3.01mgg?1 dry weight) (Figure 4). The results obtained after exposure of maize seedlings to L-DOPA revealed that the content of phenylalanine and tyrosine increased by 46% and 18.9%, respectively, in comparison to the control (Table 2).Figure 4Effects of L-DOPA on lignin contents.

*Values (N = 4 �� SE) differ statistically (Dunnett’s multiple comparison test) from control (P < 0.05).Table 2Changes in the levels of tyrosine and phenylalanine of maize seedlings treated with L-DOPA for 24h. 4. DiscussionIn the current work, we showed that the growth (length and weight) of maize roots was significantly affected by L-DOPA (Table 1), which is a feature common to the effects of different allelochemicals in plants [2, 3]. The reduction of root growth by the action of L-DOPA at different concentrations has been described in several plant species [26�C28] although some of them were resistant to the allelochemical [13]. Since L-DOPA reduced the growth of maize roots (Table 1), its role as a potent allelochemical has been strengthened.

Decrease in root length has been related to the cell wall lignification induced by allelochemicals. In general, lignification stiffens the cell wall with concomitant increases in PAL and POD activities. In fact, increases of PAL activity correlate with reduction of root growth and lignin production in maize, cucumber, and soybean exposed to the action of phenylpropanoid allelochemicals [22, 29�C31]. In addition, soluble and cell wall-bound POD activities increase concomitantly with lignin production in roots of maize [29], cucumber [30], and soybean [22, 32, 33]. With respect to L-DOPA, Soares et al. [19] observed a reduced root length of soybean followed by increases in PAL and POD activities and lignin content.

In contrast to the abovementioned reports, we have found that L-DOPA decreased the maize root growth and PAL, TAL, and soluble and cell wall-bound POD activities (Figures (Figures1to1to 3) but slightly increased the lignin content at high concentrations (Figure 4). It is not a bottleneck effect, however, because the apparent contradiction can be refuted by the complexity of the shikimate and phenylpropanoid pathways in plants. The shikimate pathway, Dacomitinib which leads to the synthesis of aromatic amino acids such as phenylalanine and tyrosine, and the phenylpropanoid pathway towards the synthesis of lignin are clearly interconnected [18].