The specific activities of acid (pH 5.5) and neutral (pH 7) DNases and RNases were determined in alfalfa (Medicago sativa L.) seedlings grown in the dark in the presence of 3.7 mM paraquat (PQ) or 1 mM roundup (RD). Seedlings were taken at 0, 1, 3, and 5 days. Plant growth parameters (plant height and fresh weight) were dramatically reduced under these conditions of growth comparing to the control (grown in water). The DNase and RNase specific activities of herbicide-treated seedlings were reduced. The reduction of activities ranged by about 50–90 and 15–70% in PQ- and RD-treated seedlings, respectively. In vitro, PQ- and RD-treated nucleic acids [single-stranded DNA (ssDNA), RNA, and plasmid DNA (pl-DNA)] were incubated with acid and neutral nucleases. Both enzymes were isolated and purified from alfalfa seedlings. Electrophoretic analysis on agarose gel of the above incubated mixtures revealed the following: (a) neutral nuclease (pH 7) was capable of hydrolyzing PQ-treated ssDNA while acid nuclease (pH 5.5) was incapable. This could be due to the fact that acid and neutral nucleases displayed different base linkage specificity toward ssDNA; (b) RD formed strong complexes with ssDNA that were unable to be hydrolyzed by both nucleases; (c) in contrast, both enzymes were capable of hydrolyzing PQ- or RD-treated RNA; (d) neutral nuclease was capable of nicking and linearizing both PQ- and RD+treated pl-DNA while acid nuclease had the same activity only toward the PQ-treated pl-DNA; (e) the enzyme activities were not inhibited in the presence of both herbicides. The data suggest that the complexes of PQ or RD with DNA should not be functional substrates of nucleases, and consequently cell processes (e.g., metabolism of nucleic acids, gene expression, replication), in which DNA and nucleases are involved, could be disturbed.
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