The relationship of nitrogen source and in vivo nitrate reductase actiity to root formation in Euphorbia esula cell suspension cultures.

Root formation and in vivo nitrate reductase (NR) activity were determined in leafy spurge cell suspensions. Cells grown in B5 media with 1 mg L(-1) 2,4-D were transferred to B5 media without 2,4-D, but containing either high (92:8) or low (15:85) ratios of nitrogen as NO 3 (-) -N:NH 4 (+) -N. In older cell lines root formation occurred only in the low NO 3 (-) medium with =<30 roots per flask. In younger cell lines root numbers were greatest in the high NO 3 (-) medium (1000 to 3000 per flask). Cells grown in low NO 3 (-) medium were about one-third the final dry weight as those in high NO 3 (-) medium. Root length was consistently greater for cell lines of all ages in the low NO 3 (-) medium. Developmental profiles of NR activity were similar in cell lines of all ages, whether or not roots were formed. NR activity was lower, however, in cultures grown in low NO 3 (-) medium compared to high NO 3 (-) medium. There was no consistent relationship between NR activity and root initiation. Therefore, nitrate reductase does not appear to be a primary target for regulation of leafy spurge growth by chemical application.