Impact of sulphur and nitrogen application on seed and xanthotoxin yield in Ammi majus L.

Field experiments were conducted to determine the physiological and biochemical basis of the interactive effect of sulphur (S) and nitrogen (N) application on seed and xanthotoxin yield of Ammi majus L. Six treatments were tested (T1=control-without manure and fertilizers, T2=manure @ 9 kg plot-1-10 t ha-1, T3=S0N50 K25P25, T4=S40N50K25P25, T5=S40N100K25P25, T6=S20+20N50+50 K25P25). Nitrate reductase (NR) activity and ATP-sulphurylase activity in the leaves were measured at various phenological stages, as the two enzymes catalyze rate-limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these two enzymes were strongly correlated with seed and xanthotoxin yield. The highest nitrate reductase activity, ATP-sulphurylase activity and xanthotoxin yield were achieved with the treatment T4. Any variation from this treatment decreased the activity of these enzymes, resulting in a reduction of the seed and xanthotoxin yield in Ammi majus L. The higher seed and xanthotoxin yield achieved in Ammi majus L. at treatment T4 could be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are influenced by S and N assimilation.