Analysis of the expression of NR, AS, CS, IDH and MDH in leaves. The measurements were performed by using semi-quantitative RT-PCR method in the linear range. The seedlings were grown in a control complete nutrient solution (1) and in a control N-deprived solution (3) for 14 days. One milligramme C L−1 of HS was added for 24 h after 13 days to both +N (2) and −N solutions (4). The specific transcript levels in the y-axis of histograms (top panel) are normalized against that of the reference gene and expressed in arbitrary units (AU).