243:	Light regulation of a root-specific nitrate transporter gene, CHL1, in Arabidopsis thaliana.

Authors:	Kun-hsiang, Liu(B)Yi-fang, Tsay(A)
Affiliations:	(A): Institute of molecular biology, Academia sinica (B): Institute of life sciences, National defense Medical Center
Presenter:	Kun-hsiang, Liu , mbodie@ccvax.sinica.edu.tw

Physiological studies have shown that nitrate uptake rate displays a diurnal rhythmicity. CHL1 is a root specific, nitrate-inducible nitrate transporter involved in both low- and high-affinity nitrate uptake of Arabidopsis. In this study, we use CHL1 as a probe to examine the molecular mechanisms of the diurnal rthythmic regulation of nitrate uptake. During the day/night cycle, CHL1 mRNA showed a marked diurnal rhythmicity which increased at the end of the day and decreased at the end of the night. Light has a negative effect on the expression of CHL1 mRNA . When plants were shifted from continuous light to dark for 1.5 hours, CHL1 mRNA level increased proximately 2.5 folds. In line with this observation, when dark-adapted plants were treated with white light, CHL1 mRNA level decreased. Sucrose added in the external solution increased the expression of CHL1 mRNA. This suggests that repression of CHL1 during the day/night cycle is not due to the metabolic regulation by photosynthesis products. On the other hand, the red light pulse will cause the reduction of CHL1 mRNA. In addition, derepression of CHL1 mRNA was also observed when the root tissue was cut off from the plants before they were shifted to dark. This suggested that the root tissue (the hidden half of the plant) can response directly to light which cause the repression of CHL1 gene.