Bulletin Spring‧Summer 2001

Screening for ASN1 homozygous transgenic plants. When grown on selection medium, untransformed plants turn yellow while transformed plants stay green. discovered tha t under both ligh t and dark conditions, the ASN 1 gene in these transgenic lines is very active, producin g high amounts of mRNA and asparagine synthetase, which subsequently causes a sharp increase in the l e v el o f free asparagine i n leaves. In comparison, the ASN 1 gene in the control plants expresses strongly only in the dark. T h i s is be c au s e , i n the absence o f photosynthesis, the plants, to prevent wastage, catalyzes asparagine to stor e nitrogen temporarily. Coinciding with Traditional Cultivation Model Sc i en t i s t s have used e l eva t ed AS activities and asparagine levels in leaves as parametres to screen fo r high grain protei n in maize and rye. One purpose of Prof. Lam's research is to i d e n t i fy the relationship between asparagine level i n leaves and protein level in seeds. The researchers observed that in ASN 1 overexpressing lines, there is a significant increase in the level of free asparagine not only in leaves, but also in green siliques (fruits). However, in both transgenic plants and in normal , wild-type plants, the free amino acid content in seeds is found to be much lower than that in leaves or siliques. This suggests that during seed development, nitrogen resources w i l l be transported from Elevation of the ASN mRNA levels in ASN overexpressing lines — L: light-grown plants; D: dark-adapted plants. Significant increase in seed nitroge n content in ASN1 overexpressing lines as compared to the controls, (*, P<0.05) Chinese University Bulletin Spring • Summer 2001 32