Light-dependent regulation of chlorophyll b biosynthesis in chlorophyllide a oxygenase overexpressing tobacco plants. 
Chlorophyllide a oxygenase (CAO) that converts chlorophyllide a to chlorophyllide b was overexpressed in tobacco to increase chlorophyll (Chl) b biosynthesis and alter the Chl a/b ratio.  Transgenic plants along with their wild-type cultivars were grown in low and high light intensities.  In low light there was 20% increase in chlorophyll b contents in transgenic plants, which resulted in 16% reduction in the Chl a/b ratio.  In high light, total Chl contents were 31% higher in transgenic plants than those of wild type.  The increase in Chl a was 19% and that of Chl b was 72% leading to 31% decline of Chl a/b ratio.  The increase in Chl b contents was accompanied by enhanced CAO expression that was highly pronounced in low light.  As compared to low light, in high light Lhcb1 and Chl a/b transcripts abundance was significantly increased in transgenic plants suggesting a close relationship between Chl b synthesis and cab gene expression.  However, there was a small increase in expression of LHCII proteins, which did not correspond to 72% increase in Chl b content in transgenic line, implying that LHCPII has the ability to bind more Chl b molecules.