Using Arabidopsis thaliana, two scientists at the Scripps Research Institute (TSRI) have demonstrated for the first time that plants use two sets of proteins to detect daylight levels that in turn trigger the flowering response. Like solar-powered clocks, two photoreceptor proteins (the blue light photoreceptor "cryptochrome" and the red light photoreceptor "phytochrome") are activated when exposed to daylight and transported to the nucleus of the plant cells where they alter the expression of a number of genes. As the sun varies throughout the day, the number and ratio of cryptochromes and phytochromes that are reaching the nucleus varies and these changes allow them to delicately control many other genes. One gene that is influenced encodes a protein called "Constans" that triggers the flowering of the plant but only when the right number and ratio of the two photoreceptors molecules is reached. The discovery opens up many possibilities in ornamental horticulture and also in boosting food production by manipulating day length sensitivity and increasing our capacity to grow crops efficiently at different latitudes at different times of the year. Keith McKeown E-mail: kmckeown@scripps.edu