Photoreceptive sites in the photocontrol of oat seedling growth

The influence of red light on the growth of coleoptiles and mesocotyles of etiolated and pre-irradiated oat seedlings was investigated. Red light (15 min.) applied on whole seedlings stimulated the elongation of coleoptiles and inhibited the growth of mesocotyles both in etiolated and in pre-irradiated plants. Irradiation with red light (2 min) of various 2-mm-long regions of etiolated and pre-irradiated oat seedlings was carried out in order to locate their light reception regions. On the basis of growth reactions after such treatment it was found that in completely etiolated seedlings the light reception sites involved in the stimulation of coleoptile elongation and inhibition of mesocotyle growth lie directly above and below the seedling node, whereas in pre-irradiated seedlings, in the top of the seedling. These results point to the existence of different growth photoregulation systems in etiolated and pre-irradiated oat seedlings. The role of phytochrome in these phenomena is discussed.