Photomorphogenesis in Impatiens Parviflora and Other Plant Species Under Simulated Natural Canopy Radiations

S ummary Nitrate reductase activity in the leaves of Sinapis alba L. and Chenopodium album L. was found to be related to the photoequilibrium of phytochrome established under simulated natural canopy radiation (fluorescent white light with added far‐red light) of a relatively high photon fluence rate. Under simulated canopy radiation of low photon fluence rate, more characteristic of ‘shade’ light, the degree of responsiveness of S. alba nitrate reductase has been seen to be reduced. However, in the leaves of Impatiens parviflora L., a species frequently occurring in dense canopy shade, nitrate reductase activity showed a rapid and marked response to changes in phytochrome photoequilibrium with the low‐fluence rate sources. Under these same conditions the elongation growth of I. parviflora internodes also showed a marked and rapid response to changes in the phytochrome system, rather than displaying a reduced response as has been proposed for shade tolerating species.