Phytochrome-mediated light regulation of nitrate reductase expression in squash cotyledons.

In etiolated squash (Cucurbita maxima L.) cotyledons, nitrate-inducible NADH:nitrate reductase activity and protein were increased in darkness by red light pulses with red/far-red photoreversibility. Continuous far-red light also led to increased levels of nitrate reductase activity and protein. Poly(A)+RNA, which hybridizes to squash nitrate reductase cDNA, was also increased by light treatments. Thus, we found that after nitrate triggering, nitrate reductase expression appears to be regulated by light via phytochrome.