We have identified a mutant of pea cultivar Alaska that has many of the 
characteristics normally associated with light-grown seedlings even when grown 
in complete darkness. We have designated this mutant lip1, for light independent 
photomorphogenesis. Etiolated wild-type pea seedlings are white to slightly 
yellow in color and have a distinct morphology characterized by elongated 
epicotyls and buds containing unexpanded leaves with small, undifferentiated 
cells. In contrast, mutant seedlings grown under the same conditions are yellow 
in color and have short epicotyls and expanded leaves showing clear cellular 
differentiation. Transmission electron microscopy revealed partially developed, 
agranal plastids in the dark-grown mutant, unlike wild-type seedlings that 
contain etioplasts with prolamellar bodies. The mutant also exhibits a much 
shorter lag period for chlorophyll accumulation when etiolated seedlings are 
transferred from darkness to white light. The dark-grown mutant has 10-fold less 
spectrally detectable phytochrome, which can be attributed to a 10-fold 
reduction in the level of the PHYA polypeptide. Cab, Fed1, and RbcS transcripts 
are present in dark-grown mutant seedlings at levels comparable to those 
produced in light-grown material. The levels of these transcripts show a normal 
decrease when green plants grown for 15 days in a light/dark cycle are 
transferred to continuous darkness. However, transcript levels remain high 
during dark treatment of seedlings grown for 9 days in continuous light, 
indicating that the dark adaptation response in this mutant is developmentally 
plastic. The lip1 mutant has several features in common with the deetiolated 
Arabidopsis mutants det1, det2, and cop1. However, there are also several 
important differences, including varying effects on phytochrome levels, 
organ-specific gene expression, plastid development, and response to dark 
adaptation.