Ein Wirkungsspektrum der Photomorphogenese unter Hochenergiebedingungen und seine Interpretation auf der Basis des Phytochroms (Hypokotylwachstumshemmung bei Lactuca sativa L.)

Abstract

Control by ligth of hypocotyl lengthening in lettuce seedlings (Lactuca sativa L., cv. Grand Rapids, tip burn resistant strain) has been investigated using high quality monochromatic bands of radiation between 320 and 1100 nm wave length. Continuous irradiation was applied between 54 and 72 hours after sowing. The increase of hypocotyl length during this period was measured. — A set of characteristic dose-response-curves is presented. For the calculation of the action spectrum — relative quantum efficiency (N 447 nm /N λ ) as a function of wave length — the branches of the dose-response-curves between 60 and 80% increase were used. The action spectrum shows a symmetric peak around λ = 716 nm with a band width of 30 nm. This fact agrees with the conclusion 1 that the far-red peak of action in the case of long-time irradiation is exclusively due to phytochrome. The photostationary state [P fr ] / [P] for optimum effectiveness with respect to control of hypocotyl lengthening in lettuce is probably around 3%. — The fine structure of the action spectrum in the blue and ultraviolet range (especially the peak around λ= 363 nm) points to a flavoproteid as the photoreceptor. On the other hand it is well known 1 that with long-time irradiation short wavelengths light as well will maintain photostationary states of the phytochrome system. Further experiments are required to solve the problem of how much of the effect of blue and ultra-violet light can be attributed to phytochrome.