title: The action spectrum for maximal photosensitivity of germination.
abstract: Fruits of Garden Lettuce, imbibed in 0.01 M KNO3, were depleted of maternal active phytochrome B by saturating deep-red exposure and photosensitized by chilling for 1 week at 4 degrees C. Twenty saturated fluence-response curves for photoinduced germination were elaborated between 300 and 800 nm, using exposure periods from 6 to 600 s at 22.5 degrees C; there is linear and closely parallel regression in the logarithmic probability net. The reciprocals of the half-response fluences obtained gave the apparent conversion spectrum of the controlling pigments and this was corrected for the transmittance of the seed-coat. It is a phytochrome spectrum of Pr with photoconversion cross-sections of 1.2 x 10(9) and 4.5 x 10(3) m2 mol-1 at 666 and 800 nm, respectively. This means that for half-saturated germination of sensitized seed, fewer than 1 out of 200,000 phytochrome A molecules have to be photoconverted to Pfr, and no photo-reversibility by deep-red was found. Therefore, all spectral colours of nightly moon- or skylight should stimulate the germination of sensitized weed seeds if they are exposed at the soil surface between sequential tillage operations.
authors.affiliation: Universität Erlangen-Nürnberg, Institut für Botanik I, Germany. karl.hartmann@rzmail.uni-erlangen.de
authors.forename: K M
authors.initials: KM
authors.lastname: Hartmann
authors.forename: A
authors.initials: A
authors.lastname: Mollwo
mesh_terms: D019659:Asteraceae / Q000502:physiology* / Q000528:radiation effects; D010786:Photoreceptor Cells; D010834:Phytochrome / Q000378:metabolism; D051939:Phytochrome B; D012639:Seeds / Q000502:physiology* / Q000528:radiation effects; D013472:Sunlight; D014157:Transcription Factors
chemical_list: D014157:Transcription Factors; D010834:Phytochrome; D051939:Phytochrome B