Die Steuerung des Hypokotylwachstums bei den Keimlingen vonLactuca Sativa L. durch sichtbare Strahlung

Summary

Hypocotyl lengthening of Lettuce seedlings (Lactuca sativa L., Grand Rapids, tip burn resistant strain) is barely influenced by red radiation. That, is, control of hypocotyl lengtheningvia the “reversible red, far-red system (“low energy reaction”) is negligible in these seedlings.

On the other hand, white, blue and far-red light strongly inhibit hypocotyl lengthening in these seedlings. Studies on the growth rate under various conditions of radiation and the action spectrum of the inhibition of hypocotyl lengthening by visible radiation clearly show, that hypocotyl lengthening in lettuce seedling is controlled by the “blue, far-red reaction system” (“high energy reaction”) which has been demonstrated during recent years to be involved in photomorphogenesis of plants under conditions of irradiation which are comparable with natural conditions.

The action spectrum shows strong peaks in the far-red and in the blue range of the visible spectrum. Action in the green, yellow and red part of the spectrum is negligible.

A hypothesis concerning the “high energy reaction”, recently presented byHendricks and co-workers, is critically discussed. It is shown that the hypothesis does not agree in a satisfactory way with all available experimental facts.