Proc. Natl. Acad. Sci. USA 74(6): 2412-2416 (June 1977)
Promotion and inhibition of flower formation in a day neutral plant in grafts with a short-day plant and a long-day plant
*MSU-ERDA Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824; and
K.A.Timiryazev Institute of Plant Physiology, Academy of Sciences of U.S.S.R., 35 Botanicheskaya ul., Moscow, U.S.S.R. 127273
Contributed by A. Lang, March 17, 1977

Flower formation in the dayneutral tobacco (Nicotiana tabacum L.) cultivar "Trapezond" was accelerated by graft union with the short-day tobacco "Maryland Mammoth" when the grafts were kept on short days and by graft union with the long-day plant N. silvestris L. when they were kept on long days. When Maryland Mammoth/Trapezond grafts were kept on long days, flower formation in Trapezond was not, or only slightly, delayed compared to Trapezond/Trapezond controls; but when N. silvestris/Trapezond grafts were kept on short days, flower formation in Trapezond was inhibited and its growth changed to dwarf-like habit. The former results indicate transmission of flower-promoting material(s) ("florigen") from photoperiodic plants maintained under flower-promoting daylength conditions to a dayneutral graft partner; the latter indicate the presence in the long-day plant N. silvestris under short-day conditions of potent flower-inhibiting and growth-regulating material(s) that can also be transmitted to a day-neutral partner. Analogous flower-inhibitory materials seem not to be present, or to be present to a much lesser extent, in the short-day plant Maryland Mammoth under long-day conditions.