The induction of flowering in mustard (Sinapis alba L.) was studied by means of night-breaks (" StSrlicht"). The plants were cultivated under fully controlled conditions : 8000 Lux white light (mixed fluorescent and incandescent) 18 ~ C, 80% relative humidity. Raised under our conditions in short days (8 hours of white light) mustard behaved as a quantitative long-day plant (Fig. 2). Flowering can be promoted by long-day treatment (Fig. 3). The long day (16 hours of white light) can be replaced by a short day plus a night-break. The highest effectiveness of the night-break is found near the middle of the dark period (Figs. 4, 5). --The spectral dependence of flower induction was studied with blue, green, yellow, red (Fig. 1) and far-red light using a 2-hour break near the middle of the dark period. The dose response curves (Fig. 6) and the action spectrum (Fig. 7) indicate a very strong effec'~iveness irt the blue part of the spectrum, a small response in red and yellow light and no response at all in green and far-red light. The participation of phytochrome is indicated (Table 1), but no far-red reversibility could be detected (Table 2). Simultaneous irradiation with red and far-red light yielded significant enhancement effects (Fig. 8). In view of the strong shadoudng in the leaves (Figs. 9, 10) these data are interpretable on the basis of phytochrome.
Einleitung
Nach den U n t e r s u c h u n g e n von BEI~NIEIa (1963, 1964) handelt es sich bei Sinapis alba L. bezfiglieh der photoperiodisehen Reaktion u m eine obligatorisehe Langtagpflanze (LTP). Die kritisehe Tagesl/~nge soll etwas u n t e r h a l b yon 10 Std liegen. U n t e r geeigneten Bedingungen ist ffir eine Blfihinduktion lediglieh ein photoperiodischer Cyelus erforderlieh. Neuere U n t e r s u c h u n g e n h a b e n gezeigt, dab bei relativ hohen Liehtintensit/tten wahrend der Hauptliehtperiode Sinapis alba L. als fakultative Langtagpflanze reagieren k a n n (BouILLENNE U. Mitarb., zit. naeh BERNIER, 1968). Dieses Verhalten zeigen aueh die yon uns verwendeten Senfpflanzen.