[The interaction of red, far-red and blue radiation in photomorphogenesis of fern gametophytes [Dryopteris filix-mas (L.) SCHOTT]].

In Fig. 1 we have reproduced the action spectrum of photomorphogenesis in fern gametophytes (Dryopteris filix-mas (L.) SCHOTT). The morphogenetic index L/W is shown as a function of wavelength (L=length, W=maximal width of the protonema). In experiments in which simultaneous irradiation with red and far-red was applied it has been shown (Fig. 2) that the effect of red light (lowering of the L/W-index) can be nullified by a simultaneous application of a suitable quantum flux density of far-red light. This fact means that the effects of red and far-red light on morphogenesis as measured by the L/W-index (Fig. 1) can be attributed exclusively to phytochrome.The strong morphogenetic effect of short wavelenth visible (=blue) light (strong lowering of the L/W-index) cannot be influenced by simultaneously applied far-red light (Fig. 4), whereas red light cancels the effect of blue light to a certain extent as measured by the L/W-index (Fig. 5). It has been concluded that the effect of blue light is due to a photoreceptor other than phytochrome, probably a flavoprotein. The antagonism between blue and red can be understood if we assume that the phytochrome-mediated growth at the tip of the apical cell of the protonema (e.g. ETZOLD, 1965) is fully promoted by P730 only at a high relative concentration of P730. The low relative concentration of P730 under far-red light is too low to counteract significantly the blue light dependent response. Blue light initiates isodiametric growth of the apical cell instead of tip growth (MOHR, 1965). Under far-red light (a low level of P730) growth of the apical cell seems to be restricted to the extreme tip of the apical cell. Slender protonemas with a high L/W-index are the result. Under red light (a high level of P730) the growing zone of the apical cell is somewhat broader. As a consequence the protonemas are broader and the L/W-index is lowered.