Photophysiology of Kalanchoë Seed Germination

Abstract

The effects of irradiations with different proportions of red/farred light and of gibberellic acid on the phytochrome‐mediated seed germination of Kalanchoë blossfeldiana cv. Feuerblüte, were studied.The seed coat transmits much more red than far‐red light, and therefore the energy ratio between 660 nm and 730 nm is given only for the transmitted light. Decreasing this ratio from 65 to 1.0 caused only a very slight inhibition. If this ratio is further lowered to 0.64, a 10 min terminal irradiation after a 3‐h white light photoperiod is inhibitory, but a 12‐h photoperiod or continuous irradiation is not. If the ratio is decreased to 0.44 or 0.31, a 12‐h photoperiod is now also inhibitory, although continuous irradiation and 10 min terminal irradiation are still more inhibitory. These results are discussed in terms of phytochrome phototransformations.Although gibberellic acid is unable to cause any germination in complete darkness, it can result in a very high germination percentage, if combined with treatments which by themselves do not induce any germination such as continuous far‐red, terminal far‐red after short photoperiods, or very short photoperiods at 25°C. These results point to a strong synergism between gibberellic acid and the so‐called stabilized form of phytochrome, P*FR.

Synergism between gibberellic acid and low Pfr levels inducing germination of Kalanchoë seeds

“…The seed lots used in these experiments are much more light sensitive than those used earlier (Eidabh et al, 1974, Fredericq et al 1975, and only 2 min of WL given daily induces optimum germination on water and GA3 ( Fig. 1), In the absence of GA3, short FR irradiations revel se the effect of the preceding 2 min WL and 30 s FR is saturating.…”

“…^° increased production of gibberellins (Ikuma andThimann 1960, Scheibe andLang 1965, Hsiao and Vid-Germination oiKalanckoe seeds is absolutely light-re-aver 1973, Lewak andKhan 1977, Berrie andTaylor quiring (Bunsow andvon Bredow 1958) and phyto-1981), but this problem is not yet solved unequivocally chrome-corttrolled (Eidabh et al, 1974), Red light (Carpita and Nabors 1981), This possibility is excluded stimulates and FR inhibits germination; however, the in Kaianchoe because GA^ cannot induce germination inhibitory effect of FR disappears in the presence of in darkness, exogetious GA3 (Fredericq et al, 1975), This could be The aim of this work was to demonstrate the axisdue to a synergism between GA3 and very low Pf^levels, tence of a GA3-low Pf, synergistn in Kaianchoe and to Synergism between high P,, levels present during a investigate its characteristics and kinetics. Such a synershort period and suboptimal GA3 concentrations was gism between exogenous GA3 and low Pf, levels has not demonstrated in lettuce seeds (Bewley et al, 1967, been described.…”

PROBIT ANALYSIS OF LOW AND VERY‐LOW FLUENCE‐RESPONSES OF PHYTOCHROME‐CONTROLLED Kalanchoe blossfeldiana SEED GERMINATION*

“…(Blaauw-Jansen and Blaauw, 1975;Small etal., 1979;Blaauw-Jansen, 1983). Incubated on gibberellic acid (GA,), the seeds become very light-sensitive so that even one irradiation after a 2-day lag phase (Fredericq et al, 1975 results in a high germination response. With one irradiation of R given 7 days after sowing, the germination percentage increases gradually with increasing fluences (Fig.…”

“…Incubated on GA3S the seeds become very lightsensitive so that even a short FR irradiation results in high physiological activity (Fredericq et al, 1975;Dedonder et al, 1983). Preliminary action spectra point to phytochrome as the photoreceptor for seed germination control, both in presence and absence of GA3 (Rethy et al, 1980).…”