H. Fredericq

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

Abstract— Kalanchoë blossfeldiana seeds are light‐requiring for seed germination. On water or KNO3 solution and irradiated with several daily red (R) irradiations, the seeds show a low‐fluence (LF) response which is far‐red (FR) reversible. Incubated on gibberellic acid (GA3) the seeds show a very‐low‐fluence (VLF) response which can be saturated with red as well as with far red light. As germination is a quantal response, the sub‐optimal segments of the dose‐response curves are analysed by means of probit analysis in order to calculate the seed population parameters. There is a linear relation between the probit of the germination response and the logarithm of the fluence. Moreover, the slope for the VLF as well as for the LF response is the same. The VLF requires about 8 × 104 times less fluence than the LF. VLF saturation with FR requires about 200 times more fluence than with R.

Photomorphogenesis and Hormones

This review is restricted to phytochrome-mediated light effects and to the generally recogniz’d five classes of natural hormones, auxins, gibberellins, cytokinins, abscisic acid and ethylene. Other environmental conditions having morphogenic effects in relation to phytochrome and hormone actions are included when they are relevant to our objective. Aspects of flower induction are mentioned when an interaction between phytohormones and phytochrome is evident.

Enhancement of senescence by far-red light.

SummaryFar-red light was demonstrated to accelerate senescence in mature, green tissue of intact thalli of Marchantia polymorpha. The red/far-red reversibility of this phenomenon proves the involvement of phytochrome. As a daily exposure to 5 min red light is sufficient to prevent aging of the tissue, photosynthesis does not play a specific role in this response.

ENERGY METABOLISM OF IMBIBING KALANCHOË SEEDS. RESPONSE TO GIBBERELLIC ACID AND CONTRIBUTION OF RESPIRATION AND FERMENTATION TO ATP PRODUCTION

In Kalanchoe blossfeldiana seeds imbibed in the dark for 10 days at 20°C, very similar energy charge ( EC ) values were measured in the presence and absence of gibberellic acid (GA 3 ). This demonstrates that GA 3 does not prevent or strongly delay the induction of secondary dormancy in Kalanchoe seeds by elevating EC levels. However, GA 3 clearly increased the ATP and AMP content of the seeds. During the first hours of anoxic imbibition, the sodium-fluoride sensitive ATP production still represents 25 to 30% of the ATP amount produced in the air, indicating that in Kalanchoe seeds the fermentative pathway can partly contribute to ATP production. As the oxygen uptake by the seeds is cyanide-sensitive and a severe inhibition of the increase in ATP content by cyanide can be demonstrated during the first hours of aerobic imbibition, our results indicate the participation of the normal cytochromic pathway in ATP synthesis.

Factors Eliciting the Germination of Photoblastic Kalanchoe Seeds

In the Series “Monographies de Physiologie Vegetale” edited by professor P.E. Pilet of the University of Lausanne, Switzerland, Daniel Come (1970) wrote in the introductory remarks of his book “Les Obstacles a la Germination” : “… si l’on connait le plus souvent les causes essentielles de la non-germination d’une semence, et si l’on sait quels traitements appliquer a cette semence pour la rendre apte a germer, les raisons profondes de la non-germination sont les plus souvent inconnues ou seulement tres partiellement connues. Les recherches actuelles s’orientent progressivement vers une meilleure comprehension de ces mecanismes. L’experimentation est difficile du fait que le repos des semences ne correspond pas a un simple arret de croissance et que la germination elle-meme est encore un phenomene assez mal connu.”