Phytochrome Action during Prechilling Induced Germination of Betula papyrifera Marsh

Abstract

Seeds of paper birch (Betula papyrifera Marsh.) were induced to germinate by prechilling at 3 C or by red light. The light requirement was mediated by phytochrome and the action of phytochrome during prechilling was investigated. Red irradiation (R) prior to prechilling markedly enhanced the effectiveness of the prechilling treatment in inducing subsequent germination at 18 C. Reversal of this enhancement by far-red irradiation (FR) was more effective when FR was supplied after a 1-week prechiUl treatment than after a 2-week treatment. The R enhancement effect exhibited a sharp drop as prechilling temperature was increased from 5 to 7 C. This decline is consistent with a membrane phase transition at about 7 C where Pfr action is diminished by a loss in sensitivity of its receptor sites. Although phytochrome action was observed during prechillng treatments, the seeds failed to germinate at prechilling temperatures. Therefore, it was concluded that while potentiation of germination by Pfr occurred during prechiling, some other reaction(s) leading to radicle protrusion requires higher temperatures. In one seed source loss of germination potential was observed with protracted storage at 3 C. This was prevented by R supplied during the prechiling treatment. Taken colectively the data suggest that action of phytochrome during prechilling is accentuated in these seeds by two factors: (a) an increase in the sensitivity (or number) of Pfr receptor sites; and (b) preservation of Pfr by deferment of thermal reversion.

Biphasic Fluence-Response Curves for Phytochrome-Mediated Kalanchoë Seed Germination

“…In phytochrome-mediated seed germination, shifts from a LF response to a VLF plus LF response were obtained with high and low temperature treatments (1,3,4,14,19,24,(26)(27)(28) and ethanol treatment (26,27 (6).…”

“…Assuming that there is a logarithmic normal distribution of D requirement in the responding seed population fraction around a mean level of D required for half-maximal response, the sigmoid dose-response curves can be linearized by means of probit transformation of the germination response (9,12). The equation of the straight line in the probit diagram is defined as the LDP equation Y=5+jlog[D]-mlB (1) where Y is the probit of the germination percentage, m = log g with ,u the mean of the distribution or dose for half-maximal response and the slope B = I/a with a the standard deviation of log D around u. Similar statistical appraoches have been previously employed (5,10,14,25), but they assumed a logarithmic normal distribution of Pfr requirement of the individuals in the seed population around a mean level of Pfr required for 50% germination, instead of half-maximal germination used in this paper.…”

Stem Extension Rate in Light-Grown Plants

“…rhythm in SER after thermal stimulation should therefore be itinuous Light at 24C. due to a decrease in sensitivity to light promoted by changes in 40C with 12 h at 10°C, interactions between photoreceptors and membrane receptor B) was the same as after sites (1,19,20) during the 10 h following the low temperature (Fig. 5A) "Introduction").…”

Reservoir de graines des sols de sapinieres boreales au nord du Lac Saint-Jean

“…Par la suite, elles ont été entreposées à la noirceur dans des vials de verre à une température variant entre 1 et 4°C pour ne pas stimuler la levée de dormance (Bevington et Hoyle, 1981;Baskin et Baskin, 1990. La durée de l'entreposage a varié de 2 à 6 mois pour les sols récoltés en 1991 et de 1 à 2 mois pour les sols récoltés en 1992.…”

“…Les graines de cette espèce germent lorsqu'elles sont exposées à la lumière (Bevington et Hoyle, 1981;Bevington, 1986) et il est typique de constater son apparition dans les coupes (Marks, 1974;Grime, 1979). La germination de Betula papyrifera s'observe sur le terrain par des pourcentages de recouvrement élevés des strates arbustives et herbacées dans les parcelles perturbées, alors qu'ils sont faibles ou nuls dans les parcelles non perturbées (tableau 1).…”