Analysis of the Effect of Light and Temperature on the Fluence Response Curves for Germination of Rumex obtusifolius

Abstract

Both red light (10 minutes) and 35°C treatment (60 minutes) stimulate the germination of seeds of Rumex obtusifolius otherwise maintained in darkness at 25°C. Fluence response curves were determined for the effect of red light to stimulate germination of seeds with and without 35°C treatment. The endogenous far-red absorbing form (Pfr) level in the seeds was determined using short saturating fluences of wavelengths of light which maintain different proportions of phytochrome as Pfr at equilibrium. In the seed batches investigated, the endogenous Pfr level was found to be 4% or less of the total phytochrome. High dark germination after 35°C treatment does not result from an increase in sensitivity of the whole population to Pfr. Calculated fluence response curves for germination which best fit the experimental data suggest that seeds germinate in darkness after 35°C treatment because of a nonphytochrome-related process (overriding factor).The involvement of phytochrome in the germination of Rumex obtusifolius has been demonstrated by several authors (7,15,24). At 25°C seeds of R. obtusifolius contain a concentration of Pfr below the threshold necessary to stimulate germination. A single (R3) irradiation induces germination by photoconversion of Pr to Pfr (15). However, alternating low and high temperature can induce germination in darkness (7,22). Isikawa and Fujii (15) (19) observed that light-requiring lettuce seeds respond to high temperature in the same way as R. obtusifolius. They also showed broadband FR can partially reverse the induction of germination brought about by the high temperature treatment and concluded that this was due to the reduction of preexisting Pfr to which the seed population had become sensitive.This paper reports detailed fluence response curves for induction of germination of three seed batches of R. obtusifolius by R with or without a short 35°C treatment and estimates of their preexisting Pfr content. Four hundred seeds were sown on four layers of filter paper (Ederol Nr 15, W. Germany) moistened with 4 ml distilled H20 in a 5-cm plastic Petri dish, and incubated in darkness at 25C. All treatments were given after 24 h from sowing when maximum sensitivity to both light and 35°C treatment is attained (18). In determining fluence response curves all fluences were given in 60 s using a custom built projector with a 250-w quartz iodine lamp in combination with an interference filter, (660 nm), bandwidth at 50% transmission 10 nm (Balzers, B40 type, Liechtenstein) in combination with neutral glass filters (NG., Schott u. Gen., Mainz., W. Germany). Different MATERIALS AND METHODS

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