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. Although, GA₃ and KNO₃ modulate VLF and LF, respectively, there is no direct influence on the phytochrome-phototransformations. Once P_fr is formed (in VLF or LF, or preserved in dry seeds) germination is proportional to the GA_S concentration (for VLF and dark germination) or proportional to the KNO, concentration (for LF). The non-photochemical events leading to germination seem to be triggered by a similar action mechanism for both GA, and KNO₃.