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PHOTOPHYSIOLOGY OF TURION GERMINATION IN Spirodela polyrhiza (L.) SCHLEIDEN–V. DEMONSTRATION OF A CALCIUM‐REQUIRING PHASE DURING PHYTOCHROME‐MEDIATED GERMINATION
Author(s) -
Appenroth K.J.,
Augsten H.
Publication year - 1990
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1990.tb01756.x
Subject(s) - phytochrome , germination , calcium , etiolation , reversion , phase (matter) , botany , biophysics , biology , irradiation , pulse (music) , red light , chemistry , optics , biochemistry , physics , organic chemistry , detector , gene , nuclear physics , phenotype , enzyme
— Etiolated turions of Spirodela polyrhiza are positively photoblastic and show a phytochrome‐mediated low fiuence germination response. The far‐red light (FR) reversibility decreased with the delay of FR irradiation (lag phase 1.06 ± 0.03 days after red light irradiation; half‐maximal response 1.9 days). The action of the far‐red‐absorbing form of phytochrome (Pfr) was only realized by a germination response if exogenously applied Ca 2 + was present. Calcium step‐down (from 1 mM to 0.9 μ M Ca 2 +) and Ca 2 + step‐up (from 0.9 μ M to 1 m M Ca 2 +) experiments were carried out to determine the Ca 2 +‐sensitive phase. There was no time gap between the two phases determined by the step‐down and step‐up experiments but a clear coincidence of both curves. Pulse treatments (24 h) with Ca 2 + (1 m M ) showed the upper part of this common curve to represent the most Ca 2 +‐sensitive phase. The Ca 2 +‐sensitive phase was within the Pfr‐requiring phase. After reversion of Pfr by FR pulses there was only a negligible response to the high Ca 2 +‐concentration, independent of the delay between the red light (R) and FR pulses. These results are compatible with the assumption of Ca 2 + acting as a second messenger of Pfr. However, the Ca 2 +‐insensitivity in the first 12 h after the R pulse points against this hypothesis.