Photophysiology of Turion Germination in Spirodela polyrhiza (L. ) SCHLEIDEN. Iv. Importance of Calcium and Calmodulin

Komusiewicz

Hertel

et al. 1991

Planta

Red-light-induced germination (via phytochrome) of turions of Spirodela polyrhiza (L.) Schleiden, strain SJ, showed an absolute requirement for exogenously applied calcium (Appenroth et al. 1990b, Biochem. Physiol. Pflanzen 186, 209-219). With calcium step-up experiments (from 0.9 μM to 1 mM Ca(2+)) the influence of Ca(2+) on the escape from far-red-light reversibility was investigated. Delaying the time of Ca(2+) application after the red light pulse resulted in an increased reversibility. This confirmed that the calcium-requiring phase is within the phytochrome-dependent period. Ten days after a red light pulse was applied the activity of β-amylase (EC 3.2.1.2) was increased about tenfold. The starting point was similar in the germination and enzymatic responses, but half-maximal response times according to the Mitscherlich function (2.5 d and 6.9 d, respectively) and times of saturation (about 6 d and 9 d, respectively) were different. Increase of β-amylase activity was completely inhibited by irradiation with far-red light (demonstrating phytochrome as the photoreceptor), as well as by inhibitors of translation (cycloheximide, puromycin) and transcription (cordycepin). Once formed, the active enzyme protein was stable for at least 4 d after cycloheximide application. After application of cordycepin a small amount of translation activity was detected until complete inhibition was reached after 2 d. This phytochrome-modulated, de-novo synthesis of β-amylase was only slightly dependent on exogenous Ca(2+). Therefore, it can be concluded that the phytochrome-mediated signal-transduction chain branches either in its reversible part or as a consequence of diversity of the primary phytochrome reaction.

Section: Materials and Methods)mentioning

confidence: 98%

Section: Materials and Methods)mentioning

confidence: 99%

Section: Materials and Methods)mentioning

confidence: 99%

Section: Cultivation and Germination Cultivation Of The Great Duckweedmentioning

confidence: 99%

Section: Is There a Calcium-requirin9 Step In The Phytochromedependenmentioning

confidence: 99%

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Photophysiology of turion germination in Spirodela polyrhiza (L.) Schleiden VIII. Calcium dependence and ?-amylase activity

Komusiewicz

Hertel

et al. 1991

Planta

Die Vielwurzelige Teichlinse. Ohne Stickstoff „geht nichts”︁

Biologie in unserer Zeit

1993

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Ion antagonism in phytochrome-mediated calcium-dependent germination of turions of Spirodela polyrhiza (L.) Schleiden

Gabryś

Scheuerlein

1999

Planta

Self Cite

The light-dependent germination response of turions (resting fronds) is mediated by phytochrome and requires the presence of Ca 2+ in the medium (K.-J. Appenroth and H. Augsten, 1990, Photochem. Photobiol. 52: 61±65). The Ca 2+ requirement of germination is apparent only in the presence of exogenous Mg 2+ . A competitive ion antagonism was demonstrated between Ca 2+ and Mg 2+ in this physiological response; Mg 2+ could also be replaced by Ba 2+ or Sr 2+ . Without exogenous Mg 2+ , a Ca 2+ concentration as low as 0.9 lM ful®lled the Ca 2+ requirement. This type of ion antagonism resembled the competitive Ca/Mg interaction reported previously for calcium-binding proteins. The physiological response was blocked by inhibitors of Ca 2+ uptake (verapamil, La 3+ ). It was concluded that uptake of Ca 2+ from the external medium is an essential step in the phytochrome-mediated germination of turions. The results are in agreement with the assumption that the uptake of Ca 2+ is blocked at the side of entry by other alkaline earth ions. Treatment of turions with Mg 2+ (1 mM) for 24 h at varying times after the red light pulse in otherwise virtually Ca 2+ -free KNO 3 solution resulted in a response similar to a Ca 2+ stepdown treatment. This is in agreement with the assumption that the Ca 2+ -and the Mg 2+ -sensitive periods coincide. The ion interaction described here represents the ®rst photophysiological example in plants of an antagonistic eect between Ca 2+ and Mg 2+ similar to that which occurs in vitro with calmodulin.