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Free calcium ion concentration in the sieve-tube sap of ricinus communis l. Seedlings

Title data

Brauer, Moni ; Zhong, Wen-Jun ; Jelitto, Till ; Schobert, Christian ; Sanders, Dale ; Komor, Ewald:
Free calcium ion concentration in the sieve-tube sap of ricinus communis l. Seedlings.
In: Planta. Vol. 206 (1998) Issue 1 . - pp. 103-107.
ISSN 0032-0935
DOI: https://doi.org/10.1007/s004250050379

Abstract in another language

Changes in free Ca2+ in sieve-tube sap have been proposed to be important in the regulation of phloem transport, and Ca2+-activated protein kinase activity has been described in phloem exudate (S.A. Avdiushko et al. 1997 J Plant Physiol 150: 552-559). Using atomic absorption spectrometry, we have determined that the total Ca2+ concentration in sieve-tube sap from Ricinus seedlings containing the endosperm is about 100 mu M (range 80-150 mu M). We used three independent methods to determine the free calcium ion concentration in the phloem sap ([Ca2+](p)). The first method was to calculate [Ca2+](p) from the total Ca2+ concentration, in combination with the binding constants and concentrations of the ionic solutes in phloem sap. The resultant estimate of [Ca2+](p) was 63 mu M. The second method used the Ca-specific fluorescent dye 2-[2-(5-carboxy)oxazole]-5-hydroxy-6-aminobenzofuran-N,N,-O-triacetic-acid (FURAPTRA) on exuded sieve-tube sap. Although the sap interfered severely with the fluorescence properties of the dye, Ca2+ titrations enabled a value of [Ca2+](p) = 20 mu M to be deduced. The third method used Ca2+-selective microelectrodes on exuded sap samples, which gave an average value for [Ca2+](p) = 13 mu M. No significant change in this value was observed during the sap exudation period. The Ca2+ buffer capacity was determined and the result of about 0.6 mmol.l(-1).pCa(-1) displayed excellent agreement with the measured values of free and total Ca2+ concentration in sieve-tube sap. Since the measured values for free Ca2+ are 20- to 100-fold higher than those usually reported for the cytosol of a range of plant cells in resting conditions, it is concluded that either regulation of [Ca2+](p) is of limited physiological importance, or that the Ca2+-dependent proteins respond only to relatively high [Ca2+](p). The implications for regulation of cytosolic free Ca2+ in symplastically connected companion cells is discussed.

Further data

Item Type: Article in a journal
Refereed: Yes
Additional notes: BAYCEER22486
Institutions of the University: Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology > Chair Plant Physiology
Research Institutions > Research Centres > Bayreuth Center of Ecology and Environmental Research- BayCEER
Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 500 Science
Date Deposited: 24 Sep 2015 09:38
Last Modified: 24 Sep 2015 09:38
URI: https://eref.uni-bayreuth.de/id/eprint/19725