Abstract
The nature of the transport system responsible for the establishment of alkaline bands on cells of Chara corallina was investigated. The transport process was found to be insensitive to external pH, provided the value was above a certain threshold. At this threshold (pH 5.1 to 4.8) the transport process was inactivated. Transport function could be recovered by raising the pH value of the external solution. The fastest rate of recovery was always obtained in the presence of exogenous HCO3−.
Experiments in which plasmalemma integrity was modified using 10 millimolar K+ treatment were also performed. Alkaline band transport was significantly reduced in the presence of 10 millimolar K+, but the system did not recover, following return to 0.2 millimolar K+ solutions, until the transport site was reexposed to exogenous HCO3−.
The influence of presence and absence of various cations on both alkaline band transport and total H14CO3− assimilation was examined. No specific cation requirement (mono- or divalent) was found for either process, except the previously established role of Ca2+ at the HCO3− transport site. The alkaline band transport process exhibited a general requirement for cations. This transport system could be partially or completely stalled in low cation solutions, or glass-distilled water, respectively. The results indicate that no cationic flux occurs across the plasmalemma in direct association with either the alkaline band or HCO3− transport systems.
It is felt that the present results offer support for the hypothesis that an OH− efflux transport system (rather than a H+ influx system) is responsible for alkaline band development in C. corallina. The results support the hypothesis that OH− efflux is an electrogenic process. This OH− transport system also appears to contain two allosteric effector sites, involving an acidic group and a HCO3− ion.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Kitasato H. The influence of H+ on the membrane potential and ion fluxes of Nitella. J Gen Physiol. 1968 Jul;52(1):60–87. doi: 10.1085/jgp.52.1.60. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lucas W. J., Dainty J. HCO(3) Influx Across the Plasmalemma of Chara corallina: Divalent Cation Requirement. Plant Physiol. 1977 Dec;60(6):862–867. doi: 10.1104/pp.60.6.862. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lucas W. J. HCO(3) Influx across the Plasmalemma of Chara corallina: Physiological and Biophysical Influence of 10 mm K. Plant Physiol. 1978 Apr;61(4):487–493. doi: 10.1104/pp.61.4.487. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Richards J. L., Hope A. B. The role of protons in determining membrane electrical characteristics in Chara corallina. J Membr Biol. 1974;16(2):121–144. doi: 10.1007/BF01872410. [DOI] [PubMed] [Google Scholar]
- Spanswick R. M. Evidence for an electrogenic ion pump in Nitella translucens. I. The effects of pH, K + , Na + , light and temperature on the membrane potential and resistance. Biochim Biophys Acta. 1972 Oct 23;288(1):73–89. doi: 10.1016/0005-2736(72)90224-6. [DOI] [PubMed] [Google Scholar]
- Spear D. G., Barr J. K., Barr C. E. Localization of hydrogen ion and chloride ion fluxes in Nitella. J Gen Physiol. 1969 Sep;54(3):397–414. doi: 10.1085/jgp.54.3.397. [DOI] [PMC free article] [PubMed] [Google Scholar]