Lucas W J
Department of Botany, University of California, Davis, California 95616.
Plant Physiol. 1979 Feb;63(2):248-54. doi: 10.1104/pp.63.2.248.
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 HCO(3) (-).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 HCO(3) (-).The influence of presence and absence of various cations on both alkaline band transport and total H(14)CO(3) (-) assimilation was examined. No specific cation requirement (mono- or divalent) was found for either process, except the previously established role of Ca(2+) at the HCO(3) (-) 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 HCO(3) (-) 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 HCO(3) (-) ion.
研究了负责在珊瑚轮藻细胞上形成碱性带的运输系统的性质。发现运输过程对外界pH不敏感，只要该值高于某个阈值。在这个阈值（pH 5.1至4.8）时，运输过程失活。通过提高外部溶液的pH值可以恢复运输功能。在外源HCO₃⁻存在的情况下总是能获得最快的恢复速率。还进行了使用10毫摩尔K⁺处理来改变质膜完整性的实验。在10毫摩尔K⁺存在的情况下，碱性带运输显著降低，但在回到0.2毫摩尔K⁺溶液后，该系统直到运输位点重新暴露于外源HCO₃⁻时才恢复。研究了各种阳离子的存在与否对碱性带运输和总¹⁴HCO₃⁻同化的影响。除了先前确定的Ca²⁺在HCO₃⁻运输位点的作用外，未发现这两个过程对特定阳离子（单价或二价）有需求。碱性带运输过程对阳离子有普遍需求。该运输系统在低阳离子溶液或玻璃蒸馏水分别中可能会部分或完全停滞。结果表明，没有阳离子通量与碱性带或HCO₃⁻运输系统直接相关地穿过质膜。认为目前的结果支持这样的假设，即OH⁻外流运输系统（而不是H⁺内流系统）负责珊瑚轮藻中碱性带的形成。结果支持OH⁻外流是一个生电过程的假设。这个OH⁻运输系统似乎还包含两个变构效应位点，涉及一个酸性基团和一个HCO₃⁻离子。
