【摘要】 用Clark型氧电极的极谱技术研究了Mg²⁺在不同光强和电子给体情况下对莴苣叶绿体（囊状体）膜的甲基紫精（MV）光还原的相对量子产量（RQY）的影响。试验结果证明:Mg²⁺在限制光强下,促进天然的以水为电子给体的MV光还原的RQY约一倍左右;而在饱和光强下促进很少;若用BD—Vit.C代替水作为PSⅡ电子给体时,Mg²⁺不论在限制光强或饱和光强下均明显地促进MV光还原的RQY,平均促进86～124％;若加DCIP—Vit.C作为PS Ⅰ电子给体时,Mg²⁺在限制光强下对MV光还原的RQY稍有抑制作用（降低25％左右）,但在饱和光强下作用减弱;若以TMPD—Vit.C代替DCIP作为PS Ⅰ电子给体,则Mg²⁺在饱和光强下明显地促进MV光还原的RQY,约增加PS Ⅰ活性两倍,但光强减弱时,刺激作用也降低。仅用满溢理论解释上述阳离子效应是很困难的,我们认为,阳离子(主要是Mg²⁺)对叶绿体囊状体膜的作用是多途径的,它的主要作用可能是在分子水平上维持天线色素、作用中心以及某些电子载体在膜上的一定构型和保持它们之间紧密关系,以保证光能高效地吸收、转化和传递。反之,若人为地掏去囊状体的阳离子,它的功能即出现严重的障碍。在掏去阳离子的囊状体膜中,从LHC到MV,可能至少有三个部位受到严重抑制或钝化,它们是:（1）抑制光能从LHC到PSⅡ作用中心的?更多还原

【Abstract】 Effects of Mg²⁺ on relative quantum yield （RQY） of methyl viologen（MV） photoreduction in lettuce chloroplast （thylakoid） membranes were investigated by using polarographic technique with Clark-type electrode, when electron donors and light intensities were changed.It has been shown that:1. When water is used as the natural electron donor the ROY of MV photoreduction under limited light intensity is nearly doubled aftes Mg²⁺ is added. But under saturated light intensity it remains almost constant.2. When benzidine （BD）-Vit. C substitutes water as PS K-specific electron donor, Mg²⁺ pronouncedly promotes the RQY of MV photoreduction by 86-124% on an average no matter how widely light intensities are changed.3. Adding DCIP-Vit. C as PS I electron donor, Mg²⁺ causes a little inhibition（～25%） of MV photoreduction under limited light condition. But the influence of Mg²⁺ decreases when light intensity is increased.4. If DCIP is substituted by TMPD as PSI electron donor, addition of Mg²⁺ increases the RQY of MV photoreduction about two-fold under saturated light, but when the light intensity becomes limited, the stimulation by Mg²⁺ decreases too.It is difficult to explain the above cation effects by spillover theory alone. We suggest that the action of cation (mainly Mg²⁺) on thylakoid membranes has multiple ways. The important function of cations may be the maintaining of a certain necessary conformation at molecular level of antenna pigments, reaction centres and some electron carriers as well as their certain closely related position in thylakoid membranes for the absorption and coversion of light energy and the electron transport at maximum efficiency. In contrast with this, if cations are depleted some thing will go wrong with the function of the membranes.It seems to us that from LHC to MV there are at least three possible sites of inhibition or inactivation in the depleted thylakoid membranes. They are: （1） the blocking of the transfer of excited energy from antenna pigments to PS Ⅱ reaction centres; （2） inactivation of PS Ⅱ reaction centres and （3） the inhibition of electron flow at a site related to PS Ⅰ.更多还原