无CO_2气流中光下C_3植物叶片长时间CO_2气体交换特性研究

由于无CO_2空气中,光合CO_2固定受阻,光合环中间产物无法正常再生,以往有关无CO_2空气中C_3植物叶片CO_2猝发研究报道都是测定预光合处理的叶片迅速移入无CO_2空气中,断光后瞬间的CO_2猝发,且仅作为光呼吸强度的测定指标。在探讨无CO_2空气中C_3植物叶片光合碳代谢与光抑制相互关系时,作者观察到经光合预处理的小麦、水稻叶片,在无CO_2空气中随光暗交替,CO_2猝发可长时间进行。其强度及持续时间受氧气浓度、光强及光合产物积累量的显著影响,并受到光合能量代谢抑制剂DCMU的显著抑制。暗呼吸抑制剂碘乙酸等无明显影响。饥饿(暗处理)叶片在无CO_2空气中,CO_2猝发活性需经一定时间的光诱导方可表现。诱导过程与气孔导度变化不完全相关。诱导所需时间与光强成反比,与饥饿程度成正比。叶片光合CO_2固定以及高于2％的氧气浓度非诱导过程所必需。上述结果清楚表明:无CO_2空气中,C_3植物叶片CO_2猝发其碳源不仅来源于Calvin循环中活跃的中间产物,而且还可能经某种转化途径来源于贮藏性光合产物。本研究结果不仅揭示了无CO_2空气中C_3植物光合碳代谢的复杂性,其重要意义还在于揭示了在无CO_2空气中,甚至在相当长一段时间内,C_3植物光合碳循环并非停止,而是维持某种特殊运转。其作用可能在于通过重新动员贮藏性光合产物,“回迁”光合碳循环,参与光合机构对光抑制的适应。

CHARACTERISTICS OF CO_2 POST-ILLUMINATION BURST IN C_3 PLANT LEAVES IN CO_2-FREE GASES WITH LONG-TERM ALTERNATE LIGHT-DARK TRANSITIONS

With an IRGA, the long-term net CO_2 exchange characteristics in wheat leaves in CO_2-free air were monitored in an open system in order to explore the possible re- lationship between photosynthetic carbon metabolism in the limiting CO_2 level and photoinhibition. The prcilluminated leaf, in CO_2-free air, exhibited a long-term CO_2 postillumination burst (CO_2 PIB) which maintained for more than 1h with a substan- tial rate over the whole period or alternate light(2 min)-dark(2 min) transitions. The rate and maintaining time of CO_2 PIB, though unaffected by iodoacetic acid, were stimulated by increasing light intensity and O_2 level and were suppressed by DCMU and NEM and also were affected, to a large extent, by photosynthates loadation. For the darkened leaf, a light inductive process of CO_2 PIB was per formed accompanied by an initial undetecfable CO_2 PIB. The time requirment for light inducement of CO_2 PIB was dependent upon light intensity and the time for darkening the leaves. No close relationship between light inducement of CO_2 PIB and the corresponding change in stomatal conductance was found. The results revealed that the long-term CO_2 cvolution in CO_2-free air may be derived not only directly from the intermediates in Calvin cycle, but from leaves's reserves of reduced carbon via an uncertain mechanism, which probably exerts an important role in coordination of carbon and energy metabolism during photosynthesis in C_3 plants under the condition of photoinhibition.