Properties of Guard-Cell Chloroplasts and their Role in Stomatal Opening

研究了蚕豆保护细胞原生质体中Calvin-Benson循环的酶活性，利用RuBPase抗体免疫印迹法测定了保护细胞原生质体中核酮糖1,5-二磷酸羧化酶（RuBPase）的关键酶活性，并用酶偶联法和^<14>CO_2结合法测定了RuBPase的活性。所有这些测量结果表明，在叶绿素基础上，保护细胞中的RuBPase活性约为叶肉细胞的40%。其他构成Calvin-Benson循环的酶，如磷酸甘油酸激酶（PGAK）、nadp -甘油醛磷酸脱氢酶（NADP-GAPD）、三糖磷酸异构酶（TPI）、果糖双磷酸酶（FBPase）等，也在油菜保护细胞原生质中被发现。在这些酶中，与PGA/DHAP穿梭密切相关的酶具有非常高的活性，这些酶介导ATP和还原物从叶绿体向细胞质的转移，表明保护细胞非常利用穿梭。保护细胞原生质体RuBPase的叶绿素活性为叶肉原生质体的30%；而保护细胞原生质体的O_2进化速率是叶肉原生质体的3倍。不可逆NADP-GAPD在保护细胞原生质体中具有较高的活性。从这些结果中，我得出结论，保护细胞利用相当大比例的水还原等效物进行反应，而不是固定CO_2。

Enzyme activities of Calvin-Benson cycle were investigated in guard cell protoplasts from Vicia faba L. Evidence for the key enzyme of ribulose 1,5-bisphosphate carboxylase (RuBPase) was obtained in guard cell protoplasts by immunoblotting using the antibody of RuBPase, by the activity measured by methods of enzyme coupling and ^<14>CO_2 incorporation. All these measurements revealed that the activity of RuBPase in guard cells was about 40 % of that in mesophyll cells on a chlorophyll basis. Other enzymes which constitute the Calvin-Benson cycle, such as Phosphoglycerate Kinase (PGAK), NADP-glyceraldehyde phosphate dehydrogenase (NADP-GAPD), Triose Phosphate Isomerase (TPI), Fructose Bisphosphatase (FBPase) were also found in Vicia guard cell protoplasts. Among these enzymes, the enzymes related closely to the PGA/DHAP shuttle which mediate the transfer of ATP and reducing equivalents from chloroplasts to cytosol had very high activities, indicating that guard cells utilize the shuttle very largely. The RuBPase activity of guard cell protoplasts was 30% of that of mesophyll protoplasts on a chlorophyll basis; however, the O_2 evolution rate was 3 times higher in guard cell protoplasts than in mesophyll protoplasts. Irreversible NADP-GAPD was found in high activity in guard cell protoplasts. From these results I concluded that guard cells utilize a considerable proportion of reducing equivalents from water for reactions other than CO_2 fixation.