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

对蚕豆保卫细胞原生质体中的Calvin-Benson循环酶活性进行了研究。用RuBPase抗体进行免疫印迹，通过酶偶联和~(14)&gt；CO_2掺入的方法，对保卫细胞原生质体中的核酮糖1，5-二磷酸羧基酶(RuBPase)的活性进行了研究。这些结果表明，保卫细胞中RuBPase的活性约为叶肉细胞中的40%。组成Calvin-Benson循环的其他酶，如磷酸甘油酸激酶(PGAK)、NADP-甘油醛磷酸脱氢酶(NADP-GAPD)、磷酸三糖异构酶(TPI)、果糖二磷酸酶(FBPase)也存在于蚕豆保卫细胞原生质体中。在这些酶中，与PGA/DHAP穿梭密切相关的酶具有很高的活性，表明保卫细胞非常大量地利用穿梭。PGA/DHAP穿梭介导ATP的转移和叶绿体到细胞质的还原当量。保卫细胞原生质体的RuBPase活性是叶肉原生质体的30%，但保卫细胞原生质体的放氧速率是叶肉原生质体的3倍。在保卫细胞原生质体中发现不可逆的NADP-GAPD高活性。根据这些结果，我得出结论，保卫细胞利用水中相当大比例的还原当量进行反应，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.