Department of Horticulture, University of Wisconsin, Madison, Wisconsin 53706.
Plant Physiol. 1982 Aug;70(2):616-25. doi: 10.1104/pp.70.2.616.
The leaf anatomy and certain photosynthetic properties of nitrate- and ammonia-grown plants of Moricandia arvensis (L.) DC., a species previously reported to be a C(3)-C(4) intermediate, were investigated. Nitrate-grown plants had a high level of malate in the leaves while ammonia-grown plants had low levels of malate. In young leaves of nitrate-grown plants, there was a diurnal fluctuation of malate content, increasing during the day and decreasing during the night. Titratable acidity remained low in leaves of both nitrate- and ammonia-grown plants.In nitrate-grown plants, the activity of phosphoenolpyruvate (PEP) carboxylase was about 2-fold higher than in ammonia-grown plants, the latter having activity typical of C(3) species. Also, in nitrate-grown plants, the ratio of activities of ribulose 1,5-bisphosphate (RuBP) carboxylase/PEP carboxylase was lower than in ammonia-grown plants. Nitrate reductase activities were higher in nitrate- than in ammonia-grown plants and the greatest activity was found in younger leaves.With nitrate-grown plants, during a pulse-chase experiment the label in malate, as a percentage of the total labeled products, increased from about 7% after a 10-second pulse with (14)CO(2) up to 17% during a 5-minute chase with (12)CO(2). The pattern of (14)C labeling in various metabolites suggests the primary carboxylation is through RuBP carboxylase with a secondary carboxylation through PEP carboxylase. In similar experiments, with ammonia-grown plants, the percentage label in malate was only 0% to 4% with no increase in malate labeling during the chase period. The CO(2) compensation point was lower in nitrate-grown than ammonia-grown plants.There was no evidence of Kranz-like anatomy in either the nitrate or ammonia-grown plants. Mitochondria of bundle-sheath cells were strikingly positioned along the inner tangential wall. This might allow the chloroplasts of these cells to fix the mitochondrial photorespired CO(2) more effectively and contribute to the low CO(2) compensation point in the species. Chloroplasts of bundle-sheath cells and contiguous mesophyll cells were similar in size and structure in plants grown on different media, although chloroplast thylakoids and stromata of the ammonia-grown plants stained more intensely than those of nitrate-grown plants. In addition, irregular clusters of phytoferritin particles occurred in the chloroplasts of the ammonia-grown plants.The results indicate that the substantial activity of PEP carboxylase, incorporation of CO(2) into malate, the high malate content, and in part the relatively low CO(2) compensation point in Moricandia arvensis may be accounted for by metabolism of nitrate rather than by a state of C(3)-C(4) intermediacy.
研究了先前报道为 C(3)-C(4)中间型的 Moricandia arvensis(L.)DC. 的硝酸盐和氨培养植物的叶片解剖结构和某些光合作用特性。硝酸盐培养的植物叶片中有高水平的苹果酸,而氨培养的植物叶片中苹果酸水平较低。在硝酸盐培养的植物的幼叶中,苹果酸含量存在昼夜波动,白天增加,晚上减少。无论是在硝酸盐培养的植物还是氨培养的植物中,可滴定酸度都保持在低水平。在硝酸盐培养的植物中,磷酸烯醇丙酮酸(PEP)羧化酶的活性比氨培养的植物高约 2 倍,后者具有 C(3) 物种的典型活性。此外,在硝酸盐培养的植物中,核酮糖 1,5-二磷酸(RuBP)羧化酶/PEP 羧化酶的活性比氨培养的植物低。硝酸盐还原酶的活性在硝酸盐培养的植物中高于氨培养的植物,并且在较年轻的叶片中发现了最大的活性。在硝酸盐培养的植物中,在脉冲-追踪实验中,用 (14)CO(2)进行 10 秒脉冲后,标记在苹果酸中的百分比(以总标记产物的百分比计)从约 7%增加到用 (12)CO(2)进行 5 分钟追踪时的 17%。在各种代谢物中(14)C 标记的模式表明,初级羧化是通过 RuBP 羧化酶进行的,次级羧化是通过 PEP 羧化酶进行的。在类似的实验中,用氨培养的植物,标记在苹果酸中的百分比仅为 0%至 4%,并且在追踪期间苹果酸标记没有增加。与氨培养的植物相比,硝酸盐培养的植物的 CO(2)补偿点较低。在硝酸盐或氨培养的植物中都没有出现 Kranz 样解剖结构的证据。束鞘细胞的线粒体沿着内切线壁排列得非常明显。这可能使这些细胞的叶绿体更有效地固定线粒体光呼吸产生的 CO(2),并有助于该物种的低 CO(2)补偿点。在不同培养基上生长的植物中,束鞘细胞的叶绿体和相邻的叶肉细胞的叶绿体大小和结构相似,尽管氨培养的植物的叶绿体类囊体和基质比硝酸盐培养的植物染色更深。此外,在氨培养的植物的叶绿体中还出现了不规则的类植物铁蛋白颗粒簇。结果表明,Moricandia arvensis 中 PEP 羧化酶的大量活性、苹果酸中 CO(2)的掺入、苹果酸含量高以及部分 CO(2)补偿点相对较低,可能归因于硝酸盐的代谢,而不是 C(3)-C(4)中间型状态。