Storey R, Beevers L
Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019.
Plant Physiol. 1978 Apr;61(4):494-500. doi: 10.1104/pp.61.4.494.
The metabolism of glutamine in the leaf and subtended fruit of the aging pea (Pisum sativum L. cv. Burpeeana) has been studied in relation to changes in the protein, chlorophyll, and free amino acid content of each organ during ontogenesis. Glutamine synthetase [EC 6.3.1.2] activity was measured during development and senescence in each organ. Glutamate synthetase [EC 2.6.1.53] activity was followed in the pod and cotyledon during development and maturation. Maximal glutamine synthetase activity and free amino acid accumulation occurred together in the young leaf. Glutamine synthetase (in vitro) in leaf extracts greatly exceeded the requirement (in vivo) for reduced N in the organ. Glutamine synthetase activity, although declining in the senescing leaf, was sufficient (in vitro) to produce glutamine from all of the N released during protein hydrolysis (in vivo). Maximal glutamine synthetase activity in the pod was recorded 6 days after the peak accumulation of the free amino acids in this organ.In the young pod, free amino acids accumulated as glutamate synthetase activity increased. Maximal pod glutamate synthetase activity occurred simultaneously with maximal leaf glutamine synthetase activity, but 6 days prior to the corresponding maximum of glutamine synthetase in the pod. Cotyledonary glutamate synthetase activity increased during the assimilatory phase of embryo growth which coincided with the loss of protein and free amino acids from the leaf and pod; maximal activity was recorded simultaneously with maximal pod glutamine synthetase.We suggest that the activity of glutamine synthetase in the supply organs (leaf, pod) furnishes the translocated amide necessary for the N nutrition of the cotyledon. The subsequent activity of glutamate synthetase could provide a mechanism for the transfer of imported amide N to alpha amino N subsequently used in protein synthesis. In vitro measurements of enzyme activity indicate there was sufficient catalytic potential in vivo to accomplish these proposed roles.
研究了衰老豌豆（Pisum sativum L. cv. Burpeeana）叶片和所托果实中谷氨酰胺的代谢，以及各器官在个体发育过程中蛋白质、叶绿素和游离氨基酸含量的变化。在各器官的发育和衰老过程中测定了谷氨酰胺合成酶[EC 6.3.1.2]的活性。在豆荚和子叶的发育和成熟过程中跟踪了谷氨酸合成酶[EC 2.6.1.53]的活性。谷氨酰胺合成酶的最大活性和游离氨基酸的积累同时出现在幼叶中。叶片提取物中的谷氨酰胺合成酶（体外）大大超过了器官中还原态氮的需求（体内）。谷氨酰胺合成酶活性虽然在衰老叶片中下降，但（体外）足以从蛋白质水解过程中释放的所有氮（体内）产生谷氨酰胺。在该器官中游离氨基酸积累达到峰值6天后，记录到豆荚中谷氨酰胺合成酶的最大活性。在幼嫩豆荚中，随着谷氨酸合成酶活性的增加，游离氨基酸积累。豆荚谷氨酸合成酶的最大活性与叶片谷氨酰胺合成酶的最大活性同时出现，但比豆荚中相应的谷氨酰胺合成酶最大值提前6天。子叶谷氨酸合成酶活性在胚胎生长的同化阶段增加，这与叶片和豆荚中蛋白质和游离氨基酸的损失同时发生；最大活性与豆荚谷氨酰胺合成酶的最大活性同时记录。我们认为，供应器官（叶片、豆荚）中谷氨酰胺合成酶的活性为子叶的氮营养提供了转运所需的酰胺。随后谷氨酸合成酶的活性可以为将输入的酰胺氮转移到随后用于蛋白质合成的α-氨基氮提供一种机制。酶活性的体外测量表明，体内有足够的催化潜力来完成这些假定的作用。
