Magnesium deficiency–induced impairment of photosynthesis in leaves of fruiting Citrus reticulata trees accompanied by up‐regulation of antioxidant metabolism to avoid photo‐oxidative damage

Limited data are available on the physiological responses of leaves from fruiting trees to magnesium (Mg) deficiency. Magnesium deficiency–induced effects on photosystem II (PSII) photochemistry in leaves of fruiting (Citrus reticulate cv. Ponkan) trees were assessed by the chlorophyll a fluorescence (OJIP) transient. Magnesium deficiency decreased leaf CO₂ assimilation and carbohydrates, but had no effect on intercellular CO₂ concentration. Activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) and concentrations of Chlorophyll (Chl) and carotenoids (Car) decreased to a lesser extent than CO₂ assimilation. Chlorophyll a fluorescence transient from Mg‐deficient leaves had increased O step and decreased P step, accompanied by positive ΔL, ΔK, ΔJ, and ΔI bands. Magnesium deficiency decreased maximum quantum yield of primary photochemistry (F_v/F_m), quantum yield of electron transport from Q<$>_A^‐<$> to the photosystem I (PSI) end electron acceptors (φ_R0), maximum amplitude of IP phase and total performance index (PI_{tot, abs}), but increased deactiviation of oxygen‐evolving complex (OEC) and energy dissipation. Magnesium‐deficient leaves had higher or similar activities of antioxidant enzymes except for lower catalase (CAT) activity, higher or similar concentrations of antioxidant metabolites, and a higher ratio of Car : Chl. Magnesium‐deficiency did not affect concentration of malondialdehyde (MDA) and ratios of ascorbate (ASC) to ASC + dehydroascorbate (DHA) and reduced glutathione (GSH) to GSH + oxidized glutathione (GSSG). In conclusion, Mg deficiency–induced impairment of the whole photosynthetic electron transport chain may be the main factor contributing to decreased CO₂ assimilation. Enhanced energy dissipation and antioxidant metabolism provide sufficient protection to Mg‐deficient leaves against photo‐oxidative damage.     

胡麻异质型ACCase亚基基因的克隆与表达分析

为研究胡麻异质型乙酰辅酶A羧化酶BCCP、BC、α-CT和β-CT四个亚基基因的生物学功能,采用基因克隆、生物信息学和RT-PCR技术分别对胡麻accA、accB、accC和accD 4个基因进行分析。结果发现陇亚10号accA基因编码α-CT亚基,CDS序列全长为2364 bp,编码787个氨基酸;accB基因编码BCCP亚基,CDS序列全长为1173 bp,编码275个氨基酸;accC基因编码BC亚基,CDS序列全长为1574 bp,编码527个氨基酸;accD基因编码β-CT亚基,CDS序列全长为1137 bp,编码378个氨基酸,且4个基因编码的蛋白都是脂肪酸系数较高的亲水性蛋白。RT-PCR结果表明,胡麻accA、accB、accC和accD 4个基因在3个胡麻品种(高含油量的张亚2号、中含油量的陇亚10号和低含油量的R2-17)的不同时期不同组织的表达模式不同,accA、accB、accC和accD四个基因在R2-17、陇亚10号和张亚2号3个胡麻品种所有时期的不同组织中均有表达,但在种子中的表达量均明显高于其他组织,尤其在种子发育10~25 d油脂快速积累时期,4个基因的表达量都迅速增加并达到最高峰。研究表明异质型乙酰辅酶A羧化酶基因可能调控胡麻种子发育前期油脂的合成积累。     

木兰门作物RubisCO大亚基的分子适应性进化研究

分子进化中发生正选择的一个标志是密码子的错义替换（dN,氨基酸替代）比同义替换（dS,氨基酸不变）有更高的替换速率,计算dN与dS之比ω能衡量蛋白质的进化趋势和所受到进化压力的大小。ω=1、〈1和〉1分别说明蛋白质在进化过程中受到中性选择、负选择和正选择。     

高光效大豆光合特性的研究─Ⅵ高光效大豆C_4—途径的探讨

本文研究了不同大豆品种（系）的与Ｃ_４—途径有关的ＰＥＰ羧化酶，ＮＡＤ（Ｐ）—苹果酸酶和丙酮酸磷酸双激酶。结果表明，上述三种酶活性在大豆品种（系）间具有明显的差异，尤以高光效品种（系）的Ｃ_４—途径关键性酶类的活性明显地高于低光效的品种，说明在Ｃ_３—植物中存在着活跃的ＣＯ_２β—羧化作用，从而有利于提高光合效率。     

Evaluation of the Heterosis on Leaf Photosynthesis of Remote-Cross F1 Rice (Oryza saliva L.)

The heterosis of leaf photosynthesis was studied on the main characters included in the range from CO₂exchange rate (CER) to enzymatic activity using a remote cross F, rice. The CER was significantly higher than those of the parental strains, showing a 111 % heterosis effect on average; at the same time strong heterosis was observed for the leaf area production and growth. Also stomatal and mesophyll conductances increased in the F₁ rice, which may contribute to the increase in CER. Chlorophyll content (Ch1), soluble protein content (SPC) and ribulose 1,5-bisphosphate (RuBP) carboxylase activity (RCA) were measured as the internal factors related to photosynthesis, and compared between the F₁, rice and the parents. For all these factors, the F₁ rice showed low values compared to the parents. Positive heterosis was not expressed here. On the other hand, the specific activity of RCA (RCA/SPC) increased in the F₁, rice, showing a 120% heterosis effect. This may be regarded as one of the main causes for the increase in CER of the F₁, rice. High CER expressed as heterosis concurrently with large leaf area production is one of the important findings in our study, and this may suggest a high possibility of further improvement in biomass production or yield of rice by gathering the advantageous elements into a hybrid plant.     

盐胁迫对黄瓜幼苗光合作用及其关键酶基因表达特性的影响

以对盐胁迫敏感性不同的两个黄瓜品种中农大22号和戴多星为材料,研究了盐胁迫下黄瓜幼苗叶片光合特性、叶绿体超微结构以及光合作用关键酶1,5-二磷酸核酮糖羧化酶/加氧酶(Rubisco)和磷酸烯醇式丙酮酸羧化酶(PEPC)活性及其编码基因表达的变化。结果表明:盐胁迫(150 mmol·L~(-1)NaCl处理)下,黄瓜幼苗光合色素(叶绿素和类胡萝卜素)含量、净光合速率、暗呼吸速率和蒸腾速率显著降低;叶绿体类囊体片层结构垛叠程度下降,淀粉粒变小且数量减少;Rubisco大亚基编码基因rbc L、PEPC编码基因Csppc2的表达水平先响应性上调,随后下降;Rubisco和PEPC活性呈降低趋势。相对中农大22号,戴多星具有较强的盐胁迫耐受性。     

Root restriction-induced limitation to photosynthesis in tomato (Lycopersicon esculentum Mill.) leaves

Root restriction often depresses photosynthetic capacity and the mechanism for this reduction, however, remains unclear. To identify the mechanism by which root restriction affects the photosynthetic characteristics, tomato (Lycopersicon esculentum Mill.) seedlings were subjected to root restriction stress with or without supplemental aeration to the nutrient solution. With the development of the root restriction stress, CO₂ assimilation rate was decreased only in confined plants without supplemental aeration. There were also significant decreases in leaf water potential, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and increases in the stomatal limitation (l) and the xylem sap ABA concentration. Meanwhile, the maximum carboxylation rate of Rubisco (V_cmax) and the capacity for ribulose-1,5-bisphosphate regeneration (J_max) also decreased, followed by substantial reductions in the quantum yield of PSII electron transport (Φ_PSII). Additionally, root restriction resulted in accumulation of carbohydrates in various plant tissues irrespective of aeration conditions. It is likely that root restriction-induced depression of photosynthesis was mimicked by water stress.     

引种到青藏高原大田的玉米叶片中磷酸烯醇式丙酮酸羧化酶活性的日变化

引种到青藏高原大田的玉米,其拔节期的全天光合进程中,叶片中磷酸烯醇式丙酮酸羧化酶(PEPC)活性总是大于相应时间点的净光合速率(Pn),且全天变化幅度较Pn缓和.通过研究PEPC活性和Pn之间差异的全天变化,分析了环境因子(如光强、气温)和气孔状态对光合作用的影响.     

Hypoglycemic effect of protopanaxadiol-type ginsenosides and compound K on Type 2 diabetes mice induced by high-fat diet combining with streptozotocin via suppression of hepatic gluconeogenesis

Compound K (CK) is a final intestinal metabolite of protopanaxadiol-type ginsenosides (PDG) from Panax ginseng. Although anti-diabetic activity of CK have been reported with genetic mouse models (db/db mice) in recent years, the therapeutic usefulness of CK and PDG in type 2 diabetes, a more prevalent form of diabetes, remains unclear. In the present investigation, we developed a mouse of non-insulin-dependent diabetes mellitus that closely simulated the metabolic abnormalities of the human disease. For this purpose, type 2 diabetes was induced in male ICR mice by combining of streptozotocin. The male ICR mice fed with HFD for 4 weeks received 100 mg/kg of STZ injected intraperitoneally. After 4 weeks, mice with fasting (12 h) blood glucose levels (FBG) above 7.8 mmol/L were divided into 3 groups (n = 12) and treated with vehicle (diabetes model, DM), 300 mg/kg/day of PDG and 30 mg/kg/day of CK for 4 weeks while continuing on the high-fat diet. Hypoglycemic effects of CK and PDG were consistently demonstrated by FBG levels, and insulin-sensitizing effects were seen during oral glucose tolerance testing (OGTT). Moreover, the mechanism of hypoglycemic effect in type 2 diabetic mice was examined. Gluconeogenic genes, Phosphoenolpyruvate carboxykinase (PEPCK) and Glucose-6-phosphatase (G6Pase), were decreased in two treatment groups with CK showing greater effects. These findings demonstrated the hypoglycemic and insulin-sensitizing capabilities of CK on type 2 diabetes induced by HFD/STZ via down-regulation of PEPCK and G6Pase expression in liver.     

Nutritional regulation of gene expression and enzyme activity of phosphoenolpyruvate carboxykinase in the hepatic gluconeogenesis pathway in golden pompano (Trachinotus ovatus)

Phosphoenolpyruvate carboxykinase (PEPCK) is known to exist as mitochondrial (PEPCK‐M) and cytosolic isoforms (PEPCK‐C). They are involved in glucose production and play vital roles in regulating glucose homeostasis. This study aimed to (1) clone and characterize PEPCK‐C cDNA from golden pompano fish (Trachinotus ovatus), which are known to have poor utilization of dietary carbohydrates, and (2) analyze the regulation of its expression by varying dietary carbohydrate‐to‐lipid ratios and nutritional status. A full length golden pompano PEPCK‐C cDNA fragment of 2,652 bp was cloned, which contains an open reading frame of 1,875 bp encoding 624 amino acids and shows a high homology to cobia (Rachycentron canadum) PEPCK‐C sequence (92% similarity). The analysis of tissue distributions of PEPCK‐C mRNA showed that a high abundance of PEPCK‐C was expressed in golden pompano liver, followed by kidney; while lower expression levels were found in the heart and intestine. In liver, PEPCK is under the regulation of dietary composition and nutritional status at the enzymatic and molecular levels. Our results indicate that PEPCK‐C plays a modulating role in the adaptation of hepatic gluconeogenesis to different nutrient conditions. Thus, the absence of molecular inhibition of gluconeogenic PEPCK gene expression in rainbow trout (Oncorhynchus mykiss) and gilthead sea bream (Sparus aurata), which can at least partially account for their poor utilization of dietary carbohydrate, is specific to these species and is not observed in golden pompano. Further studies that examine, at the enzymatic and molecular levels, other key enzymes involved in hepatic glucose metabolism are necessary to understand the poor utilization of carbohydrates in golden pompano.