A Feedback Mechanism to Control Apoptosis Occurs in the Digestive Gland of the Oyster Crassostrea gigas Exposed to the Paralytic Shellfish Toxins Producer Alexandrium catenella

To better understand the effect of Paralytic Shellfish Toxins (PSTs) accumulation in the digestive gland of the Pacific oyster, Crassostrea gigas, we experimentally exposed individual oysters for 48 h to a PSTs producer, the dinoflagellate Alexandrium catenella. In comparison to the effect of the non-toxic Alexandrium tamarense, on the eight apoptotic related genes tested, Bax and BI.1 were significantly upregulated in oysters exposed 48 h to A. catenella. Among the five detoxification related genes tested, the expression of cytochrome P450 (CYP1A) was shown to be correlated with toxin concentration in the digestive gland of oysters exposed to the toxic dinoflagellate. Beside this, we observed a significant increase in ROS production, a decrease in caspase-3/7 activity and normal percentage of apoptotic cells in this tissue. Taken together, these results suggest a feedback mechanism, which may occur in the digestive gland where BI.1 could play a key role in preventing the induction of apoptosis by PSTs. Moreover, the expression of CYP1A, Bax and BI.1 were found to be significantly correlated to the occurrence of natural toxic events, suggesting that the expression of these genes together could be used as biomarker to assess the biological responses of oysters to stress caused by PSTs.     

不同镉浓度处理下水稻植株镉含量变化及其镉调控相关基因表达分析

以地上部镉含量不同的籼稻和粳稻品种各6个为材料,采用水培试验,设置6个镉浓度,研究了不同浓度镉处理对不同水稻品种植株生长、镉含量和相关重金属转运蛋白基因表达水平的影响。结果表明,镉胁迫对水稻生长有抑制作用,表现为苗高、地上部干物质量和叶绿素含量下降。在不同镉浓度处理下,植株根部和地上部的镉含量存在显著的基因型差异,植株中镉从根部向地上部的转运可能是水稻品种间以及籼粳亚种间地上部镉含量差异的主要原因,根部镉的吸收量影响较小。在0.50到2.00mg/kg的高镉处理梯度间,部分水稻品种地上部出现镉积累饱和现象(镉含量增加较少,部分水稻品种地上部镉含量甚至显著降低);在此镉浓度处理下,OsNRMAP1、OsIRT2和OsNAS2的表达水平显著上调,这可能与植株对镉的吸收调节作用相关。     

茶树对硒吸收累积特性及其硒调控相关基因的表达分析

本文采用沙培试验,从动态角度研究了不同时间和不同浓度下茶树对硒的吸收累积规律,并分析相关基因的表达特点。结果发现,茶树不同部位对硒的累积量存在较大差异,大部分硒保留在根部,在其体内的迁移率较低,硒的累积量和外源硒浓度、培养时间显著相关;当外源硒浓度在0~0.05 mmol·L^-1时,茶树长势良好,但当浓度高于0.10 mmol·L^-1时,茶树表现出中毒症状。荧光定量PCR分析发现,转录因子CsbHLH62及茉莉酸信号途径中的关键基因丙二烯环化氧化酶基因（CsAOC）和脂氧合酶基因（CsLOX6）受到高浓度硒的诱导表达,相关性分析表明,这3个基因的表达量与根系硒含量呈显著正相关。本研究表明,茶树各部位对硒的累积与外源硒浓度和培养时间显著相关,基因CsbHLH62、CsAOC和CsLOX6可能在该过程中发挥着重要作用。     

First Identification of 12β-Deoxygonyautoxin 5 (12α-Gonyautoxinol 5) in the Cyanobacterium Dolichospermum circinale (TA04) and 12β-Deoxysaxitoxin (12α-Saxitoxinol) in D. circinale (TA04) and the Dinoflagellate Alexandrium pacificum (Group IV) (120518KureAC)

Saxitoxin and its analogues, paralytic shellfish toxins (PSTs), are potent and specific voltage-gated sodium channel blockers. These toxins are produced by some species of freshwater cyanobacteria and marine dinoflagellates. We previously identified several biosynthetic intermediates of PSTs, as well as new analogues, from such organisms and proposed the biosynthetic and metabolic pathways of PSTs. In this study, 12β-deoxygonyautoxin 5 (12α-gonyautoxinol 5 = gonyautoxin 5-12(R)-ol) was identified in the freshwater cyanobacterium, Dolichospermum circinale (TA04), and 12β-deoxysaxitoxin (12α-saxitoxinol = saxitoxin-12(R)-ol) was identified in the same cyanobacterium and in the marine dinoflagellate Alexandrium pacificum (Group IV) (120518KureAC) for the first time from natural sources. The authentic standards of these compounds and 12α-deoxygonyautoxin 5 (12β-gonyautoxinol 5 = gonyautoxin 5-12(S)-ol) were prepared by chemical derivatization from the major PSTs, C1/C2, produced in D. circinale (TA04). These standards were used to identify the deoxy analogues by comparing the retention times and MS/MS spectra using high-resolution LC-MS/MS. Biosynthetic or metabolic pathways for these analogues have also been proposed based on their structures. The identification of these compounds supports the α-oriented stereoselective oxidation at C12 in the biosynthetic pathway towards PSTs.