Carbon accumulation at depth in Ferralsols under zero‐till subtropical agriculture

Conservation agriculture can provide a low‐cost competitive option to mitigate global warming with reduction or elimination of soil tillage and increase soil organic carbon (SOC). Most studies have evaluated the impact of zero till (ZT) only on surface soil layers (down to 30 cm), and few studies have been performed on the potential for C accumulation in deeper layers (0–100 cm) of tropical and subtropical soils. In order to determine whether the change from conventional tillage (CT) to ZT has induced a net gain in SOC, three long‐term experiments (15–26 years) on free‐draining Ferralsols in the subtropical region of South Brazil were sampled and the SOC stocks to 30 and 100 cm calculated on an equivalent soil mass basis. In rotations containing intercropped or cover‐crop legumes, there were significant accumulations of SOC in ZT soils varying from 5 to 8 Mg ha^?1 in comparison with CT management, equivalent to annual soil C accumulation rates of between 0.04 and 0.88 Mg ha^?1. However, the potential for soil C accumulation was considerably increased (varying from 0.48 to 1.53 Mg ha^?1 yr^?1) when considering the soil profile down to 100 cm depth. On average the estimate of soil C accumulation to 100 cm depth was 59% greater than that for soil C accumulated to 30 cm. These findings suggest that increasing sampling depth from 30 cm (as presently recommended by the IPCC) to 100 cm, may increase substantially the estimates of potential CO₂ mitigation induced by the change from CT to ZT on the free‐draining Ferralsols of the tropics and subtropics. It was evident that that legumes which contributed a net input of biologically fixed N played an important role in promoting soil C accumulation in these soils under ZT, perhaps due to a slow‐release of N from decaying surface residues/roots which favored maize root growth.     

大豆油中转基因成分的Nested PCR和Semi-nested PCR检测方法研究

对大豆油中DNA提取方法进行了研究,结果表明CTAB、SDS和Wizard试剂盒提取大豆油DNA均具有良好的效果。利用nested PCR和semi—nested PCR检测大豆（Roundup Ready）油中的转基因成分发现,该方法能够检测到大豆原油中的Lectin基因（112bp）、CaMV35S基因（147bP）和CP4-EPSPS基因（205bp）,检测灵敏度达到10^-6ng／μl;但该方法未能从人豆成品油（一级）中扩增到上述基因,当中的转基因成分DNA含量低于10^-12ng／μl。     

Handling and aflatoxin contamination of white maize in Costa Rica

Projects funded by International Development Research Centre (IDRC) of Canada and the European Commission have enabled the examination of more than 3000 samples of maize collected from all regions of Costa Rica at different stages, from the growing crop through storage to final sale, and at different water contents. Contamination with Aspergillus flavus was frequent and about 80% of samples contained more than 20 ng aflatoxins g-1 grain. Average contamination with aflatoxins in the Brunca Region was > 274 ng g -1 while that in other regions was < 70 ng g -1. Except in Brunca region, where it averaged 376 ng g -1, contamination of grain from commercial sources was slightly less than of that from farms (≤15 ng g-1). It appeared that samples kept on the cob after harvest contained almost no aflatoxin while shelled samples were frequently highly contaminated. Experiments were therefore done in Brunca and Huetar Atlantic Regions, utilising 34 experimental maize crops to study in detail the development of A. flavus and aflatoxin from before harvest, through postharvest treatment before drying and through storage for six months. A. flavus was isolated more frequently from maize shelled immediately after harvest than from that kept on the cob until it could be dried, and from more samples from the Brunca Region than from the Huetar Atlantic Region. Samples harvested with ≥18% water content often contained >70% of grains infected with A. flavus but sometimes there were few grains infected. As found in the initial survey, more aflatoxin contamination developed in shelled maize than in that handled on the cob during the period from harvesting to drying, especially if the delay was more than 5 days, and more in Brunca than in Huetar. Shelled grain contained 400–800 ng aflatoxin g -1 in Brunca but <100 ng g-1 in Huetar while grain kept on the cob contained <30 ng g-1, even with >18% water content. Incidence of Fusarium spp. exceeded 50% except where A. flavus colonized more than 80% of grains. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ca2+-CaM对过氧化氢诱导玉米幼苗耐冷性的影响

H2O2预处理可提高玉米幼苗的耐冷性及其体内钙调素(CaM)活性。阻断胞内Ca2 库的动员(钌红处理)、降低细胞中Ca2 水平(EGTA处理)及抑制CaM活性(TFP和CPZ处理)均可完全消除H2O2诱导的玉米幼苗的耐冷性。阻止胞外Ca2 跨膜进入胞内(La3 处理)并不抑制、甚至还能轻微地提高H2O2诱导的耐冷性。高Ca2 (20mmol.L^-1)处理削弱H2O2诱导的耐冷性。这些结果表明,CaM及胞内Ca2 库在H2O2诱导的玉米幼苗耐冷性的形成过程中起重要作用,而质外体中高浓度Ca2 和跨膜进入胞内会削弱H2O2诱导的耐冷性。     

Removal of selectable marker gene from fibroblast cells in transgenic cloned cattle by transient expression of Cre recombinase and subsequent effects on recloned embryo development

Introduction of selectable marker genes to transgenic animals could create an inconvenience to further research and may exaggerate public concerns regarding biological safety. The objective of the current study was to excise loxP flanked neo^R in transgenic cloned cattle by transient expression of Cre recombinase. Green fluorescent protein gene (GFP) was incorporated to monitor Cre expression; therefore, Cre-expressed cells could be selected indirectly by fluorescence-activated cell sorting (FACS). The neo^R was removed and Cre expressed transiently in GFP-positive colonies; excision of neo^R was confirmed by single-blastocyst PCR in recloned blastocysts, with neo^R-free fibroblast cells as donors. There was no difference (P > 0.05) in rates of cleavage (76.0% vs. 68.8%) or blastocyst formation (56.6% vs. 52.9%) between recloned embryos with neo^R-free or neo^R-included donors. The differential staining of recloned blastocysts were similar (P >0.05) in terms of total cell number (124 vs. 122) and the ratio of ICM (Inner Cell Mass) to the total cell number (38.1% vs. 38.2%). Furthermore, pregnancy and calving rates were not different (P > 0.05) from those of the control. In conclusion, we successfully excised neo^R from transgenic cloned cattle; the manipulation did not affect the developmental competence of recloned preimplantation embryos. This approach should benefit bioreactor and transgenic research in livestock.     

Comparative stability of ammonium- and nitrate-induced nitrate reductase activity in maize leaves

Ammonium sulfate (5 mM) had no effect on nitrate reductase activity during a 3 hr dark incubation, but the enzyme was increased 2.5-fold during a subsequent 24 hr incubation of the maize leaves in light. The enzyme activity induced by ammonium ion declined at a slower rate under non-inducing conditions than that induced by nitrate. The decline in ammonium stimulated enzyme activity in the dark was also slower than that with nitrate. Further. cycloheximide accelerated the dark inactivation of the ammonium-enzyme while it had no effect on the nitrate-enzyme. The experiments demonstrate that increase in nitrate reductase activity by ammonium ion is different from the action of nitrate action.     

Large-scale production of a therapeutic protein in transgenic tobacco plants: effect of subcellular targeting on quality of a recombinant dog gastric lipase

A recombinant dog gastric lipase with therapeutic potential for the treatment of exocrine pancreatic insufficiency was expressed in transgenic tobacco plants. We targeted the protein using two different signal sequences for either vacuolar retention or secretion. In both cases, an active glycosylated recombinant protein was obtained. The recombinant enzymes and the native enzyme displayed similar properties including acid resistance and acidic optimum pH. The proteolytic maturation and the specific activity of the recombinant proteins, however, were found to be dependent on subcellular compartmentalization. Expression levels of recombinant dog gastric lipase were about 5% and 7% of acid extractable plant proteins for vacuolar retention and secretion respectively. This expression system already has allowed the production of tens of grams of purified lipase through open-field culture of transgenic tobacco plants.     

A missense mutant myostatin causes hyperplasia without hypertrophy in the mouse muscle

Myostatin, which is a member of the TGF-beta superfamily, is a negative regulator of skeletal muscle formation. Double-muscled Piedmontese cattle have a C313Y mutation in myostatin and show increased skeletal muscle mass which resulted from an increase of myofiber number (hyperplasia) without that of myofiber size (hypertrophy). To examine whether this mutation in myostatin gene affects muscle development in a dominant negative manner, we generated transgenic mice overexpressing the mutated gene. The transgenic mice exhibited dramatic increases in the skeletal muscle mass resulting from hyperplasia without hypertrophy. In contrast, it has been reported that a myostatin mutated at its cleavage site produces hypertrophy without hyperplasia in the muscle. Thus, these results suggest that (1) the myostatin containing the missense mutation exhibits a dominant negative activity and that (2) there are two types in the dominant negative form of myostatin, causing either hypertrophy or hyperplasia.     

弱光胁迫对不同基因型玉米生长发育和产量的影响

以不同基因型玉米为材料,在玉米生长发育的3个主要阶段(苗期、穗期、粒期)进行分期遮光试验,研究不同时期弱光胁迫对不同基因型玉米生长发育和产量的影响。结果表明,遮光延缓了玉米叶片的出生速度,使叶片变薄;遮光可以延缓叶片的衰老,但遮光解除后则加速叶片的衰老;遮光造成植株高度增加,但恢复正常光照后,其株高却逐渐低于对照;遮光使干物质积累下降,抽雄吐丝日期推迟,尤其是吐丝日期推迟更多,并使产量降低,但不同基因型玉米不同遮光处理下降程度不同。试验的4个品种中,掖单2 2和豫玉2号受遮光影响较小,而掖单36 38和丹玉13受影响较大,即不同基因型玉米对弱光胁迫的敏感性不同