Morphological and crystalline characterization of NaOH and NaOCl treated Agave americana L. fiber

This study investigates the effect of NaOH and NaOCl treatments on chemical composition, morphology and crystalline structure of Agave americana L. fibers. These fibers have been subjected to NaOCl and NaOH alkali treatments at different concentrations.The percentages of lignin and hemicellulose show a decrease with alkaline treatments which, in turn, induces a modification of both morphological and crystalline structures.Unit cell dimensions and crystallite size were more affected with NaOH treatment than NaOCl one. This may result from the mercerisation process which occurs with caustic soda treatment.The observed defibrillization on the treated fiber surface proves the dissolution of the non-cellulosic components present in the fiber cell wall by NaOH and NaOCl treatments. These morphological changes may improve the interaction between matrix and fiber in composites.     

Genetic diversity, population structure and relationships of Tunisian Thymus algeriensis Boiss. et Reut. and Thymus capitatus Hoffm. et Link. assessed by isozymes

The genetic diversity and population structure of two Tunisian Thymus species (Thymus algeriensis and Thymus capitatus), from 46 natural populations growing in six bioclimates, were analysed by starch gel electrophoresis using eight isozymes. The genetic diversity within populations varied at species level. Variation in T. algeriensis was higher than that observed for T. capitatus, and exclusive alleles were detected for the two studied species. A high differentiation among populations, for each species, estimated by Wright's F-statistics was revealed. In each species, a high level of inbreeding within populations induced by Wahlund effect was observed. A relatively high level of differentiation associated with a restricted gene flow among species was revealed. The PCA and UPGMA analysis, performed on all populations, showed two distinct groups with respect of specific differentiation level. The high genetic divergence between the two species corroborates their taxonomic status, as previously reported using morphological traits. The strategy for the management and conservation of populations should be made for each taxa according to its level of diversity and bioclimate.     

蝴蝶兰叶绿体基因组密码子使用的相关分析

通过对蝴蝶兰叶绿体基因组全序列密码子的研究,利用Codonw软件进行统计分析,得出密码子第三位置GC含量为31.41%,明显低于第一位置和第二位置的GC含量,说明密码子第三位置富含AT。从对应分析中得出其叶绿体密码子偏好性与其基因表达水平密切相关,且受到突变和选择压力的共同影响。将高表达优越密码子分析法和高频密码子分析法相结合,确定了20个蝴蝶兰叶绿体的最优密码子。上述结果对今后兰花的分子系统进化和高表达转基因研究具有重要意义。     

高校开展国际科技合作与交流的现状与对策——以中国农业大学为例

在全球科技一体化的大环境下,高校成为双边、多边、官方、民间等多种国际科技合作的主体,虽然在多层次、多渠道、全方位国际科技合作格局中发挥了重要的作用,并为国家的科技发展作出了积极贡献,但还存在经费投入不足、合作质量不高、自主性差、重视不够、管理不力等不容忽视的问题。文章针对这些问题,提出了应加大国际科技合作的投入强度;整合优势学科,突出重点,提高合作层次;提高重视程度,加强管理,切实提高中国在国际科技合作中的地位等对策建议。     

1RS·1BL易位在川农号系列小麦新品种选育中的作用

世界上广泛使用的1RS·1BL易位系遗传基础单一,已不能满足世界小麦育种的需要。本课题组培育了不同遗传基础的1RS·1BL易位系,并按照高产优质抗病的选育方向,用于“川农”系列小麦新品种的选育。为了深入了解1RS·1BL易位染色体的传递规律和育种价值,使用酸性聚丙烯酰胺凝胶电泳（APAGE）、Giemsa C带技术、DNA原位杂交技术对13个川农号小麦新品种及4个进入区域试验的新品系进行了检测,并对这17份供试材料的抗病性、农艺性状和主要品质进行了鉴定。结果证明川农10号、川农11、川农20含有来源于Aurora 的1RS·1BL易位染色体,川农12、川农17、川农18和R291是含新合成的1RS·1BL易位染色体的新品种（系）。分析结果表明,目前利用外源种质的小麦育种中,决定1RS·1BL易位能否存在于新品种中的第一选择压仍是抗病性,农艺和品质性状则是第二、三位的选择因素。本研究指出,持续利用1RS·1BL易位染色体培育高产优质抗病的小麦新品种的关键问题是发掘黑麦1RS本身的基因资源,在优先创建1RS·1BL易位系抗病性的遗传多样性的同时,创建农艺与品质性状的遗传多样性。     

ABA在植物细胞抗氧化防护过程中的作用

水分胁迫是一种影响植物生长发育、限制作物产量的重要环境因子,植物激素脱落酸（ABA）在调节植物对水分胁迫响应的过程中起重要作用。ABA不仅可以通过诱导气孔关闭来调节植物水分代谢,而且可以通过诱导脱水耐性蛋白的表达来增强植株对水分胁迫的抗性。越来越多的证据表明,ABA增强水分胁迫耐性的作用与其诱导的抗氧化防护系统有关。本文综述了ABA诱导活性氧产生、抗氧化防护酶基因表达、抗氧化防护酶活性增强方面的新进展,进一步分析了NADPH氧化酶、激酶磷酸化反应、Ca^2＋与活性氧之间的“交谈”在ABA诱导的抗氧化防护反应中的作用,认为：ABA诱导的抗氧化作用在植物细胞内的信号转导途径是网络,而不是直线通路,蛋白激酶磷酸化反应是H2O2传递信号的主要方式。     

Limited evidence for genetic variation for resistance to the white spot syndrome virus in Indian populations of Penaeus monodon

There has been a highly detrimental impact of the white spot syndrome virus (WSSV) on black tiger shrimp (Penaeus monodon) aquaculture in India. Currently, no cost‐effective measures are available for controlling the disease. One alternative is to improve WSSV resistance through a selective breeding programme for disease‐resistant shrimp, provided that genetic variation exists for this trait. The aim of this study was to evaluate the evidence for genetic variation in resistance to WSSV in P. monodon sourced from Indian populations. Post‐larval shrimp (n=1950) from 54 full‐sibling families were challenged with WSSV using WSSV‐infected mince meat. The heritability was estimated using four different statistical models fitted to the resulting time to death data, including two linear models and two Weibull proportional hazard frailty models. None of the estimated heritabilities were significantly different from zero. We suggest three possible explanations for these results: there actually is very little variation between P. monodon in WSSV resistance and all individuals are highly susceptible to the disease; there is genetic variation in resistance to WSSV in P. monodon but we did not find it in our experiment because the level of challenge in the experiment was too high to allow genetic differences to be expressed; the variation is due to mutations conferring resistance, which are at a low frequency in the population, and we did not sample a broad enough genetic base to capture these mutations.     

Foraging behaviour,digestion and growth performance of sheep grazing on dried vetch pasture cropped under conservation agriculture

This study aimed to investigate the replacement value of half time grazing of wheat stubbles by vetch, which had been cropped under the context of conservation agriculture (CA). Three grazing treatments were evaluated on Barbarine lambs (initial BW 18 ± 1.42 kg). Treatment 1 consists of 6-hr grazing on dried vetch only (V). For treatment 2, the sheep were grazing 3 hr on wheat stubbles in morning and 3 hr on dried vetch in the afternoon (VWS). Treatment 3 consists of 6-hr grazing of wheat stubbles only (WS). At grain maturity stage, biomass yield of vetch averaged 7 tons DM/ha allowing a grazing period of 2 consecutive months. Along this period, vetch conserved its pods indehiscent. Biomass and nutritive value of vetch and wheat stubbles were decreasing from the start to the end of the grazing period. Residual biomass was higher in vetch and wheat stubble assigned to treatment VWS. WS lambs spent more time on walking and standing, while V and VWS lambs allocated more time on biomass uptake. The DM, OM and CP intakes were higher in animal grazing vetch alone or combined to wheat stubble. Rumen fermentation parameters (pH, ammonia nitrogen concentration and protozoa count) were not affected (p > .05) by any of the three treatments. The average daily gain of lambs on V and VWS lambs was three times greater (p < .05) than that of WS lambs (164, 152 and 49.5 g respectively). Cold carcass yield averaged 444, 428 and 388 g/ kg for lambs assigned to V, VWS and WS treatments respectively. It is concluded that grazing vetch alone or combined with WS increased substantially the growth performance and carcass yield of lambs compared with WS grazing only. Therefore, dried vetch grazing could be a solution to make possible mulching and biomass uptake by sheep under the context of CA.     

长江下游棉花落叶型黄萎病发生消长与气象因子关系分析

１９９３～１９９７ 年, 在江苏省常熟市徐市镇棉花落叶型黄萎病地（致病小种为落叶型ＪＣ５）,对苏棉８ 号从６ 月初至９ 月中旬进行棉花黄萎病调查, 并结合当地的气温、雨日等气象因子对黄萎病的发生消长关系进行统计分析。结果表明, 平均气温２３℃最适宜发病, 平均气温大于２８℃时发病停止（隐症）。黄萎病的日增病指与平均气温、雨日相关性较强, 与雨量相关性较差。合并５ 年的资料, 通过多因子筛选, 得出日增病指（Ｙ）与雨日（Ｘ２）、大于２３℃的有效积温值（Ｘ１）的关系式： Ｙ＝ － ０．１４９４９Ｘ１＋ ０．１４５４４Ｘ２＋ ０．９３５５１。     

外源C4二羧酸对转玉米PEPC基因水稻C4光合途径的促进作用

以转PEPC基因水稻和野生型水稻Kitaake为材料, 研究了不同基因型水稻叶片中的C4光合微循环及其功能。通过测定与光合C4途径有关的关键酶,如磷酸烯醇式丙酮酸羧化酶(PEPC)、NADP苹果酸酶(NADP-ME)、NADP苹果酸脱氢酶(NADP-MDH)和丙酮酸磷酸双激酶(PPDK),说明野生型水稻叶片中具有完整的C4光合酶体系;用外源草酰乙酸(OAA)或苹果酸(MA)饲喂叶切片或叶绿体后明显增加光合速率,证明野生型水稻中具有一个有限的光合C4微循环。将玉米的PEPC基因导入原种水稻后,可大幅度提高光合C4微循环的速率。测定不同基因型的CO2交换速率,看出水稻中C4光合微循环的增强有提高净光合速率(Pn)和降低Pr/Pn比值的作用。叶绿素荧光特性分析表明,C4光合微循环的增强伴随着PSⅡ电子传递效率(Fv/Fm)和光化学猝灭(qp)的增加,以及非光化学猝灭(qN)的降低。 