Alanine racemase activity in the microalga <Emphasis Type="Italic">thalassiosira</Emphasis> sp.

ABSTRACT:   In this paper, the authors report the detection of alanine racemase activity in the marine diatom Thalassiosira sp. Since the Thalassiosira sp. was cultured under germ-free conditions, it appeared that D-alanine was not derived from bacteria but was produced through catalysis by algal alanine racemase. The rate of conversion of L-alanine to D-alanine was approximately the same as that for the reverse reaction, and the enzyme catalyzed the equilibration of the D- and L-forms. The crude enzyme preparation obtained from the cells at the stationary phase of the growth cycle had an optimal pH of approximately 9.5. The Lineweaver–Burk analysis showed that the K _m for D- and L-alanine was 16.5 mM and 29.4 mM, respectively. It appears that the enzyme is highly specific for D- or L-alanine because it does not catalyze the racemization of other amino acids. In addition, after gel filtration, the enzyme did not require exogenous pyridoxal 5'-phosphate (PLP) for its activity, however, the effects of several chemicals suggest that the enzyme may be PLP-dependent. The enzyme is more similar to that found in invertebrates when compared with that found in bacteria. This is the first report on the occurrence of alanine racemase activity in the microalga Thalassiosira sp.     

Variability in timing and magnitude of spring bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan

The spring bloom of phytoplankton is a well-established, regular, seasonal event in the western subarctic Pacific and is considered one of the most important conditions of massive production of pelagic fishes. A series of 12 cruises was conducted from 1990 to 1992 to examine the timing and magnitude of the spring phytoplankton bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan. An interannual variability in the bloom events was also analysed. On the basis of hydrographical characteristics, the study area was divided into three water masses: the Oyashio Water Mass, the Mixed Water Mass, and the Coastal Water Mass. Spring blooms were observed first in April in the Oyashio and the Coastal Water Masses, and continued to May in 1991 and 1992. However, no bloom was recorded in the Mixed Water Mass. High nutrient supply into the surface mixed layer during winter is likely to be one of the factors supporting an intense spring bloom in the Oyashio Water Mass. A significant positive relationship between log-transformed surface chlorophyll a concentration and maximum density gradient (MDG) within the euphotic layer was obtained in April, indicating the importance of vertical stability of the water column in the initiation of spring blooms in the Oyashio and the Coastal Water Masses. The spring blooms in 1991 were much more extensive and lasted longer than in 1990. It is suggested that meteorological conditions and abundance of grazers were responsible for this interannual difference.     

甘肃平凉市苹果花期冻害风险分析及区划

利用平凉7县（区）气象资料、6个县（区）的苹果物候观测资料和产量资料,对苹果花期冻害指标、因冻减产情况及不同等级冻害发生频率进行了分析。根据平凉近年来苹果花期冻害实地调查,将花期冻害分为三种强度等级即重度（T≤-3.5℃）、中度（T≤-1.5℃）和轻度（T≤0℃）,不同冻害等级对应不同的减产率。 在平凉7个县（区）中,华亭花期冻害发生最严重,不同等级的冻害发生1年1～2次,崇信花期冻害则最轻,不同等级冻害3年1次,其他县（区）1～2年1次,全市不同等级冻害的频率分布表现出轻度＞中度＞重度的特点。在此基础上,以冻害灾损率作为风险区划指标,将苹果花期冻害风险分为3个区：高风险区、中风险区和低风险区。本市多数区域属于中风险区和低风险区,重度冻害发生较少,但中度冻害和轻度冻害发生仍较频繁。建议全市在目前果园布局的基础上,应进一步加大中东部低风险区的苹果种植。     

胶州湾浮动弯角藻赤潮生消动态过程及其成因分析

分析了1999年6月8日-15日胶州湾东北养殖消耗域浮动弯角藻赤潮生消动态过程中各环境因子的变化及赤潮成因，结果表明，该海域无机营养盐含量较高，为赤潮的发生提供了必需的营养物质；赤潮发生前天气闷热无雨，有利于浮动弯角藻的快速生长繁殖；赤潮形成至发展期该海域盛行南风，浮动弯角藻的物理性聚集对赤潮迅速形成有重要影响；赤潮维持阶段天气稳定，赤潮持续时间较长；最终无机磷、活性硅酸盐的耗尽使赤潮逐步走向消亡。     

鲍育苗用底栖硅藻的研究进展

鲍是珍贵的海产贝类之一，具有很高的营养价值。但近几年，我国台湾、福建、广东以及海南等省发生大规模九孔鲍苗掉板死亡的现象，很多鲍鱼场连续多月多批培苗，但或颗粒无收或每批次收获率极低，不到正常的10％。鲍苗掉板已是南方养鲍业中的一个非常普遍的问题，给我国南方各省鲍鱼养殖业带来极大的负面影响。     

刺参大水体人工育苗研究

剌参大水体育苗,采用降低初耳幼体放养密度,适当减少单胞藻投喂量、加大换水量、通气、增设机动进水系统等措施,培育出稚参1911.5万头,幼参258.36万头,单位水体平均出苗量稚参为3.823万头/m~3,幼参为5167头/m~3。以食用鲜酵母为饵的耳状幼体能正常发育变态,稚参出苗量平均达1.6万头/m~3。稚参的附着、成活,成长与附着基的规格有关。     

尼罗与奥利亚罗非鱼对池塘蓝藻水华及水质影响的研究

利用尼罗罗非鱼和奥利亚罗非鱼进行了池塘抑藻试验，采用血球计数板测定水体中的微囊藻密度，并对水体理化性质进行了检测分析。试验结果表明，罗非鱼能有效消减水体中蓝藻生物量，降低水体藻毒素浓度，并对水体TN、TP产生一定影响。其中奥利亚罗非鱼试验组蓝藻初始密度为1．53-108cells／L，下降至0．86-108eells／L，降低43．79％；尼罗罗非鱼组蓝藻初始密度为1．54-108cells／L，下降至O．51×108cells，L，降低66．88％。水体总磷含量无显著变化，总氮含量有所下降，水体微囊藻毒素MC—LR含量随着蓝藻密度的下降而降低，并讨论了尼罗与奥利亚罗非鱼摄食抑制蓝藻的摄食抑制及其对水质的影响。     

微囊藻水华叠加对太湖沉积物中细菌垂直分布的影响

为研究微囊藻水华爆发对沉积物中细菌的影响,加强对富营养化湖泊细菌生态分布和环境调控原理的认识,选取太湖竺山湾沉积物柱状样,经添加高浓度微囊藻培养后,采用聚合酶链式反应-变性梯度凝胶电泳（polymerase chain reaction-denaturing gradient gel electrophoresis;PCR-DGGE）方法,分析细菌在沉积物中的垂直分布特征。结果显示,微囊藻水华叠加对于沉积物剖面表层细菌群落结构影响很小,对沉积物中细菌垂直分布的影响不大,仅在7～9cm深度之间有一定影响。     

Use of Plant Growth Regulators in Blueberry Production in the Southeastern U.S.

Abstract

Blueberry (Vaccinium sp.) production has expanded rapidly in the Southeastern U.S. over the past two decades, and various production problems have been encountered. These problems include poor pollination, low fruit set, freeze damage, variable yields, and small fruit size among others. Plant growth regulators (PGRs) have been utilized to overcome some production problems with some degree of success. This paper reviews findings of research that has been conducted over the past few years with PGRs and blueberries in the Southeast.     

三角帆蚌对蓝藻的滤食作用及其对沉水植物生长的影响

双壳贝类是淡水生态系统常见的滤食性动物,以浮游植物和有机物悬浮颗粒为食,其作用可能降低蓝藻浓度,从而促进沉水植物生长。通过构建4组(草+蓝藻、草+蓝藻+低生物量蚌、草+蓝藻+高生物量蚌、草)室外微型生态系统,研究了湖泊下风区常见蓝藻堆积浓度下,三角帆蚌(Hyriopsis cumingii)的滤食作用对蓝藻水华和沉水植物苦草(Vallisneria natans)生长的影响。结果表明:(1)蓝藻对苦草的生长具有显著抑制作用,草藻组和草组的相对生长率分别为-7.65mg/g·d和7.19mg/g·d;(2)三角帆蚌对蓝藻具有明显的下行滤食压力,其大小与蚌生物量有关,蚌生物量高时效果明显;(3)三角帆蚌的滤食可以不同程度上缓解蓝藻对苦草的生长抑制,低蚌组和高蚌组苦草相对生长率分别为-5.31mg/g·d和4.24mg/g·d。蓝藻颗粒被滤食后,水体光照条件的改善可能是有蚌组苦草生物量相对较高的主要原因。说明双壳贝类可以通过滤食浮游植物使水体理化环境向着有利于沉水植物生长的方向发展,但这种作用的大小与贝类生物量的合理配置有密切关系。