Antibacterial activity of embelin

Embelin, a benzoquinone-derivative isolated from Embelia ribes, when tested for its antibacterial potential exhibited significant inhibition against five and moderate activity against three strains of the 12 bacteria tested.     

Insecticidal action of the polyphenolic rich fractions from the stem bark of Streblus asper on Dysdercus cingulatus

Extracts from the stem bark of Streblus asper possess insecticidal activity against the fifth instar of Dysdercus cingulatus. Methanolic extract showed an LC(50) value of 5.56 microg/insect. Partition with chloroform increased the insecticidal activity (LC(50) 2.01 microg/insect). Three polyphenolic rich fractions were obtained from silica-gel column chromatography of the chloroform fraction and found to have noteworthy insecticidal activity (LC(50): 1.82 microg, 2.70 microg, 2.26 microg/insect) by topical application. This may provide a useful beginning for the development of biopesticides.     

Carbon stock and rate of carbon sequestration in Dipterocarpus forests of Manipur,Northeast India

We examined the carbon stock and rate of carbon sequestration in a tropical deciduous forest dominated by Dipterocarpus tuberculatus in Manipur,North East India.Estimation of aboveground biomass was determined by harvest method and multiplied with density of tree species.The aboveground biomass was between18.27–21.922 t ha-1and the carbon stock ranged from9.13 to 10.96 t C ha-1across forest stands.Aboveground biomass and carbon stock increased with the increase in tree girth.The rate of carbon sequestration varied from1.4722 to 4.64136 t ha-1year-1among the dominant tree species in forest stands in tropical deciduous forest area.The rate of carbon sequestration depends on species composition,the density of large trees in different girth classes,and anthropogenic disturbances in the present forest ecosystem.Further work is required to identify tree species having the highest potential to sequester CO2 from the atmosphere,which could lead to recommendations for tree plantations in a degraded ecosystem.     

水稻始穗期和齐穗期施氮钾肥的生理性状及增产效果

水稻始穗斯和齐穗期施氮肥或氮钾肥，能提高结实期间叶片含氮量，叶绿素含量、ＲｕＢＰ羧化酶活性，光合速率和根系活力，增加剑叶中＾１４Ｃ－光合同化物的输出率及其分布在稻穗中的比例，促使中部和下部枝梗的谷粒灌浆充实，提高结实率，千粒重和稻谷产量。始穗期和齐穗期施氮钾肥比单施氮肥的效果好。     

Insecticidal, antifeedant and oviposition deterrent effects of the essential oil and individual compounds from leaves of Chloroxylon swietenia DC

Essential oil from the leaves of Chloroxylon swietenia DC. was obtained by hydrodistillation and cold extraction, and the chemical composition was determined by gas chromatography and gas chromatography-mass spectrometry. The major identified components were limonene, geijerene, pregeijerene, germacrene D and trans-beta-ocimene. Laboratory bioassays of the essential oil and four constituents of essential oil isolates were evaluated for insecticidal, antifeedant and oviposition deterrent effects on tobacco cutworm, Spodoptera litura (F.). Toxicity was determined by topical application of the isolates at varying concentrations. Pure oil, geijerene and pregeijerene were found to be more toxic, with LD50 values of 28.6, 35.4 and 40.7 microg per larva respectively. Maximum feeding deterrence was noted for geijerene and pregeijerene, with DC(50) values of 82.5 and 95.1 microg cm(-2) respectively. Furthermore, pure oil, geijerene and pregeijerene displayed oviposition deterrence, even at low concentrations. These results indicate that these natural products may lead to useful, biodegradable, environmentally safe insect control agents.     

Serological Methods for Detection of Polymyxa graminis, an Obligate Root Parasite and Vector of Plant Viruses

A purification procedure was developed to separate Polymyxa graminisresting spores from sorghum root materials. The spores were used as im-munogen to produce a polyclonal antiserum. In a direct antigen coating enzyme-linked immunosorbent assay (DAC ELISA), the antiserum could detect one sporosorus per well of the ELISA plate. In spiked root samples, the procedure detected one sporosorus per mg of dried sorghum roots. The majority of isolates of P. graminis from Europe, North America, and India reacted strongly with the antiserum. Interestingly, P. graminis isolates from the state of Rajasthan (northern India), from Pakistan, and an isolate from Senegal (West Africa) reacted weakly with the antiserum. The cross-reactivity of the serum with P. betae isolates from Belgium and Turkey was about 40% of that observed for the homologous isolate. There was no reaction with common fungi infecting roots or with the obligate parasite Olpidium brassicae. However, two isolates of Spongospora sub-terranea gave an absorbance similar to that observed with the homologous antigen. The DAC ELISA procedure was successfully used to detect various stages in the life cycle of P. graminis and to detect infection that occurred under natural and controlled environments. A simple procedure to conjugate antibodies to fluorescein 5-isothiocyanate (FITC) is described. Resting spores could be detected in root sections by using FITC-labeled antibodies. The potential for application of the two serological techniques for studying the epidemiology of peanut clump disease and for the characterization of Polymyxa isolates from various geographical origins is discussed.     

两系杂交稻始穗期追施氮钾肥提高叶片光合功能的作用

研究表明，将占总肥量１／３左右的氮或氮钾肥在始穗期施用，能明显提高两系杂交水稻Ｎ３１Ｓ／Ｐ４０剑叶的光合速率、ＲｕＢＰ羧化酶活性、光合磷酸化和Ｈｉｌ反应活性。对乳熟期剑叶叶绿素荧光测定表明，始穗肥处理的ＦＶ和ＦＶ／Ｆｏ比值均明显高于对照。施始穗肥的剑叶中活性氧清除酶活性明显高于对照，丙二醛含量明显低于对照。     

不同光强生态型水稻对始穗期氮钾营养的效应

杂交水稻Ｌｅ／Ｑｉ在施基肥基础上始穗期追施Ｎ,ＮＫ营养比其亲本和仅施基肥（ＮＰＫ）表现剑叶叶绿素（ａ＋ｂ）总量及可溶性蛋白含量多,ＳＰＳ酶活性及ＳＰＳ／Ｆ－１,６－Ｐａｓｅ的酶活性比率高,１４Ｃ－蔗糖同化物从顶３叶及叶鞘的输出率亦高,剑叶含矿质营养Ｋ,Ｃａ,Ｍｎ,Ｍｇ及Ｆｅ也较高。Ｌｅ／Ｑｉ从抽穗期至蜡熟期残留在叶鞘及茎中的可溶性糖及淀粉的量较少,蜡熟期被分配到穗部的量较多,且与谷产量分别呈极显著及显著正相关,谷产量比Ｌｅｍｏｎｔ（母本）高约３２％,比七挂早（父本）高８％,而光合速率则处于亲本之间,偏于母本。     

无机磷对植物叶片光合作用的影响及其机理的研究进展

本文综述了无机磷（Pi）在叶片细胞中的分布、Pi对光合作用的影响及其机理的研究概况。缺磷植株叶片光合速率的下降，主要是阻碍了1，5-二磷酸核酮糖（RuBP）的再生。在源库反馈调节中，Pi起重要作用。