Assessment of a model for intron RNA secondary structure relevant to RNA self-splicing--a review

A widespread class of introns is characterized by a particular RNA secondary structure, based upon four conserved nucleotide sequences. Among such "class I" introns are found the majority of introns in fungal mitochondrial genes and the self-splicing intron of the large ribosomal RNA of several species of Tetrahymena. A model of the RNA secondary structure, which must underlie the self-splicing activity, is here evaluated in the light of data on 16 further introns. The main body or "core structure" of the intron always consists of the base-paired regions P3 to P9 with the associated single-stranded loops, with P2 present also in most cases. Two minority sub-classes of core structure occur, one of which is typical of introns in fungal ribosomal RNA. Introns in which the core structure is close to the 5' splice site all have an internal guide sequence (IGS) which can pair with exon sequences adjacent to the 5' and 3' splice sites to align them precisely, as proposed by Davies et al. [Nature 300 (1982) 719-724]. In these cases, the internal guide model allows us to predict correctly the exact location of splice sites. All other introns probably use other mechanisms of alignment. This analysis provides strong support for the RNA splicing model which we have developed.     

Recherches Cytotaxonomiques et Cytogéographiques surMinuartia sect.Sabulina en Turquie (Caryophyllaceae)

25 populations from Turkey and one of Syria belonging to theSabulina section of the genusMinuartia have been karyologically examined. New chromosome numbers have been recorded forM. mesogitana andM. hybrida subsp.turcica, and a new variety was found in theM. hybrida complex. The origin of the taxa with n = 23 and n = 35 is discussed.

     

A new species ofLiparis (Orchidaceae) from India

Liparis indiraii spec. nova from India is close toL. alata A. Rich. andL. atropurpurea Lindl.     

Corresponding patterns of geographic variation among populations ofSilene latifolia (=S. alba =S. pratensis) (Caryophyllaceae)

Morphological and biochemical data were analysed from 30 greenhouse-grown populations of EuropeanSilene latifolia. Six separate character sets (flavones, seed, pollen, capsules, male and female flower morphology) were used in the analyses. There was broad-scale congruence between trends of geographic variation in most character sets, with the populations being assigned to western (or southern and western) and eastern clusters. The eastern and western clusters abut along a transition zone that runs roughly from Belgium to the northern Balkans; this zone represents a region of relatively rapid change and contains populations intermediate between the eastern and western clusters. Variation in flower morphology was weak and discordant with variation in the other character sets. The origin and maintenance of the variation pattern is discussed in terms of migrational history and hybrid zones.     

温度对赤眼蜂的发育和羽化的影响

赤眼蜂的生长发育温度大致为10—35℃,可区分为全期正常发育温度(16—33℃);部分虫期发育温度(10—11℃);全期发育阀限温度(12—15°及34—35.5℃)。全期正常发育温度尚可划出发育适温区(20—30℃)及最适温区(24—26℃)。在适温及最适温区,赤眼蜂的发育速率随温度的升高而稳步上升。拟澳洲赤眼蜂温度每增长5℃,发育速率增长21—23%。在最适温区或适温区下繁殖,生长发育最好,羽化率最高。在适温区以外,赤眼蜂的生长发育较大幅度地向不利方向变化,发育时间延长,发育速率减慢。赤眼蜂个体发育所需的时间十分悬殊,影响因素有接蜂时间、寄生量、卵粒大小及质量以及气候环境等。拟澳洲赤眼蜂的发育始点为10.6℃,有效积温为157日度;舟蛾赤眼蜂为9.6℃及176日度。 赤眼蜂群体羽化的时间,在自然环境下以日间为多,并受光线的影响常在晨间形成羽化高蜂。在适温下群体羽化的时间-数量关系呈主蜂前移的波形曲线。群体羽化过程一般常有三个明显的周期,形成三个羽化高峰;同一群体,每一周期的羽化高峰,在时间上常有同步现象。有97%以上的个体在三个羽化周期内完成羽化。第一周期内羽化的个体是群体中生活力最强的个体。     

人工补充寄主卵对松林内卵蜂种群消长的影响

在不同生境的松林中,人工补充寄主卵都能提高寄生效果。但林地生境不同,寄生率有明显差异。在松阔混交林中补充寄主,其寄生率比对照提高5.5—16.2倍。植被稀疏的纯松林效果较差,补充的寄生率比对照提高3.0倍。 卵蜂种群消长随季节温度而变化,全年以5月中旬至6月下旬和9月中旬至10月中旬为两个寄生高峰。卵蜂种群与松毛虫种群的消长存在较明显的相依关系,卵蜂种群随着松毛虫种群的消长而消长。施药对卵蜂种群有较大影响,施药区比对照区的寄生率约降低一倍。在混交林中填充寄主卵,能促进卵蜂种群世代延续。在逐步改善林地生境的基础上,利用人工补充寄主,可以代替人工繁蜂放蜂。