A Putative Calcium-Permeable Cyclic Nucleotide-Gated Channel, CNGC18, Regulates Polarized Pollen Tube Growth

A tip-focused Ca^2＋ gradient is tightly coupled to polarized pollen tube growth, and tip-localized influxes of extracellular Ca^2＋ are required for this process. However the molecular identity and regulation of the potential Ca^2＋ channels remains elusive. The present study has implicated CNGC18 （cyclic nucleotide-gated channel 18） in polarized pollen tube growth, because its overexpression induced wider and shorter pollen tubes. Moreover, CNGC18 overexpression induced depolarization of pollen tube growth was suppressed by lower extracellular calcium （[Ca^2＋]ex）. CNGC18-yellow fluorescence protein （YFP） was preferentially localized to the apparent post-Golgi vesicles and the plasma membrane （PM） in the apex of pollen tubes. The PM localization was affected by tip-localized ROP1 signaling. Expression of wild type ROP1 or an active form of ROP1 enhanced CNGC18-YFP localization to the apical region of the PM, whereas expression of RopGAP1 （a ROP1 deactivator） blocked the PM localization. These results support a role for PM-Iocalized CNGC18 in the regulation of polarized pollen tube growth through its potential function in the modulation of calcium influxes.     

The evolution of Nyctereutes (Carnivora: Canidae) in the Nihewan Basin,Hebei, northern China

The occurrence of Nyctereutes during the Plio-Pleistocene has long been reported in northern China, with the highest abundance in the Nihewan Basin. However, due to site dispersal, the coexistence of different taxa, and lack of a precise stratigraphic constraint, the evolutionary process of this genus remains enigmatic. In this study, we re-examined the available Nyctereutes materials recovered from the Nihewan Basin housed in IVPP and Tianjin Natural History Museum, in addition to a newly recovered specimen from our latest excavation. Furthermore, we compared these materials with Nyctereutes fossils recovered from the Pleistocene Zhoukoudian sites near Beijing and the extant species N. procyonoides. Our analysis of the upper molar morphometry reveals the variations in size and dietary characteristics within different species of Nyctereutes during the late Plio-Pleistocene. The examination of molars indicates an increase in the size of Nyctereutes sinensis compared to early Pliocene N. tingi as well as changes in the molar teeth morphology. Subsequently, changes in diet or environmental factors possibly caused the decrease of body size in the late Pleistocene. We also estimate an age constraint for the fossils of N. sinensis from the Xiashagou section by relocating Licent's localities and referring of updated magnetostratigraphic data.     

Integrated regulation of the photosynthetic gene family from Arabidopsis thaliana in transformed tobacco cells

Summary Expression of the three chlorophyll a/b binding protein (cab) genes of Arabidopsis thaliana was studied in transformed tobacco tissues. For each cab gene, approximately 1000 bp of the promoter region plus a portion of the structural gene was inserted into a promoter-expression vector such that a translational fusion between the cab gene and the promoter-less chloramphenicol acetyltransferase (cat) gene was formed. The constructed molecules were introduced into either cultured tobacco cells or tobacco leaves and the promoter activity was monitored as chloramphenicol acetyltransferase activity. The light-grown tissues exhibited 1.5- to 60-fold greater promoter activity than did dark-grown tissues. Expression of the cab promoters was tissue specific: activities were much stronger in green leaves than other tissues. The cab promoters were almost equally active in transformed calli or shoots derived from leaves. However, in cultured tobacco cells, one promoter was two to three times stronger than the other two. The chimeric gene fusion, cab-cat, segregated in the F1 generation as a dominant Mendelian trait.     

The effect of light and phytochrome on 1-aminocyclopropane-1-carboxylic Acid metabolism in etiolated wheat seedling leaves

While light-grown wheat leaves produced ethylene at a low rate of <0.1 nanomoles per gram per hour and contained 1-aminocyclopropane-1-carboxylic acid (ACC) at low levels of <2.5 nanomoles per gram, etiolated wheat leaves produced ethylene at a rate of 2 nanomoles per gram per hour and accumulated concentrations of ACC at levels of 40 nanomoles per gram. Upon illumination of 8-day-old etiolated wheat seedlings with white light, the ethylene production rate increased initially, due to the activation of ethylene-forming activity, but subsequently declined to a low level (0.1 nanomoles per gram per hour) at the end of the 6-hour illumination. This light-induced decline in ethylene production rate resulted from a decline (more than 35 nanomoles per gram) in ACC level, which was accompanied by a corresponding increase in 1-(malonylamino)cyclopropane-1-carboxylic acid content. These data indicate that illumination promoted ACC malonylation, resulting in reduced ACC level and consequently reduced ethylene production. However, light did not cause any significant increase in the extractable ACC-malonyltransferase activity. The effect of continuous white light on promotion of ACC malonylation was also observed in intermittent white light or red light. A far-red light treatment following red light partially reversed the red light effect, indicating that phytochrome participates in the promotion of ACC malonylation.     

Three distinct regulatory elements comprise the upstream promoter region of the nopaline synthase gene

Summary Fine deletion mutants were generated in the upstream control region of the nopaline synthase (nos) promoter to define the position and role of upstream regulatory elements. The results indicated that the 8 bp sequence (CAGAAACC) at -106/-113 and its inverted repeat (GGTTTCTG) at -140/-147 are important for promoter function. The downstream element appears more important than the upstream element since deletion of the former reduced promoter activity more significantly than deletion of the latter. Deletion of the element alone, however, did not abolish promoter function, whereas, deletion of the 10 bp potential Z-DNA-forming (Z) element located between the repeat elements nullified promoter activity. Therefore, it appears that the Z element is an essential upstream regulator and the repeated elements are upstream modulators of the nos promoter. These elements are functionally distinct since alteration of stereospecificity or insertion of short oligonucleotides between the elements did not significantly influence promoter activity. These regulatory elements were unable to function from 200 bp upstream of the CCAAT-TATA box region.     

Characterization of the lipid A component of genuine smooth-form lipopolysaccharide

The smooth-form lipopolysaccharide of Salmonella abortus equi had earlier been separated into three distinct fractions, a long-chain fraction with an O chain containing 20-50 repeating units, a short-chain fraction consisting of an R lipopolysaccharide and another with 1-6 repeating units, and an R fraction identical to the lipopolysaccharide synthesized by Ra.b-mutant bacteria [Galanos et al. (1988) J. Chromatogr. 440, 397-404]. In this paper, the corresponding lipid A from each fraction was prepared by a newly elaborated procedure based on hydrolysis of the fractions in calcium acetate buffer (pH 3.5) followed by separation of the resulting free lipid A from the polysaccharide on a Sephadex G-100 column. Chemical analysis revealed that lipid A of the R fraction contained the expected spectrum and amounts of fatty acids and it proved to be structurally identical to lipid A of previously studied Salmonella R mutants. In contrast, the lipid A of the long-chain fraction contained only about 60% fatty acids compared to that of the R fraction. The lipid A of the short-chain fraction also expressed a reduced substitution pattern of acyl residues.     

小麦间期集缩染色质的超微结构研究

本文以普通小麦(Triticum aestivum L.)根端分生组织为材料,在透射电镜下对间期细胞核内的集缩染色质的高层次结构进行了研究。在其中观察到直径约为20—25nm、50nm及110—120nm 的不同等级染色线,并且发现直径110—120nm 的染色线是由50nm 的染色线组成的,而直径约50nm 的染色线是由20—25nm 的染色线组成的。对这三个层次染色质结构之间的集缩方式进行了讨论。     

虫草成熟子囊壳、子囊与子囊孢子的电镜观察

虫草子囊壳壁为拟薄壁组织,基部与子座菌丝相联,顶端有一孔口,其内无缘丝,中心腔内无侧丝,基部着生的子囊垂直平行排列。子囊顶端中央是乳状突起,围以隆起的环状膜质边缘。成熟时,其顶端乳状突起膨大,膜质边缘也随之翻卷,中央有一小孔。同一子囊壳内子囊顶端发育阶段不同,说明子囊的形成不同步。子囊内含有两条平行的具横隔的子囊孢子。虫草子囊顶端形态结构即不象虫草属模式种蛹虫草,也不象头状虫草,说明子囊顶端的形态结构的种间差异。