叶绿体小分子量热激蛋白介绍

本文对叶绿体小分子量热激蛋白的研究进行了简要的回顾和总结.叶绿体小分子量热激蛋白是热激蛋白超家族的成员,具有3个特殊的保守区域;当植物遇到热胁迫时,叶绿体小分子量热激蛋白能够保护光合系统Ⅱ和类囊体膜;初步分析了叶绿体小分子量热激蛋白与植物的耐热性和耐冷性关系以及其分子伴侣功能.     

High transmission of paternal plastid DNA in alfalfa plants demonstrated by restriction fragment polymorphic analysis

Summary A high frequency of paternal plastid transmission occurred in progeny from crosses among normal green alfalfa plants. Plastid transmission was analyzed by hybridization of radiolabeled alfalfa plastid DNA (cpDNA) probes to Southern blots of restriction digests of the progeny DNA. Each probe revealed a specific polymorphism differentiating the parental plastid genomes. Of 212 progeny, 34 were heteroplastidic, with their cpDNAs ranging from predominantly paternal to predominantly maternal. Regrowth of shoots from heteroplasmic plants following removal of top growth revealed the persistence of mixed plastids in a given plant. However, different shoots within a green heteroplasmic plant exhibited paternal, maternal, or mixed cpDNAs. Evidence of maternal nuclear genomic influence on the frequency of paternal plastid transmission was observed in some reciprocal crosses. A few tetraploid F₁ progeny were obtained from tetraploid (2n=4x=32) Medicago sativa ssp. sativa x diploid (2n=2x=16) M. sativa ssp. falcata crosses, and resulted from unreduced gametes. Here more than the maternal genome alone apparently functioned in controlling plastid transmission. Considering all crosses, only 5 of 212 progeny cpDNAs lacked evidence of a definitive paternal plastid fragment.Contribution No. 89-524-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan     

Generation of heteroplastidic Nicotiana cybrids by protoplast fusion: analysis for plastid recombinant types

Summary Protoplasts of a mutant line of Nicotiana tabacum having a maternally-transmitted chlorophyll deficiency were fused with protoplasts of two alloplasmic-male-sterile Nicotiana lines by the donor-recipient technique. In both fusion experiments variegated plantlets were regenerated which were shown to contain cytoplasms of mixed chloroplast nature. This confirms that with the donor-recipient method one can obtain mixed cytoplasms of genetically different chloroplasts. We present a convenient system to assay for genetic recombination between chloroplasts by combining use of several cytoplasmic markers: vis. chlorophyll pigmentation, chloroplast DNA restriction patterns, tentoxin resistance and male sterility. Within the limits of the experiment no recombinant types were recovered.     

Protein import into chloroplasts

Three proteins from the chloroplastic outer envelope membrane and four proteins from the inner envelope membrane have been identified as components of the chloroplastic protein import apparatus. Multiple molecular chaperones and a stromal processing peptidase are also important components of the import machinery. The interactions of these proteins with each other and with the precursors destined for transport into chloroplasts are gradually being described using both biochemical and genetic strategies. Homologs of some transport components have been identified in cyanobacteria suggesting that at least some of import machinery was inherited from the cyanobacterial ancestors that gave rise to chloroplasts.     

Phylogeography of the component species of broad-leaved evergreen forests in Japan,based on chloroplast DNA variation

In order to elucidate the past distribution and colonization routes of broad-leaved evergreen (lucidophyllous) forests, we investigated the intraspecific phylogeographic patterns of lucidophyllous forests in Japan and surrounding areas. We selected 6 component species with a similar geographic distributions growing in Castanopsis-dominant forests. We defined possible important refugia during the glacial periods as the regions rich in rare haplotypes (with a frequency of 5% or less), or as regions rich in the number of common haplotypes (with a frequency of more than 5%). We then located the sites of refuge by comparing the intraspecific phylogeographic patterns among 6 component species of lucidophyllous forests with respect to these two parameters (i.e., haplotype uniqueness and the number of haplotypes). The following results were obtained during the course of this study: (1) rare haplotypes were distributed among islands around the main islands of Japan; (2) rare subtypes and the greatest numbers of common haplotypes were observed in Kyushu, a finding which agreed with fossilized pollen data demonstrative of the past existence of refugia in southern Kyushu; and (3) rare haplotypes were found on the Muroto Peninsula, and the second greatest numbers of common haplotypes were observed on the Kii Peninsula, a finding which suggested the existence of additional important refugia along the Pacific coast of Japan during the glacial ages.     

Adaptive modifications of the photosynthetic apparatus in Euglena gracilis Klebs exposed to manganese excess

Summary. Asynchronous cultures of wild-type Euglena gracilis were tested for their morphophysiological response to 10mM MnSO₄. Growth was only moderately slowed (15%), while oxygen evolution was never compromised. Inductively coupled plasma analyses indicated that the Mn cell content doubled with respect to controls, but no signs of localised accumulation were detected with X-ray microanalysis. Evident morphological alterations were found at the plastid level with transmission electron microscopy and confocal laser scanning microscopy. An increase in the plastid mass, accompanied by frequent aberrations of chloroplast shape and of the organisation of the thylakoid system, was observed. These aspects paralleled a decrease in the molar ratio of chlorophyll a to b and an increase in the fluorescence emission ratio of light-harvesting complex II to photosystem II, the latter evaluated by in vivo single-cell microspectrofluorimetry. These changes were observed between 24 and 72h of treatment. However, the alterations in the pigment pattern and photosystem II fluorescence were no longer observed after 96h of Mn exposure, notwithstanding the maintenance of the large plastid mass. The response of the photosynthetic apparatus probably allows the alga to limit the photooxidative damage linked to the inappropriately large peripheral antennae of photosystem II. On the whole, the resistance of Euglena gracilis to Mn may be due to an exclusion–tolerance mechanism since most Mn is excluded from the cell, and the small amount entering the organism is tolerated by means of morphophysiological adaptation strategies, mainly acting at the plastid level.Correspondence and reprints: Dipartimento delle Risorse Naturali e Culturali, Università degli Studi di Ferrara, Corso Porta Mare 2, 44100 Ferrara, Italy.     

The development and evaluation of consensus chloroplast primer pairs that possess highly variable sequence regions in a diverse array of plant taxa

Although universal or consensus chloroplast primers are available, they are limited by their number and genomic distribution. Therefore, a set of consensus chloroplast primer pairs for simple sequence repeats (ccSSRs) analysis was constructed from tobacco (Nicotiana tabacum L.) chloroplast sequences. These were then tested for their general utility in the genetic analysis of a diverse array of plant taxa. In order to increase the number of ccSSRs beyond that previously reported, the target sequences for SSR motifs was set at A or T (n 7) mononucleotide repeats. Each SSR sequence motif, along with ±200-bp flanking sequences from the first of each mononucleotide base repeat, was screened for homologies with chloroplast DNA sequences of other plant species in GenBank databases using BLAST search procedures. Twenty three putative marker loci that possessed conserved flanking sequence spans were selected for consensus primer pair construction using commercially available computer algorithms. All primer pairs produced amplicons after PCR employing genomic DNA from members of the Cucurbitaceae (six species) and Solanaceae (four species). Sixteen, 22 and 19 of the initial 23 primer pairs were successively amplified by PCR using template DNA from species of the Apiaceae (two species), Brassicaceae (one species) and Fabaceae (two species), respectively. Twenty of 23 primer pairs were also functional in three monocot species of the Liliaceae [onion (Allium cepa L.) and garlic (Allium sativum L.)], and the Poaceae [oat (Avena sativa L.)]. Sequence analysis of selected ccSSR fragments suggests that ccSSR length and sequence variation could be useful as a tool for investigating the genetic relationships within a genus or closely related taxa (i.e., tribal level). In order to provide for a marker system having significant coverage of the cucumber chloroplast genome, ccSSR primers were strategically "recombined" and named recombined consensus chloroplast primers (RCCP) for PCR analysis. Successful amplification after extended-length PCR of 16 RCCP primer pairs from cucumber (Cucumis sativus L.) DNA suggested that the amplicons detected are representative of the cucumber chloroplast genome. These RCCP pairs, therefore, could be useful as an initial molecular tool for investigation of traits related to a chloroplast gene(s) in cucumber, and other closely related species.Communicated by C. Möllers     

A cytoplasmically inherited mutant controlling early chloroplast development in barley seedlings

Cytoplasmic line 2 (CL2) has been previously reported as a cytoplasmically inherited chlorophyll-deficient mutant selected from a chloroplast-mutator genotype of barley. It was characterized by a localized effect on the upper part of the first-leaf blade. At emergence the CL2 seedlings-phenotype varied from a grainy light green to an albino color. They gradually greened during the following days, starting from the base of the blade and extending to cover most of its surface when it was fully grown. The present results, from both light microscopy and transmission electron microscopy (TEM), confirmed the previously described positional and time-dependent expression of the CL2 syndrome along the first-leaf blade. During the first days after emergence, light microscopy showed a normally developed chloroplast at the middle part of the CL2 first-leaf blade, meanwhile at the tip only small plastids were observed. TEM showed that the shapes and the internal structure of the small plastids were abnormal, presenting features of proplastids, amyloplasts and/or senescent gerontoplasts. Besides, they lack plastid ribosomes, contrasting with what was observed inside chloroplasts from normal tips, which presented abundant ribosomes. Phenotypic observations and spectrophotometric analysis of seedlings produced by mother plants that had been grown under different temperatures indicated that higher temperatures during seed formation were negatively associated with pigment content in CL2 seedlings. In contrast, higher temperatures during the growth of CL2 seedlings have been associated with increased pigment content. Aqueous solution with kanamycin and streptomycin, which are antibiotics known to interfere with plastid gene translation, were used for imbibition of wild-type and CL2 seeds. Antibiotic treatments differentially reduced the chlorophyll content in the upper part of the first-leaf blade in CL2, but not in wild-type seedlings. These results suggest that in the wild-type, plastid-gene proteins which are necessary for chloroplast development and chlorophyll synthesis in the upper part of the first-leaf blade are usually synthesized during embryogenesis. However, under certain circumstances, in CL2 seedlings, they would be synthesized after germination. In addition, a shortening of the sheath has been observed in association with pigment decrease suggesting the existence of plastid factors affecting the expression of some nuclear genes. We consider the CL2 mutant a unique experimental material useful to study biological phenomena and external factors regulating plastid, and nuclear gene expression during embryogenesis and early seedling development.Communicated by R. Hagemann     

Intraspecific sequence variation of chloroplast DNA among the component species of evergreen broad-leaved forests in Japan

For the purpose of phylogeographic study of lucidophyllous (evergreen broad-leaved) forests in Japan, we surveyed intraspecific chloroplast DNA (cpDNA) variation in 41 component species of such forests. Intraspecific cpDNA variations were detected in 14 species. In 15 species and one species group, 16 non-coding cpDNA regions were examined to find intraspecific sequence variation. The extent of variation in these regions was compared. The largest amount of intraspecific variation was detected in the rps16 region. A relatively large amount of intraspecific variation was detected in the petD-rpoA, rpl16, and trnL-F regions. It is suggested that these regions of cpDNA would be useful for detecting intraspecific variation in plant species, and could provide valuable information for various research purposes.