飞机草花蕾中Beclin1基因的克隆与表达

本文以入侵植物飞机草的不同时期花蕾为材料,利用RT-PCR法扩增得到了与PCD相关的类Beclin1基因的部分cDNA序列(大约700bp),与烟草叶片中的基因序列（AY701316）同源性为95%;Northern blotting结果表明类Beclin1基因在花蕾发育中期的表达量高于初期和后期;通过DNA ladder检测表明在花蕾发育过程中伴随着PCD的发生,这些结果表明花蕾发育中期是PCD初期发生的活跃期,是绒毡层逐渐退化和花粉不断形成的过程。通过对生殖过程中的细胞程序性死亡的分子生物学研究,初步揭示了飞机草入侵过程与PCD的相互关系。     

飞机草花蕾中Beclin1基因的克隆与表达

以入侵植物飞机草的不同时期花蕾为材料,利用RT-PCR法扩增得到了与PCD相关的类Beclin1基因的部分cDNA序列(大约700 bp),与烟草叶片中的基因序列(AY701316)同源性为95%;Northern blotting结果表明类Beclin1基因在花蕾发育中期的表达量高于初期和后期;通过DNA ladder检测表明在花蕾发育过程中伴随着PCD的发生,这些结果表明花蕾发育中期是PCD初期发生的活跃期,是绒毡层逐渐退化和花粉不断形成的过程.通过对生殖过程中的细胞程序性死亡的分子生物学研究,初步揭示了飞机草入侵过程与PCD的相互关系.     

A light and electron microscopy analysis of the events leading to male sterility in Ogu-INRA CMS of rapeseed (Brassica napus)

Ogura cytoplasmic male sterility (CMS) occurs naturally in radishand has been introduced into rapeseed (Brassica napus) by protoplastfusion. As with all CMS systems, it involves a constitutivelyexpressed mitochondrial gene which induces male sterility tootherwise hermaphroditic plants (so they become females) anda nuclear gene named restorer of fertility that restores pollenproduction in plants carrying a sterility-inducing cytoplasm.A correlative approach using light and electron microscopy wasapplied to define what stages throughout development were affectedand the subcellular events leading to the abortion of the developingpollen grains upon the expression of the mitochondrial protein.Three central stages of development (tetrad, mid-microsporeand vacuolate microspore) were compared between fertile, restored,and sterile plants. At each stage observed, the pollen in fertileand restored plants had similar cellular structures and organization.The deleterious effect of the sterility protein expression startedas early as the tetrad stage. No typical mitochondria were identifiedin the tapetum at any developmental stage and in the vacuolatemicrospores of the sterile plants. In addition, some strikingultrastructural alterations of the cell's organization werealso observed compared with the normal pattern of development.The results showed that Ogu-INRA CMS was due to premature celldeath events of the tapetal cells, presumably by an autolysisprocess rather than a normal PCD, which impairs pollen developmentat the vacuolate microspore stage, in the absence of functionalmitochondria. Key words: Brassica napus, cell death, light and electron microscopy, mitochondria, plastids, pollen development, Ogu-INRA cytoplasmic male sterility, transgenic-restored plants, tapetum Received 30 September 2007; Revised 11 December 2007 Accepted 20 December 2007     

Programmed cell death in plant reproduction

Reproductive development is a rich arena to showcase programmed cell death in plants. After floral induction, the first act of reproductive development in some plants is the selective killing of cells destined to differentiate into an unwanted sexual organ. Production of functional pollen grains relies significantly on deterioration and death of the anther tapetum, a tissue whose main function appears to nurture and decorate the pollen grains with critical surface molecules. Degeneration and death in a number of anther tissues result ultimately in anther rupture and dispersal of pollen grains. Female sporogenesis frequently begins with the death of all but one of the meiotic derivatives, with surrounding nucellar cells degenerating in concert with embryo sac expansion. Female tissues that interact with pollen undergo dramatic degeneration, including death, to ensure the encounter of compatible male and female gametes. Pollen and pistil interact to kill invading pollen from an incompatible source. Most observations on cell death in reproductive tissues have been on the histological and cytological levels. We discuss various cell death phenomena in reproductive development with a view towards understanding the biochemical and molecular mechanisms that underlie these processes.     

Guanine-type retinal tapetum in the eye of the Pacific pomfret <Emphasis Type="Italic">Brama japonica</Emphasis> (Perciformes: Bramidae)

The eye of Brama japonica, which exhibits eyeshine, contains a retinal tapetum composed of guanine. The total amounts of guanine in the eyes of two specimens measuring 19.5 and 51.4cm in standard length were 7.4 and 70.5mg, respectively, the respective retinal surface areas being 4.9 and 39.9cm². The mean guanine content was almost identical (1.5 and 1.8mg/cm², respectively). A locus tapetalis, with guanine values exceeding 2.5mg/cm², was developed in the ventrotemporal region of the retina, where it cooccurred with the area centralis. Evidence is presented that sound functional reasons exist for both the development of the locus tapetalis and its position in the retina. A plea is made for future examination of the retinae of additional pelagic and nonpelagic species for the presence and location of a locus tapetalis.     

Sporoderm development inNymphaea mexicana (Nymphaeaceae)

Mature pollen grains ofNymphaea mexicana have a verrucate proximal surface, a psilate distal surface and an anazonasulculus (encircling-sulcate aperture). The developmental events of microspores and tapetal cells were observed with TEM and SEM. Radially oriented substructural elements are seen in the microspore surface coating ofNymphaea mexicana from the early tetrad stage through the whole exine development. These elements, being the structural units of the microspore surface matrix (glycocalyx), are associated with sporopollenin precursor accumulation. In young free microspores, radially oriented elements are observed at both proximal and distal poles as a palisade between the endexine and plasmalemma.—Several points are discussed: (1) the initial and mature forms of exine substructure elements; (2) the significance of exine substructure for realisation of morphogenetic processes; (3) the ways by which verrucate and psilate sculpture patterns are developed.     

Orbicules and the ektexine are homologous sporopollenin concretions inSpermatophyta

During microsporogenesis sporopollenin becomes accumulated independently by the only two sporopollenin-producing cell types in the higher plants—the anther tapetum and the microspores—not only within the exine, but also within the orbicules. In Spermatophytes usually only a single orbicule type is found, but sometimes, e.g., inEuphorbia palustris, two different types exist within a single species. Very interestingly, most orbicules are strikingly similar in their structure, sculpture, shape and dimension to the respective ektexine: e.g., smooth sporopollenin globules are found near the totally smooth exines ofEupomatia laurina andPentaphragma sinense respectively, while inDelonix elata andEuphorbia palustris the orbicules often look like some incomplete tectum pieces. All these parallelisms can be attributed to the homologous and therefore highly similar genetic information to form sporopollenin in the sporogeneous tissue and the anther tapetum. The orbicules should be seen neither as sporopollenin storage, as sporopollenin transfer vehicle, nor as sporopollenin surplus.     

THE TAPETUM FIBROSUM IN THE EYES OF TWO SMALL WHALES

The pygmy sperm whale ( Kogia breviceps ) and the bottlenose dolphin ( Tursiops truncatus ) are equipped with a tapetum fibrosum and, with other Cetacea, are the only carnivores known to possess this typically ungulate tapetal type. Tapeta from two regions of a retina, each with a different spectral reflectance (blue and green), were found to have significantly different fibrillar diameters and inter-fibrillar spacing. When the measured values are applied to a dielectric reflector model, the predicted wavelengths agree with the observed reflectance of the flat-mounted tapeta. The spatial properties of the fibrils change progressively from the tapetal origin in the fibroblast layer to the pigment epithelium, suggesting that different wavelengths may be reflected systematically with tapetal depth. The very large number of reflecting layers characterizing these tapeta, relative to those of other carnivores, may provide for increased spectral purity and efficiency.     

The tapetum inSchizaea pectinata (Schizaeaceae) and a comparison with the tapetum inPsilotum nudum (Psilotaceae)

A combination tapetum consisting of a cellular, parietal component and a plasmodial component occurs inSchizaea pectinata. A single, tapetal initial layer divides to form an outer parietal layer which maintains its cellular integrity until late in spore wall development. The inner tapetal layer differentiates into a plasmodium which disappears after the outer exospore has developed. In the final stages of spore wall development, granular material occurs in large masses and is dispersed as small granules throughout the sporangial loculus. No tapetal membrane develops. Comparisons are drawn with the combination tapetum found inPsilotum nudum.     

Megaspore wall growth inSelaginella (Lycopodiatae)

Different stages of megaspore and megasporangial development inSelaginella argentea (Wallich)Spring,S. bigelowii Unerw., andS. kraussiana (Kze.)A. Br. have been seen and studied. Megaspore wall units give positive reactions for polysaccharides and protein in young megaspores, and become the thick and resistant wall typical of the genus only later.—Units forming the exospore and the spaces between units enlarge from widths of 5–10nm early during development up to over 200 nm at pregermination stages. The spaces enlarge first. Initially they are circular and mostly about 70 nm in diameter. Later, spaces toward the inner part of the exospore enlarge more than those near the outer surface. During pregermination, wall spaces range in size from 4 to 50 times the width of units with the larger spaces located near the inner surface. As a result the exospore would be under tension to spring outward during germination when the laesurae are lysed.—A gap in the exospore, shaped like a half-moon in polar sections, forms in equatorial and distal portions of the spore. This gap becomes enormous, three times the volume of the central space plus the mesospore, and is filled with lipids and other nutrients. Late in development, during the period of tapetal cell degeneration, the gap contents are moved into the central space and the gap is closed.—Late in development the mesospore is degraded. Its products, along with gap contents, seem to be added to the contents of the central cavity and appear as reserve storage globules. A primary wall-like endospore is formed during this period, at the inner surface of the exospore. During germination this endospore develops further at its inner surface.—Changes in the size and shape of megasporangia occur independently of the size of megaspores.Megaspore development inSelaginella. II. For first part seeMorbelli & Rowley (1993).