Overexpression of a NAC-domain protein promotes shoot branching in rice

For a better understanding of shoot branching in rice (Oryza sativa), a rice activation-tagging library was screened for mutations in tiller development. Here, an activation-tagging mutant Ostil1 (Oryza sativa tillering1) was characterized, which showed increased tillers, enlarged tiller angle and semidwarf phenotype. Flanking sequence was obtained by plasmid rescue. RNA-interfering and overexpression transgenic rice plants were produced using Agrobacterium-mediated transformation. The mutant phenotype was cosegregated with the reallocation of Ds element, and the flanking region of the reallocated Ds element was identified as part of the OsNAC2 gene. Northern analysis showed that expression of OsNAC2 was greatly induced in the mutant plants. Transgenic rice overexpressing the OsNAC2 resulted in recapture of the mutant phenotype, while downregulation of OsNAC2 in the Ostil1 mutant through RNA interfering (RNAi) complemented the mutant phenotype, confirming that the Ostil1 was caused by overexpression of OsNAC2. Overexpression of OsNAC2 regulates shoot branching in rice. Overexpression of OsNAC2 contributes tiller bud outgrowth, but does not affect tiller bud initiation. This suggests that OsNAC2 has potential utility for improving plant structure for higher light-use efficiency and higher yield potential in rice.     

Breaking the apple embryo dormancy by nitric oxide involves the stimulation of ethylene production

Mature seeds of apple (Mallus domestica Borb. cv. Antonówka) are dormant and do not germinate unless their dormancy is removed by several weeks of moist-cold treatment. We investigated the effect of short-term (3 h) nitric oxide (NO) pretreatment on breaking of apple embryonic dormancy expressed as inhibition of germination and morphological abnormalities of young seedlings. Imbibition of embryos isolated from dormant apple seeds with sodium nitroprusside (SNP) or S-nitroso,N-acetyl penicillamine (SNAP) as NO donors resulted in enhanced germination. Moreover, NO treatment removed morphological abnormalities of seedlings developing from dormant embryo. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-teramethylimidazoline-1-oxyl-3 oxide (cPTIO) removed the above effects. NO-mediated breaking of embryonic dormancy correlated well with enhanced ethylene production. Inhibitor of ethylene synthesis (AOA) reversed the stimulatory effect of NO donors on embryo germination. Additionally SNP reduced embryo sensitivity to exogenously applied ABA ensuing dormancy breakage. We can conclude that NO acts as a regulatory factor included in the control of apple embryonic dormancy breakage by stimulation of ethylene biosynthesis.     

Seed dormancy and germination of the European Chaerophyllum temulum (Apiaceae), a member of a trans-Atlantic genus

BACKGROUND AND AIMS: The European Chaerophyllum temulum and two North American Chaerophyllum species have a trans-Atlantic disjunct distribution. This work aimed to resolve requirements for dormancy break and germination of C. temulum seeds and to compare dormancy traits with those of the two North American congeners. METHODS: Phenology of germination and embryo growth was studied by regularly exhuming seeds sown in natural conditions. Temperature requirements for embryo growth, breaking of dormancy and germination were determined by incubating seeds under controlled laboratory conditions. Additionally the effect of GA(3) on germination was tested to determine the specific dormancy type. KEY RESULTS: In natural conditions, embryo growth starts in early winter. Seedlings emerge in late winter shortly after the embryos reached the critical ratio for embryo length to seed length (E : S) of approx. 0.95. Growth of the embryo only occurs during a prolonged incubation period at 5 degrees C. After stratification at 5 degrees C, which breaks physiological and morphological dormancy, seeds can germinate at a wide range of temperatures. GA(3) did not substitute for cold stratification in seeds placed at 23 degrees C. CONCLUSIONS: Chaerophyllum temulum has deep complex morphophysiological dormancy. This dormancy type differs considerably from that of the two North American congeners.     

Seed anatomy and water uptake in relation to seed dormancy in Opuntia tomentosa (Cactaceae, Opuntioideae)

BACKGROUND AND AIMS: There is considerable confusion in the literature concerning impermeability of seeds with 'hard' seed coats, because the ability to take up (imbibe) water has not been tested in most of them. Seeds of Opuntia tomentosa were reported recently to have a water-impermeable seed coat sensu lato (i.e. physical dormancy), in combination with physiological dormancy. However, physical dormancy is not known to occur in Cactaceae. Therefore, the aim of this study was to determine if seeds of O. tomentosa are water-permeable or water-impermeable, i.e. if they have physical dormancy. METHODS: The micromorphology of the seed coat and associated structures were characterized by SEM and light microscopy. Permeability of the seed-covering layers was assessed by an increase in mass of seeds on a wet substrate and by dye-tracking and uptake of tritiated water by intact versus scarified seeds. KEY RESULTS: A germination valve and a water channel are formed in the hilum-micropyle region during dehydration and ageing in seeds of O. tomentosa. The funicular envelope undoubtedly plays a role in germination of Opuntia seeds via restriction of water uptake and mechanical resistance to expansion of the embryo. However, seeds do not exhibit any of three features characteristic of those with physical dormancy. Thus, they do not have a water-impermeable layer(s) of palisade cells (macrosclereids) or a water gap sensu stricto and they imbibe water without the seed coat being disrupted. CONCLUSIONS: Although dormancy in seeds of this species can be broken by scarification, they have physiological dormancy only. Further, based on information in the literature, it is concluded that it is unlikely that any species of Opuntia has physical dormancy. This is the first integrative study of the anatomy, dynamics of water uptake and dormancy in seeds of Cactaceae subfamily Opuntioideae.     

银杏芽中内源激素与大小年结实的关系

为探讨银杏大、小年结实现象的生理原因,于2004～2005年,用ELISA(间接酶联免疫法)对银杏大年树和小年树果芽和叶芽内的IAA,GA,ZR和ABA含量进行了对比测定。结果表明:大年树IAA、ZR和ABA含量在果芽和叶芽之间的比值均高于小年树,GA含量在果芽和叶芽之间的比值则低于小年树,有利果芽分化生长,形成大年;果芽中较高水平的ZR、IAA和ABA与较低水平的GA,以及萌芽前期较高的IAA/GA,ZR/GA和ABA/GA等比值,有利果芽分化,形成大年;叶芽中较高的ZR、IAA和较低的ABA有利于形成大年生长,尤其是ZR含量在萌芽前期或中期升高与形成大年生长关系密切。     

观赏植物花芽分化研究进展

花芽分化是有花植物发育中最为关键的阶段,同时也是一个复杂的形态建成过程。简要综述了植物花芽分化过程中形态结构、外部因子与内部因子的影响,以及花芽分化中花转变的顺序和基因对成花的作用,并对观赏植物花芽分化的展望与问题做了概述和探讨。     

Chiroptical properties of diamino carboxylic acids

Diamino carboxylic acids have recently come to the attention of scientists working in the field of early life and its development. These are the monomers of a hypothetic early form of genetic material, the so-called Peptide Nucleic Acid (PNA) (Nielson et al., Proc Natl Acad Sci USA 2000;97:3868-3871). Since all biopolymers rely on a specific handedness of their building blocks, the question of symmetry breaking occurs in diamino acids and PNA in the same way as in amino acids and proteins. One possible mechanism for triggering this, is asymmetric photochemistry in interstellar/circumstellar matter by means of circularly polarized light (Bailey et al., Science 2005;281:672-674; Bailey, Orig Life Evol Biosphere 2001;21:167-183; Buscherm?hle, Astrophys J 2005;624:821-826; Meierhenrich, Angew Chem Int Ed Engl 2005;44:5630-5634). Here we have measured the CD-spectra of four chiral diamino carboxylic acids, three of which were found in the Murchison meteorite (Meierhenrich, Proc Natl Acad Sci USA 2004;101:9182-9186). The spectra show a uniform peak at 200 nm. These results and additional quantum mechanical calculations of the involved molecular orbitals support the assumption that the process of symmetry breaking in diamino acids does not depend significantly on the length of the side chain. This means that one process alone could suffice to lead to symmetry breaking in all four measured diamino carboxylic acids and might even to some extent be transferable to monoamino acids, the monomers of proteins.     

Secondary buds in Scots pine trees infested with <Emphasis Type="Italic">Gremmeniella abietina</Emphasis>

In winter 2000–2001, there was a serious outbreak of Gremmeniella abietina Morelet in southeastern Norway. During the outbreak, we noted that injured Scots pine trees (Pinus sylvestris L.) developed secondary buds in response to the fungus attack, and we decided to study the relationship between injury, appearance of secondary buds and recovery of the trees thereafter. For this purpose, 143 trees from 10 to 50 years of age were chosen and grouped into crown density classes. Injury was assessed in detail, and buds were counted before bud burst in the spring of 2002. In addition, a subset of 15 trees was followed through the summer of 2002 to assess recovery. All injured trees developed secondary buds, with a clear overweight of dormant winter buds in proportion to interfoliar buds. Healthy control trees did not develop secondary buds at all. The secondary buds appeared predominantly on the injured parts of the tree; interfoliar buds in particular developed just beneath the damaged tissue. Most of the secondary buds died during the winter of 2001–2002, mainly because the fungus continued to spread after the first outbreak. Many of the remaining buds developed shoots with abnormal growth during the summer. Secondary buds may help trees to recover from Gremmeniella attacks, but this strategy may fail when the fungus continues to grow and injure the newly formed buds and shoots.