莴苣助细胞发育过程中钙的分布研究

用焦锑酸盐沉淀法对莴苣助细胞中的钙分布进行了观察。结果表明,开花前3天刚形成的助细胞中的钙颗粒很少:开花前2天助细胞壁中的钙颗粒增加;开花前1天助细胞珠孔端细胞壁加厚,其中积累了许多钙颗粒:开花当天助细胞珠孔端的丝状器中聚集了大量的钙颗粒。授粉后1h时两个助细胞的结构和钙分布发生差异,一个呈退化状,其中的钙颗粒明显增多,另一宿存助细胞中的钙分布与授粉前相似。去雄不授粉1天后两个助细胞均保持完好,且两助细胞中的钙分布没有明显差异,表明由花粉管引起一个助细胞中钙含量增加进而导致了助细胞退化。退化助细胞在卵细胞与中央细胞之间形成一薄层。助细胞退化后不同部位的钙颗粒呈现出与受精作用密切有关的变化:授粉后1h时,钙主要聚集在近合点端部位;授粉后2.5h卵细胞即将受精,这时许多细小的钙颗粒主要聚集在卵细胞与中央细胞之间的薄层中;授粉后4h精、卵细胞已融合,这时退化助细胞合点端的钙颗粒明显减少,而在其珠孔端又聚集了较多的钙。上述助细胞中的钙含量变化与吸引花粉管进入胚囊和促使精卵细胞融合密切有关。     

Flower form alteration by genetic transformation with the class B MADS-box genes of <Emphasis Type="Italic">Agapanthus</Emphasis><Emphasis Type="Italic">praecox</Emphasis> spp. <Emphasis Type="Italic">orientalis</Emphasis> in transgenic dicot and monocot plants

The class B genes, which belong to the MADS-box gene family, play important roles in regulating petal and stamen development in flowering plants. These genes exist in two different types termed DEF- and GLO-like genes, and the B-function is provided by heterodimers of a DEF- and a GLO-like gene product. In the present study, dicot (tobacco and lettuce) and monocot (Tricyrtis hirta) plants were transformed with the GLO-like gene of Agapanthus praecox ssp. orientalis ApGLO alone or in combination with the DEF-like gene of the same plant ApDEF. In two out of 10 transgenic tobacco plants containing ApGLO, sepals partially converted into petaloid organs. For lettuce, ray florets of four out of nine transgenic plants containing ApGLO also developed additional petaloid organs. In two out of five transgenic T. hirta plants containing both ApGLO and ApDEF, organs developed in whorl 4 showed noticeable morphological alteration: they were much longer compared with carpels of non-transgenic plants, and had purple spots overall on the surface as filaments of non-transgenic plants. No morphological alterations were observed in vegetative organs between transgenic and non-transgenic plants for all the three species. The results obtained in the present study indicate a possibility of molecular breeding for flower form alteration by genetic transformation with the class B MADS-box gene(s) of heterologous plant species.     

The role of seasonality in lettuce consumption: a case study of environmental and social aspects

Background, aim and scope  Considerable debate surrounds the assessment of the environmental impacts and the ethical justification for providing a year-round supply of fresh produce to consumers in the developed countries of northern Europe. Society is seeking environmentally sustainable supply chains which maintain the variety of fresh food on offer throughout the year. This paper compares the environmental impacts of different supply chains providing lettuce all year round to the UK and considers consumers' meanings of—and attitudes to—available options. Lettuce has been selected as a case study as its consumption has grown steadily during the last two decades and the supply chains through cold months are protected cropping in the UK and field cropping in Spain; during warm months, lettuce is sourced from field cropping in the UK. Materials and methods  Data were collected from farms supplying each of these supply chains, and life cycle assessment methodology was used to analyse a range of impacts associated with producing (from plant propagation to harvesting and post-harvest cooling) and delivering 1 kg of lettuce to a UK Regional Distribution Centre (RDC). The downstream stages (i.e. retailing, consumption and waste management) are the same regardless of the origin of the product and were omitted from the comparison. The impacts considered included potential to induce global warming and acidification as well as three inventory indicators (primary energy use, land use and water use). Qualitative data were collected in order to assess the consumer considerations of purchasing lettuce also during winter. Results  Importation of Spanish field-grown lettuce into the UK during winter produced fewer greenhouse gas (GHG) emissions than lettuce produced in UK-protected systems at that time (0.4–0.5 vs. 1.5–3.7 kg CO₂-eq/kg lettuce in RDC). Refrigerated transport to the UK was an important element of the global warming potential associated with Spanish lettuce (42.5% of emissions), whilst energy for heating dominated the results in UK-protected cultivation (84.3% of emissions). Results for acidification were more variable and no overall trends are apparent. Results from qualitative social analysis revealed complex and multidimensional meanings of freshness and suggested that the most striking seasonal variation in vegetable/salad eating was a tendency to consume more salads in the summer and more cooked vegetables in the winter, thus suggesting that in-home consumption alone cannot explain the rise in winter imports of lettuce to the UK. Discussion  UK field-grown lettuce had the lowest overall environmental impact; however, those lettuces are only available in summer, so consumers therefore need to either accept the environmental impacts associated with eating lettuce in the winter or to switch consumption to another food product in the winter. When lettuces were field-grown in Spain and then transported by road to the UK, the overall impacts were similar to the UK field lettuces. The variation within farms of the same country employing different cultivation regimes and practices was bigger than between farms of different countries. Conclusions  This paper has explored the environmental consequences of consuming lettuce year-round in the UK. Whilst recognising the small sample size, the comparative analysis of the different supply chains does suggest that seasonality can be an important variable when defining the best choice of lettuce from an environmental point of view. Recommendations and perspectives  Further studies considering more production sites and product types are required to obtain conclusions whose general validity is clear and for different types of fresh produce. A clear distinction to be made in such studies is whether crops are produced in open fields or under protection. New characterisation methods are needed for environmental impacts derived from the use of key agricultural resources such as land and water. Social studies to investigate consumer preferences and the possibility of moving to more seasonal diets should be an integral part of these studies using samples composed of both urban and rural consumers and using a mixed methodology with both quantitative and qualitative components.

莴苣胚囊细胞分离

用酶解和解剖方法分离了莴苣的卵细胞,助细胞,中央细胞和合子。莴苣子房先在酶液中酶解40～50min,然后在不含酶的分离液中用解剖针解剖子房。在解剖出的胚囊中,可看到卵细胞,两个助细胞和中央细胞的轮廓。将胚囊的合点端切破,轻轻挤压胚囊的珠孔端,四个细胞即可逸出。在最佳条件下,90min可从40个子房中分离出29个胚囊,进一步从中分离出11个卵细胞。分离出的胚囊细胞用显微操作仪收集备用。莴苣卵细胞的成功分离为进行离体受精探索创造了条件。     

Allelopathic potential of citrus fruit peel and abscisic acid-glucose ester

Aqueous methanol extracts of Citrus junos, C. unshiu and C. hassaku fruit peel inhibited the growth of the roots and hypocotyls of lettuce (Lactuca sativa L.) seedlings. Significant reductions in the root and hypocotyl growth were observed as the extract concentration increased in all bioassays. The inhibitory activity of C. junos extract on the growth of lettuce roots and hypocotyls was about 13- and 24-fold greater than that of C. unshiu and C. hassaku extracts, respectively. The concentration of abscisic acid--D-glucopyranosyl ester (ABA-GE) in fruit peel of C. junos, C. unshiu and C. hassaku was determined since ABA-GE had been found to be a possible cause of the growth inhibitory effect of C. junos. The concentration was 132, 10.6 and 5.0 µg g^–1 dry weight in C. junos, C. unshiu and C. hassaku fruit peel, respectively. Thus, there was a good correlation between ABA-GE concentrations in C. junos, C. unshiu and C. hassaku fruit peel and the inhibitory activities of their aqueous extracts, which suggests that ABA-GE may be involved in the growth inhibitory effect of C. junos, C. unshiu and C. hassaku fruit peel.     

Race non-specific resistance to Bremia lactucae

Three ways of measuring race non-specific resistance to Bremia lactucae in lettuce were studied to determine the most important components of this form of resistance. Tests were conducted on leaf discs from 4–6 wk-old plants that were quantitatively inoculated and incubated under controlled conditions. Observations were made of disease intensity, latent period and production of conidia. Inoculum concentration markedly influenced disease intensity and latent period. Cv. Iceberg exhibited race non-specific resistance and this was characterised by a longer latent period, a lower disease intensity and reduced production of conidia compared to the susceptible control cv. Cobham Green. On older, intact plants, the differences in latent period and disease intensity between cultivars were even greater. Production of conidia was a particularly good criterion for discriminating levels of resistance.     

Effects of auxin on the spatial distribution of cell division and xylogenesis in lettuce pith explants

Summary Cylinders of pith parenchyma were tissue-cultured with their opposite ends on media which differed only in content of the morphogens auxin (IAA), sucrose, or zeatin. A range of concentrations of each of these morphogens applied at one end (none at the other end) resulted in distribution patterns of cell division and xylogenesis that were attributable to interaction between inductive levels and morphogen mobility. Auxin was crucial for tracheary patterns: large tracheary elements formed by direct differentiation of pith cells near the auxin source, smaller but still roughly isodiametric tracheary elements formed after cell division, and tracheary strands developed where, presumably, auxin transport had become polarized and then canalized. Xylogenesis was confined to regions within millimeters of the auxin source, and [¹⁴C]IAA studies showed a steep logarithmic concentration gradient along the cylinder. Patterns of tracheary strands and rings revealed that the pith explants retained some polarity from the stem from which they had been excised. However, the direction of flow of applied auxin was more effective than original polarity in controlling the orientation of tracheary strands and their constituent tracheary elements. It seems that, in tissues with little or no polarity, diffusive flow of auxin gradually induces polar flow in the same direction, together with an associated bioelectric current, and that this orients the cortical microtubules that in turn determine the orientations of cell elongation and of the secondary wall banding in tracheary elements.Abbreviations IAA indoleacetic acid - NAA naphthaleneacetic acid - TIBA triiodobenzoic acid Dedicated to the memory of Professor John G. Torrey     

Further investigation on the lateral and transversal proton currents at the thylakoid membrane level by hydrogen-deuterium exchange

Energetically-coupled processes (electron flow, proton uptake and correlated pH gradient) were investigated on envelope-free chloroplasts of lettuce suspended in ¹H₂O or ²H₂O media. Study of the light-intensity and temperature dependencies of these phenomena led to the following observations: 1. At neutral pH, ²H₂O diminishes the transmembrane H⁺ gradient in strong light (chain Photosystem II + Photosystem I) but not in low light; the total H⁺ uptake is increased at all light intensities: the buffering capacity of the inner compartment is increased in heavy water, possibly through enhancement of interactions between membranous titrable groups and the aqueous phase. 2. ²H₂O does not affect the photochemical events of the redox chain, whatever the electron pathway (PSII, PSI or PSII + PSI): only thermal steps are inhibited. The diminution of the apparent quantum yield, sometimes observed, may be ascribed to the dual site of action of the artificial redox carrier (ferricyanide) then used. 3. ²H₂O does not modify the activation energy of the limiting step of the electron flow (PSII + PSI) in uncoupled (44 vs. 47 kJ · mol^?1) or — but less clearly — in coupled, i.e., ‘basal’, state (55 vs. 59 kJ · mol^?1). ²H₂O does not either change the temperature of the phase transition of the membrane (17°C) for the uncoupled flow. However, a low-temperature transition, observed only for the coupled chain, is slightly increased by ²H₂O; this thermal transition is attributed to the freezing of some bound water near the plastoquinone pool. 4. Δp²H is smaller than Δp¹H at all temperatures (PSII + PSI chain). ΔpH is quasi-constant from 0°C to 10°C, then decreases when temperature rises. ²H₂O does not change the activation energy of the dark passive H⁺ efflux, which is almost twice that of the coupled electron flow. The phase transition at low temperature suggests that the proton efflux occurs via two parallel pathways, one temperature-dependent and the other temperature-independent. Except for the increase of the internal buffering capacity, the effects of ²H₂O on the membrane conformation seem limited, as shown by the unchanged activation energies of the electron flow and of the H⁺ leakage. The null activation energy observed at low temperature emphasizes the role of the bound water in these processes; however, the different effects of ²H₂O on the transition temperatures indicate that this bound water has different properties when associated with the translocation sites or with the H⁺ leakage ones. This ‘microcompartmentation’ of the membranes is consistent with the concept of lateral pH heterogeneity we have previously suggested (de Kouchkovsky, Y., and Haraux, F. (1981) Biochem. Biophys. Res. Commun. 99, 205–212). The theoretical computations and the experimental results suggest that in the steady state, the internal pH would be several tenths of a ‘unit’ lower near the plastoquinones than near the H⁺ efflux sites (coupling factors); this difference would be increased when ²H₊ replaces ¹H⁺, owing to the lower mobility of the deuteron. It is concluded that local, and not average, pH (and ΔpH) should be considered for the understanding of the energy transduction processes.     

Adenosine triphosphate-generated transmembrane electric potential in chloroplasts

Utilizing oxonol VI as a transmembrane electric potential indicating dye, chloroplasts are shown to develop rapid transient light-induced and ATP-induced potentials. Following the large transient signal smaller steady-state potentials are maintained with either driving system. The ATP-induced potential in the dark depends upon preactivation of the light-triggered ATPase of the chloroplasts, and is inhibited by uncouplers, ionophores such as valinomycin, and energy-transfer inhibitors such as tentoxin, Dio-9 or DCCD. Nigericin increased the signal of both the light- and the ATP-induced reactions. The fact that relatively large transient membrane potentials are induced by either a dark-to-light transition or ATP in the dark provides an explanation for previously observed phenomena such as early kinetics of photophosphorylation and the ATP-induced luminescence.     

Light quality influences the polyamine content of lettuce (Lactuca sativa L.) cotyledon explants during shoot production <Emphasis Type="Italic">in vitro</Emphasis>

Light quality has previously been shown to influence morphogenesis in lettuce cotyledon explants, with white or red light promoting adventitious shoot production, and blue light inhibiting it. Endogenous polyamine (PA) concentrations were compared between explants cultured under different light qualities. Explants cultured under white or red light accumulated PAs during shoot primordia production, with a 5.6-fold increase compared to initial concentrations under white light, and 6.7-fold increase under red light. These results suggest polyamines are involved in the formation of shoot primordia. After 18 days in culture PA concentrations decreased under white light, and to a lesser extent under red light, signaling a shift in polyamine metabolism that correlates with shoot expansion, which occurs more readily under white light. Explants cultured under blue light accumulated polyamines for the first 7 days, to a level 1.3 times greater than initial values, followed by a gradual decline during the remainder of the culture period. Explants cultured under blue light also contained a greater proportion of PCA-insoluble conjugated PAs, compared to explants under white or red light, which contained greater proportions of free or PCA-soluble conjugated polyamines. The ratio of putrescine to spermidine was also different with a lower Put:Spd ratio being associated with shoot production under white or red light, and higher Put:Spd ratio being associated with culture under blue light.