植物叶片的消荧光现象

实验观察表明,非生物体有消荧光现象,生物体也有消荧光现象.它是激光与物体表面非线性相互作用的结果.植物叶片的消荧光现象是一个多光子过程,并且荧光消失过程伴随二次谐波产生.荧光消失过程中,荧光能量部分地转换为二次谐波信号,经粗略计算,转换效率大约为2.2％.     

Loss of plasma membrane lipid asymmetry can induce ordered domain (raft) formation

In some cases, lipids in one leaflet of an asymmetric artificial lipid vesicle suppress the formation of ordered lipid domains (rafts) in the opposing leaflet. Whether this occurs in natural membranes is unknown. Here, we investigated this issue using plasma membrane vesicles (PMVs) from rat leukemia RBL-2H3 cells. Membrane domain formation and order was assessed by fluorescence resonance energy transfer and fluorescence anisotropy. We found that ordered domains in PMVs prepared from cells by N-ethyl maleimide (NEM) treatment formed up to ～37°C, whereas ordered domains in symmetric vesicles formed from the extracted PMV lipids were stable up to 55°C, indicating the stability of ordered domains was substantially decreased in intact PMVs. This behavior paralleled lesser ordered domain stability in artificial asymmetric lipid vesicles relative to the corresponding symmetric vesicles, suggesting intact PMVs exhibit some degree of lipid asymmetry. This was supported by phosphatidylserine mislocalization on PMV outer leaflets as judged by annexin binding, which indicated NEM-induced PMVs are much more asymmetric than PMVs formed by dithiothreitol/paraformaldehyde treatment. Destroying asymmetry by reconstitution of PMVs using detergent dilution also showed stabilization of domain formation, even though membrane proteins remained associated with reconstituted vesicles. Similar domain stabilization was observed in artificial asymmetric lipid vesicles after destroying asymmetry via detergent reconstitution. Proteinase K digestion of proteins had little effect on domain stability in NEM PMVs. We conclude that loss of PMV lipid asymmetry can induce ordered domain formation. The dynamic control of lipid asymmetry in cells may regulate domain formation in plasma membranes.     

Effect of cations on the linear dichroism and selective polarized light scattering of thylakoids

The effect of cations on the linear dichroism (LD) and selective polarized light scattering of higher plant thylakoids was investigated. The results show that the major change in LD signal caused by the addition of cations is due to a scattering contribution most probably resulting from thylakoid stacking. However, minor changes in the LD signal also occur on the short wavelength side of the main LD band that persist even when a large proportion of the scattering change is eliminated by increasing the refractive index of the medium. The minor changes appear to be correlated with the cation-induced increase in variable fluorescence and resolution of the spectra at 77 K reveals that the changes in dichroism are due to LD bands of pigments associated with the light-harvesting complex.     

Fibrin gel enhanced trilayer structure in cell-cultured constructs

Efficient cell seeding and subsequent support from a substrate ensure optimal cell growth and neotissue development during tissue engineering, including heart valve tissue engineering. Fibrin gel as a cell carrier may provide high cell seeding efficiency and adhesion property, improved cellular interaction, and structural support to enhance cellular growth in trilayer polycaprolactone (PCL) substrates that mimic the structure of native heart valve leaflets. This cell carrier gel coupled with a trilayer PCL substrate may enable the production of native-like cell-cultured leaflet constructs suitable for heart valve tissue engineering. In this study, we seeded valvular interstitial cells onto trilayer PCL substrates with fibrin gel as a cell carrier and cultured them for 1 month in vitro to determine if this gel can improve cell proliferation and production of extracellular matrix within the trilayer cell-cultured constructs. We observed that the fibrin gel enhanced cellular proliferation, their vimentin expression, and collagen and glycosaminoglycan production, leading to improved structure and mechanical properties of the developing PCL cell-cultured constructs. Fibrin gel as a cell carrier significantly improved the orientations of the cells and their produced tissue materials within trilayer PCL substrates that mimic the structure of native heart valve leaflets and, thus, may be highly beneficial for developing functional tissue-engineered leaflet constructs.     

水分胁迫下的大豆叶取向

通过大田及盆栽实验,初步探讨了植株水分状况对大豆叶取向运动的影响。大豆末端小叶在木质部水势约为-9.1×10~5Pa时,开始呈直立状态,且大水势下降到-14.4×10~5Pa时开始发生倒位现象。随着水分胁迫加剧(超过两个临界值),大比例的末端小叶发生上述两种现象。中午木质部水势与叶片角有显著相关性。实质上,水分胁迫有诱导并加剧避日性叶取向的作用。干旱植株在复水后不到2个小时,其叶取向便可逆转。大豆叶片避日性取向通过降低接收辐射可防止叶温升高和木质部水势的下降.高度避日态并不影响叶片净光合率。     

Enhanced masking response to light in hamsters with IGL lesions

Syrian hamsters with intergeniculate leaflet or sham lesions were given tests with a series of light pulses of gradually decreasing intensities. The light pulses were given early in the night, at zeitgeber time 14–15. The amount of wheel running during the pulses was compared to that in the same hour on a night with no light pulses. Hamsters with intergeniculate leaflet lesions showed a significantly greater suppression of their wheel running in response to light than the sham-lesioned animals. The lesioned animals also had larger negative phase angles of entrainment to the 14:10-h light-dark cycle than sham-operated controls. However, phase shifting in response to light pulses at either zeitgeber time 14 or 18 was not significantly altered by the lesions. Preferences for spending more time in a dark than a light area were not abolished by the lesions. It is concluded that the intergeniculate leaflet in the Syrian hamster cannot be of paramount importance for masking of locomotor activity by light but may play a modulating role. Accepted: 30 January 1999     

Leaflet Movement of Robinia pseudoacacia in Response to a Changing Light Environment

Diurnal and nocturnal leaflet movement of black locust （Robinia pseudoacacia L.） was investigated under three light schemes： 100% natural irradiance, 50% shading, and 90% shading. Changes in leaf mid-vein angle were described by measurements of two planes： （i） β, the angle formed by the bottom of the petiolule and its relation to the horizontal plane; and （ii） θ, the angle between the petiolule and the main leaflet vein. The two highest light regimens had a significant effect on β. Variation in β tends to make the leaflet more erect, thereby minimizing any negative impact of high irradiance on leaf lamina. Light-dark rhythms induced variation in θ （termed nyctinastic movement）. Nyctinastic movement is important during the low light levels experienced by leaflets in early morning and late afternoon. At low light levels, the leaflet stopped nyctinastic movement and θ was fixed at an angle that may have enabled the leaf lamina to maximize light interception. After the light-dark cycle was reestablished, nyctinastic movement was restored. Taken together, our results suggest that irradiance induces variation in β leading to diurnal leaflet movement （diaheliotropism）, whereas the light-dark cycle influences θ, which results in nocturnal leaflet movement. Both angles are important for describing patterns of leaf movement in R. pseudocacia.     

The bioclimatological leaflet as a means conveying climatological information to tourists and the tourism industry

Climate is an important resource for tourism and must be taken into account in tourism promotions. Here, a climate leaflet containing climatological and bioclimatological information for tourists is presented. The bioclimatological conditions are portrayed using mean values and frequency of thermal sensation based on physiologically equivalent temperature for 10-day intervals covering the whole year, along with air and sea temperature, sunshine duration, amount and number of days with precipitation and wind roses. In addition, the Climate Tourism Information Scheme is included. When combined with climatological and bioclimatological conditions, this scheme is valuable for tourists as it enables them to choose the most suitable time period for holidays, with the choice depending on personal preferences and requirements. The information provided here assists the tourism industry and stakeholders in decision-making. As an example, the bioclimatological leaflet for Hvar, an island off the Croatian Adriatic coast, is presented.     

Neuropeptide Y microinjected into the suprachiasmatic region phase shifts circadian rhythms in constant darkness

The geniculohypothalamic tract (GHT) is a projection from the intergeniculate leaflet to the suprachiasmatic nucleus (SCN). The GHT exhibits neuropeptide Y (NPY) immunoreactivity and appears to communicate photic information to the SCN. Microinjection of NPY into the SCN has been found to phase shift circadian rhythms of hamsters housed in constant light in a manner similar to the phase shifts produced by pulses of darkness or triazolam injections. In the present study, NPY was injected into the SCN of Syrian hamsters housed in constant darkness and was found to produce phase shifts similar to those seen in hamsters housed in constant light. Microinjections were not followed by wheel running during the subjective day (the time when NPY microinjections are followed by significant phase advances). These data suggest that NPY produces phase shifts by some mechanism other than by inducing wheel running or by inhibiting the response of SCN neurons to light and supports a role for NPY in nonphotic shifting of the circadian clock.