LINE-1 distribution in six rodent genomes follow a species-specific pattern

L1 distribution in mammal’s genomes is yet a huge riddle. However, these repetitive sequences were already found in all chromosomic regions, and in general, they seem to be nonrandomly distributed in the genome. It also seems that after insertion and when they are not deleterious, they are always involved in dynamic processes occurring on that particular chromosomic region. Furthermore, it seems that large-scale genome rearrangements and L1 activity and accumulation are somehow interconnected. In the present study, we analysed L1 genomic distribution in Tateragambiana (Muridae, Gerbillinae), Acomys sp. (Muridae, Deomyinae), Cricetomys sp. (Nesomyidae, Cricetomyinae), Microtusarvalis (Cricetidae, Arvicolinae), Phodopus roborovskii and P. sungorus (Cricetidae, Cricetinae). All the species studied here seems to exhibit a species-specific pattern. Possible mechanisms, and processes involved in L1 distribution and preferential accumulation in certain regions are discussed.     

Effects of Water Deficits on Carbon Assimilation

This review focuses on the effects of water deficits on photosynthesisand partitioning of assimilates at the leaf level. It is nowestablished that the rate of CO₂ assimilation in the leavesis depressed at moderate water deficits, mostly as a consequenceof stomatal closure. In fact, depending on the species and onthe nature of dehydration, carbon assimilation may diminishto values close to zero without any significant decline in mesophyllphotosynthetic capacity. This remarkable resistance of the photosyntheticapparatus to water deficits became apparent after the measurementof photosynthesis at saturating CO₂ concentrations was madepossible. Whenever light or heat stress are superimposed a declinein mesophyll photosynthesis may occur as a result of a ‘down-regulation’process, which seems to vary among genotypes. A major secondaryeffect of dehydration on photosynthetic carbon metabolism isthe change in partitioning of recently fixed carbon towardssucrose, which occurs in a number of species in parallel tothe increase in starch breakdown. This increase in compoundsof low molecular weight may contribute to an osmotic adjustment.Controlling mechanisms involved in this process deserve furtherinvestigation. Key words: Carbohydrates, carbon partitioning, heat stress, photoinhibition, photosynthetic capacity, stomatal limitation, water deficits     

Projected changes in elevational distribution and flight performance of montane Neotropical hummingbirds in response to climate change

The hovering flight of hummingbirds is one of the most energetically demanding forms of animal locomotion and is influenced by both atmospheric oxygen availability and air density. Montane Neotropical hummingbirds are expected to shift altitudinally upwards in response to climate change to track their ancestral climatic regime, which is predicted to influence their flight performance. In this study, we use the climate envelope approach to estimate upward elevational shifts for five Andean hummingbird species under two climate change scenarios. We then use field‐based data on hummingbird flight mechanics to estimate the resulting impact of climate change on aerodynamic performance in hovering flight. Our results show that in addition to significant habitat loss and fragmentation, projected upwards elevational shifts vary between 300 and 700 m, depending on climate change scenario and original mean elevation of the target species. Biomechanical analysis indicates that such upwards elevational shifts would yield a～2–5° increase in wing stroke amplitude with no substantial effect on wingbeat frequency. Overall, the physiological impact of elevational shifts of <1000 m in response to climate change is likely to be small relative to other factors such as habitat loss, changes in floristic composition, and increased interspecific competition.     

The effect of water stress on photosynthetic carbon metabolism in four species grown under field conditions

Abstract. The effect of gradually-developing water-stress has been studied in Lupinus albus L., Helianthus annuus L., Vitis vinifera cv. Rosaki and Eucalyptus globulus Labill. Water was withheld and diurnal rhythms were investigated 4–8d later, when the predawn water deficit was more negative than in watered plants, and the stomata closed almost completely early during the photoperiod. The contribution of ‘stomatal’ and ‘non-stomatal’ components to the decrease of photosynthetic rate was investigated by (1) comparing the changes of the rate of photosynthesis in air with the changes of stomatal conductance and (2) measuring photosynthetic capacity in saturating irradiance and 15% CO₂. Three species (lupin, eucalyptus and sunflower) showed larger changes of stomatal conductance than photosynthesis in air, and showed little or no decrease of photosynthetic capacity in saturating CO₂. Photosynthesis in air also recovered fully overnight after watering the plants in the evening. In grapevines, stomatal conductance and photosynthesis in air changed in parallel, there was a marked decrease of photosynthetic capacity, and photosynthesis and stomatal conductance did not recover overnight after watering water-stressed plants. Relative water content remained above 90% in grapevine. We conclude that non-stomatal components do not play a significant role in lupins, sunflower or eucalyptus, but could in grapevine. The effect of water-stress on partitioning of photosynthate was investigated by measuring the amounts of sucrose and starch in leaves during a diurnal rhythm, and by measuring the partitioning of ¹⁴C-carbon dioxide between sucrose and starch. In all four species, starch was depleted in water-stressed leaves but sucrose was maintained at amounts similar to, or higher than, those in watered plants. Partitioning into sucrose was increased in lupins and eucalyptus, and remained unchanged in grapevine and sunflower. It is concluded that water-stressed leaves in all four species maintain high levels of soluble sugars in their leaves, despite having lower rates of field photosynthesis, decreased rates of export, and low amounts of starch in their leaves.     

ABA xylem concentrations determine maximum daily leaf conductance of field-grown Vitis vinifera L. plants

Differences in maximum leaf conductance in grapevine plants growing in soils with contrasting water availabilities during mid-summer in Portugal could be accounted for by differences in the concentration of ABA in xylem sap. This conclusion is reinforced by the observation that the relationship between leaf conductance and endogenous ABA concentration can be mimicked by the application of exogenous ABA to leaves detached from irrigated plants. During the day, leaf conductance decreased after a morning peak, even when the leaves remained in a constant environment at a moderate temperature and leaf-to-air vapour pressure difference. This decline in leaf conductance was not a consequence of an increase in the xylem ABA concentration or the rate of delivery of this compound by the transpiratory stream. The afternoon depression in leaf conductance was associated with an apparent limitation in stomatal opening potential, which persisted even when detached leaves were fed with water and rehydrated. The reason for this inhibition has still to be identified.     

Water Stress, CO2 and Climate Change

Climatic change may bring about increased aridity to large areasof Europe. Higher temperatures, larger water deficits and highlight stress are likely to occur in conjunction with elevatedatmospheric CO₂. This raises the question whether a high CO₂concentration in the atmosphere can compensate for the decreasein carbon gain in water-stressed plants. The processes whichdetermine dry matter production and the ways they are affectedby soil water deficits are discussed. It is now well establishedthat in most species and under most circumstances stomata arethe main limiting factor to carbon uptake under water deficit,the photosynthetic machinery being highly resistant to dehydration.However, when other stresses are superimposed, a decline inphotosynthetic capacity may be observed. In the short term,under drought conditions, the increase in CO₂ in the atmospheremay diminish the importance of stomatal limitation for carbonassimilation, inhibit photorespiration, stimulate carbon partitioningto soluble sugars and increase water-use efficiency. Some recentevidence seems to indicate that under conditions of high irradiance,plants growing at elevated CO₂ may develop protection towardsphotoinhibition, which might otherwise result in significantlosses in plant production under stress conditions. In the longerterm though, a negative acclimation of photosynthesis appearsto occur in many species, an explanation for which still needsto be clearly identified. Similarly, the effects of extendedexposure to elevated CO₂ under arid conditions are not known.Plant production is more closely related to the integral ofphotosynthesis over time and total foliage area than to theinstantaneous rates of the photosynthetic process. Water deficitsresult in a decrease in foliage area biomass and, therefore,in productivity. On the other hand, the increase in air temperaturemay result in more respiratory losses. However, experimentalas well as simulatory evidence suggests that doubling CO₂ concentrationin the air may improve carbon assimilation and compensate partiallyfor the negative effects of water stress even if we assume adown-regulation of the photosynthetic process as a result ofacclimation to elevated CO₂.     

Afternoon Depression In Photosynthesis in Grapevine Leaves--Evidence for a High Light Stress Effect

A midday depression in net photosynthesis and in stomatal conductancewas observed when leaves of well-watered Vitis vinifera plantswere subjected to a diurnal pattern of variation in leaf temperatureand leaf-to-air water vapour pressure difference similar toa summer day, while photon flux density was kept constant at1450 µmolm^–2 s^–1,. When leaves were kept atconstant leaf temperature (22.5°C) and leaf-to-air watervapour presure difference (8.5 Pa kPa^–1) at the same lightintensity, stomata opened with the onset of illumination andmaximal conductance and photosynthesis values were observedabout 1 h later. Subsequently, conductance and photosynthesisdecreased gradually. Leaf water potential never dropped below{macron}0.3 MPa. Leaves kept under constant environmental conditionsshowed an afternoon decline in photosynthesis at high internalCO₂, in carboxylation efficiency and in maximum conductanceas well as an increase in stomatal sensitivity to CO₂. Whenthe photon flux density during the day was reduced to 750 µmolm^–2 s^–1, the afternoon depression in gas exchangerates was attenuated. To evaluate the possible effects of highlight stress on changes in chloroplastic behaviour we comparedlight response curves of photosynthesis determined with an oxygenelectrode, in the morning and in the afternoon after the plantswere exposed to either high or moderate photon flux densities.A significant depression in photosynthetic capacity was foundby this method in high light treated leaves, but not in leavespreviously exposed to moderate photon flux density. Apparentquantum yield decreased in the afternoon, particularly afterexposure to high light. Maximum chlorophyll a fluorescence at22°C was reduced and the quenching of fluorescence afterreaching the peak was slower in the afternoon than in the morning,especially in high light-treated leaves. Changes in the patternsof chlorophyll fluorescence kinetics were observed after lighttreatment, i.e. in the afternoon, with oscillations either absent(after high light) or significantly reduced (after moderatelight) in comparison to the morning. The significance of theseresults is discussed and it is suggested that a direct inhibitoryeffect of high light at the chloroplast level provides the bestinterpretation for the observed afternoon decline in photosyntheticrate. Key words: Carboxylation efficiency, chlorophyll fluorescence, photosynthetic capacity, quantum yield, stomatal conductance, Vitis vinifera L.     

Hemicellulosic Polysaccharides from the Xylopodium of Ocimum nudicaule: Changes in Composition in Dormancy and Sprouting

Changes in the yield and composition of hemicelluloses fromthe underground organs (xylopodia) of Ocimum nudicaule wereinvestigated. Hemicelluloses constituted about 12% of the delipidizedpowder in sprouting and about 30 % in dormant phases. Xyloseis the major component of hemicelluloses A and B (and is alsopresent in C), followed by arabinose, galactose, glucose, rhamnoseand mannose. The amounts of hemicellulose B decreased by sixtimes between dormancy and sprouting, whereas the yields ofhemicelluloses A and C remained constant. This, together withthe higher solubility of hemicellulose B and its higher susceptibilityto hemicellulase in sprouting indicates that this fraction constitutesa cell-wall bound storage polysaccharide, which may play a rolein the onset of xylopodia bud sprouting. Ocimum nudicaule, hemicelluloses, cell-wall storage polysaccharide