摘要:

AbstractThe effect of the membrane impermeant sulfhydryl group (SH) reagent, p‐chloromercuribenzenesulfonic acid (p‐CMBS), on electrical membrane transport properties of the giant alga,Chara corallina, was determined. In an external medium with a high K+concentration (5 mM) cells typically exhibited stable membrane potentials close to the K+equilibrium potential. The steady‐state current‐voltage (I‐V) relation could be dissected into two distinct components: an almost linear ohmic leak current and a voltage‐dependent K+current. Adding 0.5 mM p‐CMBS to the external medium resulted in an immediate, short depolarization transient (resembling the time course of an action potential) and was associated with a slow down of the cytoplasmic streaming velocity. The depolarization, as well as the streaming inhibition, could be abolished by pretreating cells with the Ca2+channel inhibitor, LaCl3. This suggests that the depolarization transient reflected a p‐CMBS induced Ca2+influx, a scenario known to trigger membrane excitation and slow down of cytoplasmic streaming. From the I‐V analysis it appeared that p‐CMBS also caused a reversible inhibition of two additional transmembrane currents: (1) a reduction of a leak current and (2) a modification of the deactivation kinetics of the voltage‐dependent K+channels. From the I‐V difference analysis, the inhibited leak current was identified as a K+current, because the reversal potential was close to the estimated K+equilibrium potential. Control experiments have furthermore shown that the mercapto reagent, dithiothreitol, partly reversed the effect of p‐CMBS. This strengthens the view that the action of the mercurial is related to a specific and direct modification of SH groups. The p‐CMBS‐evoked inhibition of K+currents was not abolished by the LaCl3pretreatment, which suggests that the effect of the SH reagent is not induced indirectly by p‐CMBS‐triggered Ca2+influx. Therefore, it is suggested that the mercurial interacts dir

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00240.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe thermotropic phase behaviour of tonoplast material isolated from leaf mesophyll protoplasts of the obligatory CAM plantKalanchoë daigremontianawas investigated by electron power magnetic resonance (EPR) spectroscopy using a spin label technique. The data clearly show that at temperatures below 9 °C the tonoplast membrane is in a rigid state. Above 9 °C, an increasing fluidization of the tonoplast occurs. Two distinct temperature ranges were observed: a cooperative melting process between 9 and 14 °C being followed by a second broad melting process starting at 18 °C, with continuously increasing membrane fluidity up to 51 °C, which was the highest temperature tested. These results are important for a better understanding of the mechanism of the temperature modulation of CAM. The data support the hypothesis that temperature affects CAM via the permeability of the tonoplast membrane, which determines the rates of the passive malic acid efflux from the vacuole and thus the capability of the plant to accumulate malic acid in the vacuoles overnight at a given temper

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00241.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIt is known from previous investigations that dry lichens with green algae are able to recover net photosynthesis through rehydration with water vapor, whereas all blue‐green lichens tested so far lack this ability. The REM micrographs of the present study show that the green phycobionts (Trebouxiaspec.) ofRamalina maciformisbecome turgid only after water vapor uptake. In contrast, the blue‐green phycobionts (Nostocspec.) ofPeltigera rufescensdo not differ in appearance from the dry state, even when the thallus has reached equilibrium with the water vapor‐saturated air; they require liquid water for turgidity. It is hypothesized that, after humidity hydration, water content is not sufficient for reestablishment of a functioning osmotic cell system in the blue‐green phy

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00242.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractEmploying immunogold electron microscopy, the subcellular location of the Calvin cycle enzyme phosphoribulokinase (PRK) was determined for two diverse species of microalgae. In both the red algaPorphyridium cruentumand the green algaChlamydomonas reinhardtii, PRK was distributed throughout the thylakoid‐containing chloroplast stroma. In contrast, the next enzyme in the pathway, ribulose 1,5‐bisphosphate carboxylase/oxygenase, was predominantly pyrenoid‐localized in both species. InPorphyridium, the chloroplast stroma abuts the pyrenoid but inChlamydomonasand other green algae, the pyrenoid appears encased in a starch sheath. Unique inclusions found in the pyrenoid ofChlamydomonaswere immunolabelled by anti‐PRK and thus identified as regions of chloroplast stroma. It is postulated that such PRK‐containing stromal inclusions in the pyrenoids ofChlamydomonasand perhaps other green algae provide a means for exchange of Calvin cycle metabolites between pyrenoid a

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00243.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPhotosynthetic flexibility and water use efficiency ofKalanchoë petitianaA. Rich., a facultative CAM plant endemic to the highlands of Ethiopia, were investigated to determine the physiological determinants for the ecological success of the plant. Both field measurements of δ13C and greenhouse gas exchange studies showed a shift from C3photosynthesis to CAM as leaves aged or at the onset of water stress. Recycling of CO2was observed in developing leaves without concomitant net CO2uptake. Accumulation of malate was positively correlated with increased cell sap osmolality and improved daily water use efficiency. The importance of flexibility in carbon uptake pathway and of recycling CO2for the ecological success of the plant is discusse

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00244.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractFragrance composition of flowers from 101 plant species, especially orchids, were analyzed. Several compounds, including allo‐aromadendrene, β‐bourbonene, α‐copaene, α‐cubebene, 1,2‐dimethoxybenzene, 1,3,5‐trimethoxybenzene, epoxygeranyl acetate, 7,11‐epoxymegastigma‐5(6)‐en‐9‐one, two γ‐lactones, germacradienol, germacrene D, humulene, methoxy‐phenyl‐ethyl acetate, myrcene epoxide, sabinene, styrene, and undecatriene were detected for the first time in orchids. Fragrance composition of flowers pollinated by male euglossine bee species (perfume flowers) of four plant families are compared and contrasted with those of orchid species with other pollination systems.Melittophilous, but highly specialized orchids, produce fragrances rich in different sesquiterpenes and other rare compounds. In the species that are exclusively pollinated by fragrance‐collecting male euglossine bees, the fragrances are primary attractants that serve both as an attractant and as a reward. The unusually intensely smelling flowers mostly produce esters and monoterpenes. The fragrances of euglossophilous flowers of the three plant families investigated are composed of nearly the same sets of chemical compounds, suggesting convergent evolution.Typically, euglossophilous plant species produce large amounts of few fragrant substances while melittophilous species often produc

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00245.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00246.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe pollination biology and breeding system ofVellozia squamata(Velloziaceae), a species of cerrado vegetation in Central Brazil, were studied.V. squamatais unusual in being pollinated by a few, generalist bee species despite having very large flowers, and having a distinctive pulsed flowering phenology. The species is self‐incompatible but with a late‐acting, post‐fertilization rejection mech

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00247.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo biomechanically different types of tree fork are described: the “compression fork” where the two jointed stems are pressed against each other at the contact face by the action of reaction wood, and the “tension fork” where the two connected stems are bent away from each other by gravity or wind action leading to tensile stresses in the connective zone.It is well known that trees permanently try to improve their own designs by adaptive growth in order to maintain a state of constant mechanical stress at the tree surface. In the case of these two different types of tree fork, adaptive growth also takes different ways in order to avoid high localized stress peaks which could lead to failure of the tree under wind loading.In this paper only the tension fork is assessed with respect to its shape optimization by computer simulation of adaptive growth. It is shown that the tensile fork is shape optimized in a very perfect way in order to avoid any dangerous localized stress peaks (notch stresses) which could lead to failure of t

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00248.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00249.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY