摘要:

Abstract.The effect of climatic warming on the timing of bud burst and the subsequent risk of frost damage on trees in central Finland was assessed with the aid of a computer model, 73 years of temperature data and a climatic scenario corresponding to doubled level of atmospheric CO2. In general, climatic warming hastened bud burst, due to ontogenetic development during warm spells in autumn, winter and spring. During the years with the warmest winters in the scenario conditions: (a) bud burst took place during mid‐winter; and (2) depending on the year, the trees were subsequently exposed to temperatures between −27 and −10°C. This finding suggests that the risk of frost damage to trees will be increased if the predicted climatic warming occurs. Because of the assumptions used in the model, the results are not conclusive, but they do point out the importance of further experimental studies on genetic and environmental regulation of timing of bud burst in

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01514.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.An Ohm's law analogy is frequently employed to calculate parameters of leaf gas exchange. For example, resistance to water vapour loss is calculated as the quotient of vapour pressure difference (VPD) and vapour loss by transpiration. In the present research, this electrical analogy was extended. Steady‐state transpiration as a function of VPD, assayed in leaflets ofVicia fabausing gas exchange techniques, was compared with steady‐state K+current magnitude as a function of voltage in isolated guard cell protoplasts ofVicia faba, assayed using the patch clamping technique in the whole cell configuration. An electrophysiological model originally developed to explain the kinetics of current changes following step changes in voltage across a cell membrane was used to fit the kinetics of transpiration changes following step changes in VPD applied to leaflets ofVicia faba.Following step increases in VPD, transpiration exhibited an initial increase, reflecting the increased driving force for water loss and, for large step increases in VPD, a transient decrease in stomatal resistance. Transpiration subsequently declined, reflecting stomatal closure. By analogy to electrophysiological responses, it is hypothesized that the humidity parameter that is sensed by guard cells is VPD. Two models based on epidermal water relations were also applied to transpiration kinetics. In the first model, the transient increase in transpiration following a step increase in VPD was attributed partially to an increase in the Physical driving force (VPD) and partially to a transient decrease in stomatal resistance resulting from reduced epidermal backpressure. In the second model, the transient decrease in stomatal resistance was attributed to a direct response of the guard cells to VPD. Both models based on water relations gave good fits of the data, emphasizing the need for further study regarding the metabolic nature of the guard cell response to humid

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01515.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A glycoprotein which occludes intercellular spaces in the inner cortex of legume nodules may be involved in controlling oxygen diffusion into rhizobial‐infected cells. Here we investigated this possibility by localizing the glycoprotein using monoclonal antibodies and immunogold labelling in nodulated roots of soybean cv. Clarke inoculated withBradyrhizobium japonicumstrain RCR3442 exposed to atmospheres with either 10, 21 (control) or 40% oxygen for 28d. Infected cells showed evidence of premature senescence when grown in above or below ambient pO2particularly at 10% oxygen, although cortical cells appeared to be little altered by oxygen treatment. In the inner cortical cells, more glycoprotein was seen to be occluding intercellular spaces of those nodules subjected to 40% oxygen and less in those nodules exposed to 10% oxygen, when compared to controls. This observation, made at the light microscope level (using silver enhancement) was confirmed under the TEM using immunogold labelling. Therefore, it is suggested that intercellular space glycoprotein is one of the structural components of the diffusion resistance in the cortex of legume nodule

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01516.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The origin, sequence and location of molecular damage arising during sub‐lethal drought is described in 4‐week‐old wheat (Triticum aestivumL.). Short episodes of water deprivation increased the uptake of iron within 6h of drought. Superoxide, precursor of the highly reactive hydroxyl radical in the presence of iron, was formed in the thylakoid membranes. Further draughting promoted destruction of chlorophylls (but not carotenoids), which was detectable after 14 h and preceded significant losses in relative water content. Peroxidation of lipids and a decreased protein content occurred after 26h of cumulative water deprivation but was confined to the shoots. In contrast, there was no significant loss of protein nor peroxidation of lipids in the root tissue, despite quantitatively larger, more rapid, losses in water content. These results indicate that damage arising in the early phases of drought appears to be initiated within the chloroplast and to be largely confined to the photosynthetic tissue. The pattern of drought‐induced damage in 11 other non‐xerophytes of the north temperate region was qualitatively similar to wheat, although the response to drought of the three cereals was more extreme than in the indigenous grasses and less extreme in ecologically stress‐tolerant species. A method for the simultaneous quantification of carotenoids in the presence of chlorophylls

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01517.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The mobility and deposition of silicon (Si) in cucumber plants grown in hydroponic culture were studied using scanning electron microscopy and energy dispersive X‐ray analysis under conditions of powdery mildew fungus infection. Following transfer to Si containing media, plants grown in the absence of Si showed rapid silicification of leafy tissue, primarily in the trichome bases. These plants also exhibited increased disease resistance toSphaerotheca fuliginea(Schlecht.:Fr.) Poll, and concentration of Si in the leaf epidermis surrounding the invading pathogen. Plants grown in Si‐supplemented media and transferred into Si‐deficient media contained residual Si in the leaf trichome bases, but failed to display disease resistance or silicification of host tissue surrounding the invading pat

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01518.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Light gradients were measured and correlated with chlorophyll concentration and anatomy of leaves in spinach (Spinacia oleraceaL.). Light gradients were measured at 450, 550 and 680 nm within thin (455 μm) and thick (630 μm) leaves of spinach grown under sun and shade conditions. The light gradients were relatively steep in both types of leaves and 90% of the light at 450 and 680 nm was absorbed by the initial 140 μm of the palisade. In general, blue light was depleted faster than red light which, in turn was depleted faster than green light. Light penetrated further into the thicker palisade of sun leaves in comparison to the shade leaves. The distance that blue light at 450 nm travelled before it became 90% depleted was 120 μm in sun leaves versus 76 μm in shade leaves. Red light at 680 nm and green light at 550 nm travelled further but the trends were similar to that measured at 450nm. The steeper light gradients within the palisade‐of shade leaves were caused by increased scattering of light within the intercellular air spaces and/or cells which were less compact than those in sun leaves. The decline in the amount of light within the leaf appeared to be balanced by a gradient in chlorophyll concentration measured in paradermal sections. Progressing from the adaxial epidermis, chlorophyll content increased through the palisade and then declined through the spongy mesophyll. Chlorophyll content was similar in the palisade of both sun and shade leaves. Chloroplast distribution within both sun and shade leaves was relatively uniform so that the chlorophyll gradient appeared to be caused by greater amounts of chlorophyll within chloroplasts located deeper within the leaf. These results indicate that the anatomy of the palisade may be of special importance for controlling the penetration of photo‐synthetically active radiation into the leaf. Changing the structural characteristics of individual palisade cells or their arrangement may be an adaptation that maximizes the absorption of light in leaves with varying mesophyll thickness due to different ambient light

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01519.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Light, probably acting through the photo‐receptor phytochrome, promotes germination of weed seeds when the soil is disturbed by tillage operations. A short period of burial is shown to induce an enormous ∼10000‐fold increase in light sensitivity in the seeds of the arable weedDatura feroxwhich is interpreted as a natural transition to the ‘very‐low‐fluence’ mode of phytochrome action. Field experiments indicated that germination of buried seeds may be triggered by millisecond‐exposures to sunlight and suggested a key role for the process of sensitization in the mechanisms whereby light requiring seeds detect the occurrence of soil cultivation events

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01520.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Stomatal responses to humidity were studied in several species using normal air and a helium: oxygen mixture (79:21 v/v, with CO2and water vapour added), which we termed ‘helox’. Since water vapour diffuses 2.33 times faster in helox than in air, it was possible to vary the water‐vapour concentration difference between the leaf and the air at the leaf surface independently of the transpiration rate and vice versa. The CO2concentration at the evaporating surfaces (ci), leaf temperature and photon flux density were kept constant throughout the experiments. The results of these experiments were consistent with a mechanism for Stomatal responses to humidity that is based on the rate of water loss from the leaf. Stomata apparently did not directly sense and respond to either the water vapour concentration at the leaf surface or the difference in water vapour concentration between the leaf interior and the leaf surface. In addition, stomatal responses that caused reductions in transpiration rate at low humidities were accompanied by decreases in photosynthesis at constantci, suggesting heterogeneous (patchy) stomatal cl

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01521.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Studies of the isoprene emission rate in response to changes in photon‐flux density and CO2partial pressure were conducted using a recently developed on‐line isoprene analyser combined with a gas exchange system and chlorophyll fluorometer. Upon darkening, the isoprene emission rate from leaves of aspen (Populus tremuloidesMichaux.) began to decline immediately, demonstrating that the internal pool of isoprene, or its precursors, is small and that the instantaneous emission rate is tightly coupled to the rate of synthesis. A post‐illumination burst of isoprene was observed within 5 min after darkening and lasted for 15–20 min in four isoprene‐emitting species that were examined. In leaves of eucalyptus (Eucalyptus globulusLabill.), the magnitude of the post‐illumination burst was dependent on the photon‐flux density that existed before darkening, but not on ambient CO2partial pressure. The dependence of the post‐illumination burst on photon‐flux density paralleled that for the steady‐state rate of isoprene emission. A step‐wise increase in intercellular CO2partial pressure from 24.5 to 60 Pa resulted in an immediate decrease in isoprene emission rate and non‐photochemical fluorescence quenching, but an increase in CO2assimilation rate. Given the several recent studies that link isoprene emission to chloroplastic processes, the results of this study indicate that the linkage is not dependent on the rate of CO2flux through the reductive pentose phosphate pathway, but rather on more complex relationships involving metabolites not appreciably influenced

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01522.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Intracellular and extracellular free calcium was measured in cortical cells from apple fruit (Malusdomestica Borkh cv. Cox's Orange Pippin) using calcium‐selective microelectrodes. It was difficult to position microelectrodes in the cytoplasm, and thus most intracellular measurements reflected vacuolar concentrations of about 0.6mol m−3free calcium. Extracellular free calcium was measured in wells (0.2mm3) that had been cut through the epidermis of the fruit, then filled with osmoticum. Concentrations of free calcium in the sampling well varied between 0.02 and 1.3 mol m−3, and were related to the calcium content of the tissue. Functioning of the plasma membrane, and perhaps the supply of calcium for intracellular needs during fruit ripening and storage, may require mol m−3concentrations of extracellular free calcium. Thus, it is suggested that low levels of extracellular free calcium in calcium‐deficient fruit may be partly responsible for development of deficiency

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01523.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY