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51.
Almond plants (Amygdalus communis L.) of the Garrigues variety were grown in the field drip irrigated and rainfed. Leaf water potential (Ψ) and leaf conductance
(g1) were determined throughout one growing season. Pre-dawn measurement for Ψ in the irrigated treatment was consistent through
the growing season, whereas in the rainfed treatment it decreased gradually. Ψ values at midday (Ψ minimum) was closely dependent
on atmospheric evaporative demand, and their recovery was quicker in the wet treatment than in the dry. The g1 values were higher in the wet than dry treatments, decreasing in both cases by leaf ageing. Maximum values for g1 were reached when evaporative demand was highest in the day. The relationship between Ψ and g1 revealed a decrease in the hysteresis throughout the growing season, being most marked in the dry treatment. The results
highlight the close dependence of Ψ and g1 on evaporative demand, leaf ageing and irrigtion treatment during the growing season. 相似文献
52.
Almond plants (Amygdalus communis L. cv. Garrigues) were grown in the field under drip irrigated and non irrigated conditions. Leaf water potential () and leaf conductance (g1) were determined at three different times of the growing season (spring, summer and autumn). The relationships between and g1 in both treatments showed a continuous decrease of g1 as decreased in spring and summer. Data from the autumn presented a threshold value of (approx. –2.7 MPa in dry treatment, and approx. –1.4 MPa in wet treatment) below which leaf conductance remained constant. 相似文献
53.
Summary For patch-clamp measurements cultured kidney (OK) cells were exposed to osmotic and mechanical stress. Superfusion of a cell in whole cell configuration with hypotonic media (190 mOsm) evokes strong depolarization, which is reversible by returning to the isotonic bath medium. In the cell-attached configuration the exposure to hypotonic media evokes up to six ion channels of homogeneous single-channel properties in the membrane patch. Subsequently, the channels became activated after a time lag of a few seconds. At an applied membrane potential of 0 mV, the corresponding membrane current is directed inward and shows a transient behavior in the time range of minutes. In the same membrane patch these ion channels can be activated by application of negative hydrostatic pressure. The channel has a single-channel conductance of about 22 pS and is permeable to Na+ and K+ as well as to Cl–. It is suggested that volume regulation involves mechanoreceptor-operated ion channels. 相似文献
54.
Stomatal sensing of the environment 总被引:1,自引:0,他引:1
C. M. WILLMER 《Biological journal of the Linnean Society. Linnean Society of London》1988,34(3):205-217
The effects of environmental factors on stomatal behaviour are reviewed and the questions of whether photosynthesis and transpiration eontrol stomata or whether stomata themselves control the rates of these processes is addressed. Light affects stomata directly and indirectly. Light can act directly as an energy source resulting in ATP formation within guard cells via photophosphorylation, or as a stimulus as in the case of the blue light effects which cause guard cell H+ extrusion. Light also acts indirectly on stomata by affecting photosynthesis which influences the intercellular leaf CO2 concentration ( C i ). Carbon dioxide concentrations in contact with the plasma membrane of the guard cell or within the guard cell acts directly on cell processes responsible for stomatal movements. The mechanism by which CO2 exerts its effect is not fully understood but, at least in part, it is concerned with changing the properties of guard cell plasma membranes which influence ion transport processes. The C i may remain fairly constant for much of the day for many species which is the result of parallel responses of stomata and photosynthesis to light. Leaf water potential also influences stomatal behaviour. Since leaf water potential is a resultant of water uptake and storage by the plant and transpirational water loss, any factor which affects these processes, such as soil water availability, temperature, atmospheric humidity and air movement, may indirectly affect stomata. Some of these factors, such as temperature and possibly humidity, may affect stomata directly. These direct and indirect effects of environmental factors interact to give a net opening response upon which is superimposed a direct effect of stomatal circadian rhythmic activity. 相似文献
55.
The kinetic parameters of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (EC 4.1.1.39) in wheat (Triticum aestivum L.) and rice (Oryza sativa L.) were determined by rapidly assaying the leaf extracts. The respective K
m and V
max values for carboxylase and oxygenase activities were significantly higher for wheat than for rice. In particular, the differences in the V
max values between the two species were greater. When the net activity of CO2 exchange was calculated at the physiological CO2-O2 concentration from these kinetic parameters, it was 22% greater in wheat than in rice. This difference in the in-vitro RuBP-carboxylase/oxygenase activity between the two species reflected a difference in the CO2-assimilation rate per unit of RuBP-carboxylase protein. However, there was no apparent difference in the CO2-assimilation rate for a given leaf-nitrogen content between the two species. When the RuBP-carboxylase/oxygenase activity was estimated at the intercellular CO2 pressure from the enzyme content and kinetic parameters, these estimated enzyme activities in wheat and rice were similar to each other for the same rate of CO2 assimilation. These results indicate that the difference in the kinetic parameters of RuBP carboxylase between the two species was offset by the differences in RuBP-carboxylase content and conductance for a given leaf-nitrogen content.Abbreviations DTT
dithiothreitol
- EDTA
ethylenediamine-tetraacetic
- PAR
photosynthetically active radiation
- RuBP
ribulose-1,5-bisphosphate 相似文献
56.
The red light-stimulated component of unrolling in sections from 7-d-old dark-grown barley (Hordeum vulgare L.) leaves is inhibited by ethyleneglycol-bis-(-aminoethyl ether)-N,N,N,N-tetracetic acid (EGTA). A free-Ca2+ activity of less than 40 M restores the ability to respond to red light, but only if supplied within 1 h of red light. Magnesium ions are an ineffective substitute. At least two processes in unrolling appear to be Ca2+-sensitive.Fluence-response measurements indicate that the levels of the far-red-absorbing from of phytochrome (Pfr) still present 4 h after red-light treatment should be above saturation for the unrolling response; consequently, loss of Pfr does not explain the loss in effectiveness of Ca2+ during prolonged EGTA treatment. However, if a further red-light treatment is given simultaneously with Ca2+ addition 4 h after the initial light stimulus, then full unrolling occurs in EGTA-treated sections. These data indicate that, under normal circumstances, a functional change in the properties of Pfr must occur, uncoupling it from the transduction chain.Abbreviations EGTA
ethyleneglycol-bis-(-aminoethylether)-N,N,N,N,-tetracetic acid
- FR
far-red light
- Mes
2-(N-morpholino)ethanesulphonic, acid
- Pfr
far-red absorbing form of phytochrome
- Pr
red-absorbing form of phytochrome
- R
red light 相似文献
57.
The aim of this work was to examine the effect of abrupt changes in temperature in the range 5 to 30°C upon the rate of photosynthetic carbon assimilation in leaves of barley (Hordeum vulgare L.). Measurement of the CO2-assimilation rate in relation to the intercellular partial pressure of CO2 at different temperatures and O2 concentrations and at saturating irradiance showed that as the temperature was decreased photosynthesis was saturated at progressively lower CO2 partial pressures and that the transition between the CO2-limited and ribulose-1,5-bisphosphate-regeneration-limited rate became more abrupt. Feeding of orthophosphate to leaves resulted in an increased rate of CO2 assimilation at lower temperatures at around ambient or higher CO2 partial pressures both in 20% O2 and in 2% O2 and it removed the abruptness in the transition between the CO2-limited and ribulose-1,5-bisphosphate-regeneration-limited rates. Phosphate feeding tended to inhibit carbon assimilation at higher temperatures. The response of carbon assimilation to temperature was altered by feeding orthophosphate, by changing the concentrations of CO2 or of O2 or by leaving plants in the dark at 4°C for several hours. Similarly, the response of carbon assimilation to phosphate feeding or to changes in 2% O2 was altered by leaving the plants in the dark at 4°C. The mechanism of limitation of photosynthesis by an abrupt lowering of temperature is discussed in the light of the results.Abbreviations A
rate of CO2 assimilation
-
P
i
intercellular partial pressure of CO2
- RuBP
ribulose-1,5-bisphosphate 相似文献
58.
Markus Riederer Kathrin Kurbasik Rainer Steinbrecher Andreas Voss 《Trees - Structure and Function》1988,2(3):165-172
Summary A method for the rapid determination of the lengths and surface areas of very large samples of needles of Picea abies (L.) Karst. using a computer-aided image analysis system was developed. Two independent methods for measuring non-destructively the volumes of individual needles and of all needles attached to a twig were devised. The surface areas and lengths of about 38000 needles sampled from the three youngest needle age-classes (1986, 1985, 1984) of 48 trees approximately 130 years old at four sites in the Fichtelgebirge mountains (N. E. Bavaria, FRG) were measured. The frequency distributions of lengths and areas for each site and age-class are given. Variability of needle size was fairly large. Even though the sites differed in climate, soil, and air pollution levels no consistent effect of these factors on needle size could be detected. Needle lengths and surface areas did not correlate with either the total chlorophyll content of the needles or the degree of crown thinning. The needle surface area (in mm2) of fully developed P. abies needles can be estimated by the empirical equation surface area = 4.440 x needle length -24.8 (r = 0.937), and the needle volume (in mm3) by needle volume = 0.208 x projected needle area
1.353 (r = 0.969). 相似文献
59.
60.
The growth of barley (Hordeum vulgare L.) leaves is reduced by salinity. We used the Instron extensometric technique to measure the reversible and irreversible compliance of the expanding regions of growing barley leaves from plants exposed to 1, 40, 80 and 120 mM NaCl in nutrient solution. Two barley cultivars differing in salinity resistance (cv ‘Arivat’ and cv ‘Briggs’) were compared over 5d of leaf growth. During the period of most active leaf expansion, salinity reduced reversible compliance and increased compliance in the leaf segments, although responses to salinity were complex and changed over the course of leaf expansion. Salinity increased irreversible compliance more in the salt-sensitive cultivar Arivat than in the more salt-tolerant cultivar Briggs. Elemental analysis of the basal leaf segments used for extensometry revealed an accumulation of Na and a depletion of Ca in segments from salinized plants, resulting in very high Na: Ca ratios in salinized expanding tissue. The concentrations of K and Mg in basal leaf tissue were elevated by salinity. Our data do support the hypothesis that the inhibition of leaf expansion by salinity stress is mediated by a decline in irreversible extensibility. We suggest that reduced Ca availability in expanding leaf tissue may contribute to growth reduction in salt-stressed barley seedlings. 相似文献