摘要:

Abstract.A model of water flow from the soil into the plant, and from the plant to the atmosphere is described. There are three state variables in the model: the soil, root and shoot water contents. The flow rate of water from the soil to the root is calculated by dividing the gradient in water potential by a resistance, comprising the resistance from the bulk soil to the root surface, and that from the root surface to the root interior. The resistance in the soil depends on the soil hydraulic conductivity, which in turn depends on the soil water potential. The flow rate from the root to the shoot is given by the gradient in water potential divided by a resistance, which depends on the structural dry mass of the plant. Transpiration is described by the Penman‐Monteith equation. The plant water characteristics can be modified to take account of osmotic and cell wall rigidity parameters. The model incorporates the concept of shoot/root ‘messages’ of water stress, which influence stomatal conductance. The message works through the generation of a hormone as the pressure potential in the shoot (mesophyll) or root falls. This hormone induces a shift of osmoticum from the guard cells to the surrounding mesophyll cells, which causes an increase (i.e. closer to zero) in the osmotic potential in these cells. This, in turn, causes a decrease in their pressure potential, and so reduces stomatal conductance. The model is used as a framework to address some of the issues that have recently been raised concerning the role of water potential in describing water flow through plants. We conclude that, with the hormone present, there is unlikely to be a unique relationship between stomatal conductance and shoot total water potential, since stomatal conductance depends on the pressure potential in the guard cells, which may differ from that in other cells. Nevertheless, this does not imply that water potential is not an important, and indeed fundamental, component for describing water flow through plants. Other aspects of water flow through plants are also considered, such as diurnal patterns of shoot, root and soil water potential components. It is seen that these may differ from the commonly held view that, as the soil dries down, they all attain the same values during the dark period, and which, as we show, is largely unsubstantiated either theoretically or experimen

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01524.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Epidermal (non‐stomatally‐controlled) conductance from the fourth leaf, first node leaf, flag leaf and ear of durum wheat (Triticum turgidumvardurumL.) grown under Mediterranean field conditions has been measured, along with leaf stomatal frequency and the amount and distribution of epicuticular waxes. Measurements were carried out on varieties and land‐races from the Middle East, North Africa, ‘Institut National de la Recherche Agricole’ (INRA) and ‘Centra Internacional de Mejora de Maiz y Trigo’ (CIMMYT). Significant differences were observed among genotypes in the epidermal conductances (ge) of the four organs. For each of the four organs tested, genotypes from the Middle East and CIMMYT showed higher ge. values than those from North Africa and INRA. Ears showed epidermal conductances that were more than four times higher than those of leaves when ge. values were expressed per unit dry weight. The amount of epicuticular waxes was higher in the fourth leaves, intermediate in the first node and flag leaves and lower in the ears. For each organ, gedifferences among genotypes were unrelated with the amount of epicuticular waxes. Removal of epicuticular waxes by dipping the organs into chloroform significantly increased the epidermal conductance for the fourth and first node leaves and the ear. However, this did not occur for the flag leaf. For the fourth leaf, geof intact leaves and geof leaves in which epicuticular waxes were removed were unrelated (r = ‐0.265). The regression coefficient of this relation for the first node and flag leaves showed values of 0.666 and 0.650 (P>0.05), respectively, and values were even higher in the ear (r>m 0.892,P>0.01). Scanning electron microscope analysis showed that wax bloom decreased from the fourth leaf to the flag leaf, whereas the extent of amorphous wax increased. Wax bloom in leaves consisted mainly of deposits of thin wax plates. In the ears and the adaxial surface of flag leaves, fibrillar waxes predominated. In the first node and flag leaves, the wax deposits on the adaxial side cover the surface of the leaf more densely and uniformly than those on the abaxial side. There was no significant correlation between geand total stomatal density, or between geand either adaxial or abaxial stomatal density for any sample of the three different leaves. The contribution of epicuticular waxes plus total stomatal frequency only explained 42.4, 11.8, 28.3 and 16% of ge(per unit leaf area) variations for the fourth leaf, first node leaf, flag leaf and the combined variation of the three leaves together, respectively. From these results, it is concluded that complex interrelationship between different morphophysiological characteristics probably control gedifferences among genotypes and that these interrelationships differ for each diffe

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01525.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Profiles of self‐generated ion currents associated with the growing primary root tips of intactHordeum vulgareL. andTrifolium repensL. (nonnodulated) seedlings were measured using a highly sensitive vibrating electrode in media containing NH+4or NO‐3, and compared to control roots growing in nitrogen free media. Under these three nutrient regimes, positive current entered the root at regions corresponding to the meristematic tissues and main elongation zones of root tips and left from the mature root tissues. Mapping the surface of the roots with a pH‐sensitive microelectrode revealed regions of external alkalinity where positive electrical current entered the root, and external acidity where positive current exited. The correlation between pH‐profile and the pattern of ion current generation in these experiments suggests that H+ions were responsible for carrying the bulk of the root‐generated current. Assimilation of NHJ results in net H+extrusion while assimilation of NO‐3, results in net OH‐3efflux. Growth on NH+4, as compared to growth on NO‐3, stimulated the magnitude of the electrical current but did not affect significantly the growth rate of the roots. However, despite the differing stresses on internal pH regulation that arise due to growth on the two exogenous forms of combined nitrogen, the current profiles were qualitatively similar under the different conditions that were examined. The role of the circulating proton current is not yet known; however, the constancy of the current profile under different nutrient regimes sustains the hypothesis that the current may have a role in the regulation o

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01526.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The potential for thermal acclimation of photosynthetic electron transport by guard cell chloropiasts (GC ch) was assessed in epidermal peels taken from the abaxial side ofSaxifraga cernualeaves grown at 20°C and 10°C. Chlorophyllafluorescence induction kinetics measured in pairs of guard cells in individual stomata from tissue grown at 10 °C demonstrated a rise in the fluorescence to a maximum and a larger amplitude in variable fluorescence when measured at temperatures below 18°C than was seen in GC ch from tissue grown at 20°C. The rates of fluorescence quenching in 10°C‐grown tissue were also faster than in 20°C‐grown tissue when measured at temperatures below 18°C. State 1‐State 2 transitions by GC ch were measured at selected temperatures between 5 and 25 °C as changes in the magnitude of the fluorescence emission maxima at 685, 695 and 730nm (F685, F695 and F730) measured at 77K. At measuring temperatures of 5 and 10°C, GC ch in tissue grown at 10 °C showed a greater transition to State 2 (a larger F730/F695 ratio) than did GC ch in tissue grown at 20 °C. At measuring temperatures of 20 and 25 °C, there was no difference in either the kinetics or the magnitude of the State 1 to State 2 transition in the two tissues. The ultrastructure of GC ch from tissues grown at 10 and 20 °C was also examined using transmission electron microscopy. Less than half (48%) of the grana from the higher temperature grown tissue had more than nine thylakoids/grana. Grana in GC ch which had developed at 10 °C showed a dramatic reduction in stacking, such that 85% of the grana contained no more than two thylakoids. The reduction in grana stacking was also accompanied by a decrease in the degree of appression of thylakoid membranes. The results demonstrate a capacity for thermal acclimation of GC ch function to low temperatures. This acclimation is associated with alterations in the chloro

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01527.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The effects were studied of season‐long (75 and 88d) exposure of rice (Oryza sativaL. cv. IR‐30) to a range of atmospheric CO2concentrations in outdoor, computer‐controlled, environment chambers under natural solar radiation. The CO2concentrations were maintained at 160, 250, 330, 500, 660 and 900μmol mol‐1air. Photosynthesis increased with increasing growth CO2concentrations up to 500u.mol moP1, but levelled off at higher CO2values. Specific leaf area also increased significantly with increasing CO2. Although leaf dry weight and leaf area index increased, the overall response was not statistically significant. Leaf nitrogen content dropped slightly with elevated CO2, but the response was not statistically significant. The specific activity of ribulose bisphosphate carboxylase/oxygenase (rubisco) declined significantly over the CO2concentration range 160 to 900μmol mol‐1. When expressed on a leaf area basis, rubisco activity decreased by 66%. This was accompanied by a 32% decrease in the amount of rubisco protein as a fraction of the total soluble leaf protein, and by 60% on a leaf area basis. For leaves in the dark, the total rubisco activity (CO2/Mg2+‐activated) was reduced by more than 60%. This indicates that rice accumulated an inhibitor in the dark, probably 2‐car‐boxyarabinitol 1‐phosphate (CA‐1‐P). However, the inhibitor did not seem to be involved in the acclimation response. The degree of carbamylation of the rubisco enzyme was unchanged by the CO2 growth regime, except at 900 [μmol mol‐1where it was reduced by 24%. The acclimation of rice to different atmospheric CO2conditions involved the modulation of both the activity and amount of r

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01528.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.This paper describes a simple method to estimate the root water potential of trees using the root suckers as xylemic probes. On the day before the water potentials were measured in pressure chamber, all the sucker shoots were enclosed in plastic bags to prevent transpiration. Under the premise that the potential at two points in a flow system would be equal if there were no flux between these points, the sucker shoot water potential estimates the root water potential. The results are not dependent on the sucker architecture, are consistent with the soil‐plant‐atmosphere continuum concept, and are supported by psychrometric measureme

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01529.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In this study, computer modelling has been used to simulate and analyse the effects which non‐homogeneous stomatal conductance (patchiness) might have on the appearance of the macroscopic relationship between photosynthetic CO2assimilation (A) and intercellular CO2(Q) in leaves. The problem was formalized using the assumptions that (1) the biochemical model of Farquhar, von Caemmerer&Berry applies [Planta,149, 78–90 (1980)]; (2) that the parameters for the model are fixed for the period required to determine the relationship; (3) that the distribution of conductances in any leaf area is normal (but restricted to positive values); and (4) that the leaf is perfectly heterobaric. The model is interactive, allowing the user to explore–well beyond the conditions for which data are presented here–the effects of carboxylation capacity, photosynthetic electron transport rate and photorespiration over a range of possible conductances and degrees of patchiness. Regardless of the parameters used in the model, the results fail to predict the change in appearance of theA‐C1curve which has been attributed to patchiness in other reports: even when conductance varies with a standard deviation of twice its mean value, the effects on the curve are minor. The need for reconsideration of the methods currently used to interpret gas exchange studies is

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01530.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The xanthophyll content of wild type and abscisic acid (ABA) ‐ deficient mutants of pea andArabidopsis thalianawas determined. Thewiltymutant of pea was indistinguishable from the non‐mutant control. In contrast, plants homozygous for mutant alleles at theabalocus ofArabidopsiswere very different from wild type. In these mutants, zeaxanthin accumulated to abnormally high levels. The major carotenoids, violaxanthin and 9′‐cis‐neoxanthin were virually absent from the mutant chromatograms. It was concluded that theabagenetic lesion impairs the epoxidation of zeaxanthin to violaxanthin and that this results in an inability to accumulate ABA. This provides clear evidence that zeaxanthin is a precurs

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01531.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The potential role of stomatal closure in the control of xylem embolism is investigated by means of a simple model of hydraulic flow in plants. Maintenance of a maximally efficient conducting system requires the stomata to close in an appropriate fashion as evaporative demand increases in order to prevent shoot water potentials falling below the threshold value at which cavitations occur. The model showed that the optimal stomatal behaviour required depends on soil water availability. Further analysis of the model demonstrated that there could be certain circumstances where loss of a proportion of the conducting tissue by embolisms can, perhaps surprisingly, be beneficial in terms of maximizing stomatal aperture and hence short‐term productivity. The results are discussed in relation to the signals controlling stomatal aperture, and it is shown that (1) optimal control cannot be obtained using information on leaf water potential alone, and (2) information relating to soil water potential is a necessary requirement for optimal contro

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01532.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In callus cultures ofNicotiana plumbaginifolia, the activity of glutamate dehydrogenase was repressed by glucose, whereas, on the contrary, carbon and energy source deprivation induced a remarkable increase in specific activity. Definition of these two opposite types of response was made possible by the use of glycerol as a non‐repressing carbon source: in this condition, glutamate dehydrogenase activity reached an intermediate level, which was similar to the derepressed values of activity obtainable when cultures were allowed to exhaust the glucose supply in the medium. Isoelectric focusing analysis revealed the existence of three different isoenzymatic patterns which could be correlated to the three different levels of specific activity: repressed (glucose), induced (carbon starvation) and intermediate (glycerol). Repression affected mainly the four more cathodic bands which were predominant in non‐repressed conditions. The possible catabolic role of these isoenzymes is discus

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01533.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY