摘要:

Abstract.A dynamic model of whole leaf C3photosynthesis is constructed using a modified version of the Farquliar‐von Caemmerer approach. The model is designed to provide a physiological basis to understand observations of assimilation in environments with varying photon flux densities, including induction phenomena. The model couples the effect of light activation and dark deactivation of enzymes, stomatal conductance responses, and variations in the pools of carbon cycle intermediates. The dynamic components are viewed on three time scales, the slowest of which (min to h) involves changes in stomatal conductance and the activation stale of Rubisco. On a time scale of seconds to a few minutes, adjustments in pools of biochemical components of the photosynthetic pathway occurs. The most rapid time scale corresponds to the equilibration time of intercelluar CO2concentration through gaseous diffusion and is here assumed to occur instantaneously. The model form includes a single pool for reduced intermediates including RuBP, a single pool for components of the glycolate pathway, and a third component corresponding to the activation state of Rubisco. This is coupled to a previously described model for the dynamics of stomatal conductance, giving a final model form consisting of six non‐linear ordinary differential equations, of which three control conductance dynamics and three control assimilation. The coupling between these occurs through the variable pi, the intercellular partial pressure of CO2.Only three of the parameters for the assimilation portion of the model require dynamic data to estimate. The remaining parameters are estimated from steady‐state data. The model is calibrated using previously collected data on the tropical understory plantAlocasia macrorrhizaand is shown to have qualitatively similar behaviour to that of experimental measurements using simple changes in PFD, as well as a complex sequence of such ch

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00957.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A model of photosynthesis (PGEN) is presented. The model assumes that optimal use is made of the leaf nitrogen available for partitioning between the carboxylase and thylakoid components. This results in predictions of Rubisco and chlorophyll concentrations very similar to those measured elsewhere. A function is incorporated which represents the detrimental effects of negative leaf water potentials on the Calvin cycle, producing a quantitative and mechanistic trade‐off between CO2 entering, and H2O leaving, the leaf. Thus, an optimal stomatal conductance and associated internal partial pressure of CO2exists for any given set of environmental conditions. The model calculates this optimal state for the leaf, which is its output. The model was subjected to changes in the following parameters: soil water potential, irradiance, ambient CO2 partial pressure, leaf temperature, leaf‐to‐air vapour pressure deficit, wind speed, atmospheric pressure, leaf nitrogen content, root dry weight and leaf width. These perturbations resulted in changes in predicted optimal conductance which were very similar to what has been observed. In general, as the capacity of the leaf to fix CO2increased, so did the predicted optimal conductance, with the internal partial pressure of CO2 being maintained close to

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00958.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Local exocytosis with concomitant deposition of cell wall material (plugs) was induced in mature characean internodal cells by application of Sephadex beads loaded with a chlortetracycline (CTC)/CaCl2solution. Plugs can be formed anywhere on the cells independently of structural and/or functional plasma membrane domains, provided that the pH of the CTC/CaCl2solution is above 5.5. Plug formation is inhibited by cytochalasin B and membrane depolarizing agents. Treatment with fusicoccin enhances exocytosis. The results suggest that actin filaments are involved in the transport of vesicles and endoplasmic reticulum cisternae towards the cell membrane, and that the membrane potential determines the extent of CTC mediated Ca2+influx.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00959.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Wphen there is no external source of water, plants can grow by mobilizing internal water from nongrowing tissues. We investigated how this internal water moves by measuring continuously and simultaneously the water potential (ψw) of soybean (Glycine maxL. Merr.) seedlings in the upper, growing stem tissues and the lower, non‐growing stem tissues. When external water was available to the roots, the stems grew rapidly and the ψwof the growing tissue was continually below that of the nongrowing tissue and the medium around the roots. This indicated that a growth‐induced gradient in ψwfavoured water movement from the external source to the growing cells. When the external source was removed, the ψwof the growing tissue remained constant for a time and the ψwof the nongrowing tissue decreased somewhat. Growth took place slowly as water was withdrawn from the nongrowing tissue but ψwgradients continued to favour water transport to the growing cells. On the other hand, if this internal source was removed by excision, growth ceased abruptly. In this case, the cell walls relaxed and the ψwof the growing tissue decreased by about 0.1 MPa instead of remaining constant. The ψwof the detached nongrowing tissues remained constant instead of decreasing. This indicates not only that water mobilization required attached nongrowing or slowly growing tissues but also that mobilization affected wall relaxation. Thus, ψwdifferences may mobilize internal water, may explain the continued growth of plants and plant parts removed from external sources of water, and may account for discrepancies in measurements of cell wall properties in gro

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00960.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Water uptake is required when plants enlarge but growth may also occur when no external water is present. To determine whether this growth also depends on water, we studied etiolated seedlings of soybean (Glycine maxL. Merr.) deprived of external water by transplanting to vermiculite of low water content or by transferring to water‐saturated air. When the external water supply was decreased or removed, the roots continued to grow rapidly but the stems abruptly decreased in growth (in 1 min) and continued to grow slowly. The stem tissues gained water content in the upper elongating region and lost water content in the basal region. Removal of the basal stem caused growth to slow further. When all tissues surrounding the stem elongating region were removed simultaneously, stem growth decreased abruptly to near zero. Control experiments showed that the decreased growth was not caused by wounding or the removal of the auxin or nutrient supply. It is concluded that growth always depended on a source of water and, when external supplies were absent, internal water was mobilized to enlarging tissues of shoots and roots mostly from the basal stem tissues in these seedling

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00961.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The objective of this study was to determine how mycorrhizal infection of one generation of plants influences the nutrient dynamics of seeds and seedlings comprising the subsequent generation. We showed that, forAvena fatuaL., seeds produced by mycorrhizal (M) plants consistently contained significantly more phosphorus (particularly the phytate P and residual P fractions) than seeds produced by non‐mycorrhizal (NM) plants. We also followed the development of spikelets produced by M and NM plants. The rates of increase in spikelet dry weight and nitrogen content were largely unaffected by mycorrhizal infection. However, the rate of P accumulation into spikelets was significantly increased by mycorrhizal infection. Greater endosperm P reserves in seeds produced by M plants were associated with greater rates of P accumulation in resultant seedlings. Moreover, offspring plants (all NM) produced by M mother plants had significantly higher root and rhizosphere phosphatase, ATPase and phytase activities than offspring plants produced by NM mother plants. This persistent maternal effect has never before been described. Our results suggest that mycorrhizal infection of one generation of plants may have substantial positive effects on the offspring generation, and thus, may influence plant population dynamic

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00962.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The effect of water‐stress on photosynthetic carbon metabolism in spinach (Spinacia oleraceaL.) has been studied in experiments in which water‐stress was induced rapidly by floating leaf discs on sorbitol solutions or wilting detached leaves, and in experiments in which water‐stress was allowed to develop gradually in whole plants as the soil dried out. In both short‐ and long‐term water stress, the rate of photosynthesis in saturating CO2did not decrease until leaf water potential decreased below ‐1.0 MPa. However, at smaller water deficits there was already an inhibition of starch synthesis, while sucrose synthesis remained constant or increased. This change in partitioning was accompanied by an increase in activation of sucrose‐phosphate synthase (revealed as an increase in activity assayed in the presence of low hexose‐phosphate and inorganic phosphate, while the activity assayed with saturating hexosephosphates remained unaltered). Water‐stressed leaves had a two‐ to three‐fold higher sucrose content at the end of the night, and contained less starch than non‐stressed leaves. When leaves were held in the dark, sucrose was mobilized initially, while starch was not mobilized until the sucrose had decreased to a low level; in water‐stressed leaves, starch mobilization commenced at a two‐fold higher sucrose content. It is concluded that water‐stressed leaves maintain higher sucrose and lower starch levels than non‐stressed leaves. This response is found in rapid and long‐term stress, and represents an in

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00963.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The effect of growth temperatures on quantum yield (φ) was examined for leaves at different stages of development within the immature canopies of two crops of field grown maize (Zea mayscv. LG11) sown on 3 May and 20 June 1990. During the period of 23 to 49d after sowing, the crop sown on the 3 May experienced temperatures below 10°C on 19 occasions compared with only two for the crop sown on 20 June. A period of severe chilling at the end of May and the beginning of June was associated with a marked reduction in φ for all leaves in the early‐sown crop. This chill‐induced depression in φ was greater in recently emerged than more mature leaves in the canopy and was found to be accompanied by modifications in the polypeptide profiles of thylakoids isolated from the leaves. During the chilling period, decreases in some polypeptides, notably in the range of 41–42 and 20kDa apparent molecular size, and increases of polypeptides of c. 15–16kDa were observed compared with leaves developing at warmer temperatures in July. The efficiency of converting intercepted radiation into dry matter (conversion efficiency) was 42% lower in the early‐ than late‐sown crop, but no significant relationship between conversion efficiency and quantum yield was found in e

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00964.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Because CO2diffuses 10000 times more slowly through water than air, there may be strong selective pressure for increased water repellency in terrestrial plant leaves. In the present study, leaf trichomes appeared to have a strong influence on leaf water repellency (i.e. degree of water droplet formation on the leaf surface) as well as the retention of droplets on the leaf. Based upon evaluation of 38 plant species from 21 families, we found that leaves with trichomes were more water repellent, especially where trichome density was greater than 25mm2. However, droplet repellency and retention were both high in some species where trichomes entrapped droplets. Finally, the lensing effects of water droplets on leaf surfaces increased incident sunlight by over 20‐fold directly beneath individual droplets. These results may have important implications for such processes as stomatal function, whole leaf photosynthesis, and transpiration for a large variety of plant specie

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00965.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Sunflower plants (Helianthus annuusL., cv. CGL 208) were field‐grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen. Nutrient‐stress (N‐stress) plants received control levels of irrigation but no nutrient amendments and were determined to be nitrogen‐limited. Water‐stress (H2O‐stress) plants received control levels of fertilizer nitrogen, but no irrigation after approximately 6 weeks of plant growth. Both stress treatments reduced maximum and diurnal net photosynthesis (A) but resulted in different physiological or biochemical adjustments that tended to maintain or increase A per unit of resource (nitrogen or water) in shortest supply while decreasing the ratio of A per unit of abundant resource. Nutrient‐stress reduced total foliar nitrogen, foliar chlorophyll, and initial and total RuBPCase activities, thereby enhancing or preserving photosynthetic nitrogen‐use efficiency (NUE), defined as the maximum A observed per unit of leaf nitrogen, relative to the control and H2O‐stress treatments. In addition, N‐stress reduced photosynthetic water‐use efficiency (WUE), defined as the ratio of A to stomatal conductance to water vapour (g). The slope of A versus g increased with H2O‐stress. In addition, sunflower plants responded to H2O‐stress by accumulating foliar glucose and sucrose and by exhibiting diurnal leaf wilting, which presumably provided additional improvements in photosynthetic WUE through osmoregulation and reduction of midday radiation interception respectively. Photosynthetic NUE was decreased by H2O‐stress in that control levels of total nitrogen, foliar chlorophyll, and RuBPCase activities were maintained even after mean diurnal levels of A had fallen to less than 50% of the control level. We conclude that field‐grown sunflower manages a trade‐off between photosynthetic WUE and NUE, increasing use efficiency of the scarce resource while decreasing use ef

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00966.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY