摘要:

Abstract.Important physiological processes, photosynthesis, respiration, carbon allocation and stomatal function are known to be affected by air pollutants. A wide range in sensitivity of photosynthesis both within and between species is evident from the literature for the pollutants sulphur dioxide, ozone, nitrogen oxide and hydrogen fluoride. Some of this variation is clearly due to genetic factors, but much is in response to differences in environmental conditions both prior to and during fumigation. Exposure of plants to mixtures of pollutants generally reduced the threshold at which effects were first detected and increased the level of inhibitory responses. In the majority of studies on stomatal responses to air pollutants, opening occurs at low concentrations, below the threshold for effects on photosynthesis, and closure occurs at injurious concentrations; this latter response often following the inhibition of photosynthesis. Effects on carbon allocation have been reported in response to air pollutants. Changes usually favour leaf development over root growth, which can compensate for a decline in net assimilation rate up to a certain point but may limit water uptake from soils with low moisture content. Future research into physiological effects of air pollutants should incorporate an integrated approach in which both key physiological parameters and growth parameters are measured together with estimates of the effective dose of pollutant. In this way, the underlying mechanisms to changes in growth and development will be more fully understood.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01913.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.In addition to photosynthesis as in the leaf, fruit possess a system which refixes CO2from the mitochondrial respiration of predominantly imported carbon. This pathway produces malate by the action of phosphoenolpyruvate carboxylase, PEPC, (E.C. 4.1.1.31) and appears to be regulated primarily by the cytosolic concentration of HCO3/CO2and malate. Malate is stored in the vacuole as malic acid, constituting a major carbon pool and a potential substrate for respiration. The PEPC in apple fruit proves to be an efficient form of the enzyme with low Michaelis constants, i.e. Km = 0.09 mol m‐3PEP and 0.2 mol m–3HCO3, and large Ki= 110 mol m‐3HCO3. In fleshy fruit, chlorophyll and chloroplasts are unevenly distributed; they resemble the C3sun‐type and arc concentrated in the perivascular tissue, with smaller chloroplasts, fewer grana per chloroplast and a larger degree of vacuolation than commonly found in a leaf of the same species. Fruit photosynthesis often compensates for respiratory CO2loss in the light. However, due to respiration in the dark, CO2loss is in excess of photosynthetic gain in the light, such that a continual loss of CO2was observed in the diurnal cycle and which is maintained throughout fruit development. The rate of CO2exchange decreases on a fresh weight or surface basis, but increases with fruit ontogeny on a per fruit basis, causing accumulation of several percent CO2in the internal cavity. Stomata are present in the outer epidermis of those fruits examined, but with a 10‐to 100‐fold lesser frequency than in the abaxial epidermis of leaf of the same species. The number of Stomata is set at anthesis and remained constant, while the stomatal frequency decreases as the fruit surface expands. Stomata are as sensitive as in leaves in the early stages of fruit development, but often are transformed into lenticels during fruit ontogeny, thereby decreasing the permeability of the outer epidermis. The discrepancy between the CO2‐concentrating mechanism provided by PEPC analogous to C4/CAM Photosynthesis and the kinetics of fruit PEPC, characteristic of C3/non‐autotrophic tissue, suggests the definition of a new type of ‘fruit photosynthesis’ rather than its categorization with

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01914.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Cultivars of hexaploid wheat (Triticum aestivumcvs. Chinese Spring or PI 178704) and derivatives containing chromosomes from both a cultivar and a wild, salt‐tolerant species (Lophopyrum elongatumorL. ponticum) were compared to determine differences in growth, ion transport and ion accumulation under salt‐stress. Two experiments were conducted in which plants were grown under saline and non‐saline conditions and harvested at various lime intervals throughout ontogeny. Under salt‐stress the growth rate of the cultivars, as compared to the growth rate of the derivatives, decreased more rapidly later in development. Transport rates from root to shoot of Na+and Cl−reached higher levels in the cultivars. The cultivars accumulated more Na+and Cl−and relatively less K+in the shoot. The K+/Na+ratio was higher in the derivatives than in the cultivars from which they were derived. The addition of chromosomes fromLophopyrumspecies into wheat altered ion accumulation, growth rates, and ion transport rates from ro

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01915.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Sap expression, air drying and a combined technique were used to measure the water potential isotherm ofPinus ponderosaLaws, seedling shoots with the pressure chamber. Discrepancies between water relations parameters derived from these techniques can be partially explained by air entry into air drying tissues, hysteresis in the xylem water potential isotherm and dilution of apoplasmic solutes during sap expression.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01916.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Two models of the relationship between diurnal variation in shoot water potential and transpiration in 14‐year‐oldPicea sitchensis(Bong.) Carr. were compared. The first model was a physiologically based resistance‐capacitance (R‐C) analogue with its associated differential equations. The second was a non‐physiological discrete‐difference (D‐D) or stochastic transfer function model. The RC model included only the effect of water storage in the phloem and bark while the D‐D model implicity included all storage mechanisms. The R‐C and D‐D models explained similar fractions (62% and 68% respectively) of the variation in shoot water potential due to diurnal changes in transpiration rate. However, the D‐D model had fewer parameters than the R‐C model. The results from the D‐D model showed that the resistance to flow from soil to shoots along the trunk, (RT), was 5 × 103MPa kg‐1s and the capacitance of the phloem and bark treated as a single store, (Cs), was 1.6 kg MPa‐1. It is suggested that the resistance to flow into storage (Rs) is much greater than RTand can be disregarded. A non‐linear version of the D‐D model suggested [hat resistance to flow in the trunk increases

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01917.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Maize plants were grown in 1‐m‐long tubes of John Innes No. 2 potting compost. From the start of the experimental period, half of the plants were unwatered. Stomatal conductance of these plants was restricted 6 d after last watering and continued to decline thereafter. This was despite the fact that as a result of solute accumulation, unwatered plants showed consistently higher leaf turgors than well‐watered plants. Leaf water potentials of unwatered plants were not significantly lower than those of plants that were watered well. Main seminal and nodal roots showed solute regulation in drying soil and continued to grow even in the driest soil, and plants growing in drying soil showed consistently higher root dry weights than did well‐watered plants, water potentials and turgors of the tips of fine roots in the upper part of the column decreased as the soil dried. Soil drying below a water content of around 0–25 g cm−3(a bulk soil water potential of between ‐0.2 and ‐0.3 MPa) resulted in a substantial increase in the ABA content of roots. As soil columns dried progressively from the top, ABA content increased in roots deeper and deeper in the soil. These responses suggest that ABA produced by dehydrating roots and which was subsequently transported to the shoots provided a sensitive indication of the degree

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01918.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Two pollen species from theGramineaefamily were investigated as to their differential sensitivity to desiccation. Germinationin vivoceased to occur after previous drying to 7–8% moisture content inZea maysand 3% inPennisetum typhoides.The reduced vitality coincided with extensive membrane damage, as evidenced by the considerable leakage of fluorescein and K+from the prehumidified grains into liquid media. Further experiments were undertaken to investigate the basis for this interspecific difference: (1) phospholipid analyses revealed little difference in composition and content both before and after drying; (2) free fatty acid contents increased in both species upon drying but levels were generally low; and (3) sucrose was the sole soluble carbohydrate found in both species. Fresh maize pollen contained 5% sucrose, as compared to 14% inPennisetumpollen. During slow drying (8h) this level went up to 12% and 17%, respectively. Drying corn pollen in the cold (2°C), or at high rate, limited sucrose levels and affected the resistance to drying. The authors conclude that survival of dehydration is correlated with the presence of sucrose. Finally, they tested the ability of sucrose to preserve dry liposomes prepared from phospholipids purified from the two species. When liposomes were dried in the presence of sucrose, fusion and leakage could largely be prevented at mass ratio's of sugar to lipid of>4. Trehalose was also effective but myo‐inositol was not. No species differences were observed. The authors suggest that the presence of sucrose is a key factor in preserving membranes in dry po

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01919.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Leaching of inorganic cations (K+, Mg2+) and in some cases of inorganic anions and sugars from detached twigs and single needles of sprucePicea abiesL. Karst.) in the presence of acid rain (H2SO4, 1 mol m−3) or salt solutions (Na2SO4, 1 mol m−3) was examined under laboratory conditions. Cation leaching (as percentage of the total water soluble ion content of the tissue per hour) was: K+: 0.01‐0.02%; Mg2+: 0.005‐0.01%; Ca2+: 0.1‐0.2%. Leaching rates of anions were even lower than that and concentrations in the leachate were often below the detection limit of anion chromatography. Spraying with H2SO4(pH 2.95, 1 mol m−3) increased leaching only transiently. Similar effects were found when Na2SO4was used instead of H2SO4. The transiently enhanced leaching was apparently due to H+/cation or cation/cation exchange at the twig or leaf surfaces. Feeding of K+or Al3+through the stems increased leaching of all cations within a few hours, again demonstrating rapid ion exchange in the apoplast. Leaching of potassium and magnesium from single needles occurred at similar relative rates as from twigs. Loss of Ca2+ions, however, was even smaller from needles than from twigs. Apparently, a large part of the Ca2+lost from twigs originated from the bark and not from the needles. Efflux of ions from longitudinal needle sections was about 1000 times taster than the rates obtained with intact needles, indicating that the cuticle was the main barrier Preventing solute loss. In relation to the total amount of mineral nutrients in trees, leaching is considered to be too small to be the primary cause of damage to trees stressed by acid rain, as has been suggested in the

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01920.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Growth and gas exchange measurements are used to formulate a carbon balance model to describe the sorghum‐Striga hermonthicahost‐Parasite association.S. hermonthicareduces the growth and radically alters the architecture of infected sorghum plants. Grain and stem weight are reduced, whilst leaf and root biomass are maintained. Losses in host productivity result from two processes: export of carbon to the parasite and Parasite‐induced reductions in host photosynthesis. The latter occurs before the emergence of the Parasite above ground and accounts for 80% of the Predicted loss in production over the lifecycle of the association.S. hermonthicais dependent on carbon exported from the host, since the plant has low rates of photosynthesis coupled with high rates of respiration. Host‐derived carbon accounts for approximately one‐third of the total parasite carbon re

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01921.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Oenotheraplants grown as shoot meristem cultures on media having a low calcium concentration had a reduced abundance of raphides when compared to greenhouse‐grown plants or shoot meristem cultures grown on higher concentrations of calcium. Plants from the low‐calcium media also yielded a higher proportion of intact chloroplasts during subcellular fractionat

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01922.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY