摘要:

Abstract.The wood‐degrading white‐rot fungusPhanerochaete chrysosporium, has been the subject of intensive research in recent years and, based upon isolation of the extracellular enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood‐degrading fungi in general, attack l

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604752

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.The location and distribution of symbiotic bacteria during floral development inArdisia crispa(Thunb.) A.DC., a species characterized by bacterial leaf nodules, has been studied using light, scanning and transmission electron microscopy. During early floral development, bacteria in mucilage derived from host plant trichomes, become enclosed in a small conical chamber on top of the placenta, as a result of the closure and fusion of the carpel initials. The placental epidermal cells, which appear to be secretory in nature, become detached apically in places forming a network of grooves which traverse the placental surface. The symbiotic bacteria are preferentially located in these grooves. As growth and development of the placenta proceed, the grooves widen and deepen to form channels. The cells lining these channels secrete a mucilaginous material. The network of channels covers the entire placental surface and terminates at the placental margins surrounding the ovules. Bacteria are found within the channels, at the ends of the channels near the margin of the placenta, on the surface of the ovules and in the micropyle. It is suggested that these mucilage‐filled channels are responsible for, and a prerequisite of, ensuring that the bacterial partner is efficiently transmitted from one host generation to the next by providing a mechanism by which the bacteria arc accurately placed within the developing see

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604753

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen content. The method predicts glucose equivalents, the amount of glucose required to provide carbon skeletons and reductant to synthesize a quantity of organic product. Glucose equivalents have previously been calculated from the elemental composition of tissue. We define construction cost as the amount of glucose required to provide carbon skeletons, reductant and ATP for synthesizing the organic compounds in a tissue via standard biochemical pathways. The fraction of the total construction cost of a compound or tissue (excluding costs of transporting compounds) that is reflected in its glucose equivalents is the biosynthetic efficiency (EB). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total construction cost can be estimated to ± 6% of the value obtained from biochemical pathway analysis.Construction costs of leaves of three chaparral species were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differences were probably due to a combination of inaccuracy in the estimated biosynthetic efficiency and technical difficulties with biochemical analysis, one of the older methods of determining construction cost

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604754

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.The interrelationships of leaf diffusive conductance, tap root cell turgor pressure and the diameter of the tap root of sugarbeet were studied. The study was conducted on well‐watered plants growing in pots under artificial light in the glasshouse. In a typical experiment, on illumination (400 μmol m−2s−1) leaf conductance increased from 0.6 to 7.4 mm s−1. Cell turgor pressure in the tap root decreased from 0.8 MPa to 0.45 MPa and the root diameter (9.0 cm) contracted by 145μm. Removal of light resulted in the reversal of each of the above parameters to their previous values. Quantitively similar results were obtained when sugar beet plants were uprooted and the response of each of the parameters was measured. The sequence of events however was different. On stimulation by light, changes in leaf diffusive conductance preceded the turgor and root diameter changes (which were simultaneous) by some 15–20min. In contrast, on uprooting the simultaneous changes in root turgor pressure and diameter preceded the changes in leaf conductance. The lag times between changes in diffusive conductance and turgor pressure in the root were between 20 and 30 min.Tap root turgor pressure and diameter correlated strongly and permitted the calculation of an apparent whole root volumetric elastic modules (55–63 MPa). The small changes in tissue volume relative to the transpiration rate suggest that the tap root is not a significant source of transpirational water d

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604755

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.Total RNA was extracted from bean leaf abscission zones at different times after the induction of abscission by ethylene. The RNA was translated in the wheat germ system and the products analysed by SDS‐PAGE. Products of molecular weight (raw) 42, 32 and 17 kD were seen to accumulate substantially during the induction. An attempt was made to establish that the mRNA species which produced the 32 kD product, which was coded for the ethylene‐regulated enzyme chitinase. Mature chitinase (30 kD) was purifed from ethylene‐treated abscission zones and used to raise monospecific antibodies in rabbits. These antibodies recognized the 32 kD product and mature chitinase. The 2 kD difference in molecular weight was due to the presence of the signal sequence which could be removed by microsomal membranes. Chitinase was also detected by enzymatic assay and immunoblotting of crude homogenates from ethylene‐treated abscission zones. Chitinase appears to be ubiquitous in bean plants and probably does not have a direct role in abs

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604759

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.The effect of photoinhibition on the activity of photosystem II (PSII) in spinach chloroplasts was investigated. Direct light‐induced absorbance change measurements at 320 nm (ΔA320) provided a measure of the PSII charge separation reaction and revealed that photoinhibition prevented the stable photoreduction of the primary quinone acceptor QA. Sensitivity to photoinhibition was substantially enhanced by treatment of thylakoids with NH2OH which extracts manganese from the H2O‐splitting enzyme and prevents electron donation to the reaction centre. Incubation with 3‐(3,4,‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) during light exposure did not affect the extent of photoinhibitory damage. The chlorophyll (Chl)b‐less chlorina (2 mutant of barley displayed a significantly smaller light‐harvesting antenna size of PSII (about 20% of that in wild type chloroplasts) and, simultaneously, a lower sensitivity to photoinhibition. These observations suggest that photoinhibition depends on the amount of light absorbed by PSII and that the process of photoinhibition is accelerated when electron donation to the reaction centre is prevented. It is postulated that the probability of photoinhibition is greater when excitation energy is trapped by P680+, the oxidized form of the PSII reaction centre. The results are discussed in terms of the D1/D2 heterodimer which contains the functional PSII components P680, pheo

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604761

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.The effect of short‐term SO2fumigation on photosynthesis and transpiration ofVicia fabaL. was measured at different irradiances and SO2concentrations. At high irradiances photosynthetic rates were reduced when leaves were exposed to SO2and the magnitude of the reduction was linearly related to the rate of SO2uptake through the stomata. Photosynthetic rates stabilized within 2 h after the start of fumigation.The effect of SO2on photosynthesis was measured at different CO2concentrations to analyse the contribution of stomatal and non‐stomatal factors to photosynthetic inhibition. Mesophyll resistance to CO2diffusion increased as a result of SO2exposure and caused a rapid reduction in photosynthesis after the start of fumigation. Stomatal resistance was not affected directly by SO2fumigation, but indirectly as a result of a feedback loop between net photosynthesis and internal CO2concentration.Analysis of gas‐exchange measurements in biochemical terms indicated that photosynthetic inhibition during SO2exposure can be explained by a stronger reduction in the affinity of RBP carboxylase/oxygenase for CO2than f

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604762

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.Kalanchoë daigremontianastrongly reduced daily water loss within 6 d of drought using CAM to restrict transpiration and net CO2uptake to the dark period.Water translocation from old to young leaves of the plant was an additional mechanism which reduced the negative effects of drought on the water relations of young leaves. Excision of old leaves after 7–9 d of drought resulted in a decrease in the water content of young leaves. This was observed despite a decrease in transpirational water loss from young leaves. Water content in young leaves increased slightly in plants with all their leaves in place.The dry weight of young leaves clearly increased during the experimental period when old leaves were present, but it remained relatively constant in plants without old leaves. Obviously, in addition to water, solutes were transported from old to young leaves of the plant via the phloem. Xylem tension was higher in young compared to old leaves; thus, water translocation could have occurred via xylem elements.Since transport of organic matter in the phloem is also linked to water flow, phloem transport additionally may contribute effectively to the balance of the water budget in young leav

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604763

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.Environment and plant measurements were made to determine what factors may limit growth of deepwater and floating rice plants during partial or complete submergence. Field surveys included measurements of temperature, pH, light, O2and CO2in floodwater in Thailand. In addition, measurements were made of O2and CO2concentrations inside internodal lacunae of deepwater and floating rice growing at 0.5–2.0 m water depths.The bulk of measurements were taken during periods when the changes in water level were less than 50 mm d−1. In the 0–0.02 m surface layer of floodwater at any location there were large changes in oxygen concentrations over diurnal cycles: there were decreases during the night down to 0.02–0.18 mol m−3O2at 0600 h and increases during the day to 0.13–0.28 mol m−3O2at 1500 h (0.28 mol m−3being 120% of the O2concentration of air saturated water at 30°C). During the day oxygen concentrations decreased with increasing water depth; concentrations just above the soil surface were occasionally zero. Most of this gradient disappeared during the night, and at dawn the 0.6 m surface layer of water had uniform low O2concentrations.O2concentrations were also measured during flash floods in Thailand. In contrast to the conditions with only small increases in water level, the O2concentrations in the water during flash floods were more uniform with depth and changed little over a diurnal cycle, the O2ranging between 0.14–0.19 mol m−3.In most locations floodwater contained 0.2–1.9 mol m−3CO2and 0.7–1.6 mol m−3bicarbonate; however, in a location with acid sulphate soil CO2was only 0.05–0.2 mol m−3, and bicarbonate concentrations were several fold lower. Concentrations of CO2in floodwater increased with increasing water depth.O2and CO2concentrations inside internodal lacunae of rice were determined in the field when water depth were 1–2 m. Concentrations of O2in internodes at the water surface were 16–20%, and decreased to 10% and 5% at 0.8 and 1.8 m water depth respectively. There was no diurnal cycle in O2concentrations inside internodes. In contrast, CO2concentrations in the lacunae increased with water depth and ranged from 1–3% in internodes at the water surface to 5–10% in internodes at 1.8 m water depth. There was evidence for a diurnal cycle in CO2concentrations in the basal internode near the soil surface, CO2increased during the day and decreased during the night.The above data are used to show that there is little or no relationship between gas concentrations in floodwater and internodal lacunae of rice plants. Results are discussed in relation to O2supply to submerged portions of rice and metabolism

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604764

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.Heat balance methods of stem flow measurement offer the opportunity to measure directly the mass flow rate of water in plants. We have tested one such approach; the constant power heat balance method of Sakuratani (1981). The results supported his statement of an approximate accuracy of 10% when measuring the transpiration rate of herbaceous plants. The response to sudden changes in stem flow rate is not instantaneous, but investigation of the time constant shows that it decreases as stem flow increases, to the extent that, at flow rates typical of daytime conditions the system is capable of accurately tracking changes in stem flow within 5 min or less.We describe a new gauge design that is relatively rugged, simple to use with an appropriate digital datalogger and suitable for field use over prolonged periods of time. It does not injure or penetrate the stem, is amenable to continuous and direct recording of the mass flow rate of water in the stem and requires no calibration. A further refinement, which should improve both the accuracy and the dynamic response of the system, is proposed.

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604765

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY