摘要:

Abstract.The authors examine the isotopic composition of leaf water, at natural abundance levels, as influenced by transpiration rate. The isotopic composition of water of wheat leaves (Triticum aestivumL. var. Aroona) was followed while their transpiration rate adjusted to ‘steady‐state’ environmental conditions. Leaf diffusive resistance was modified by short‐term salt treatment and by plant culture in either nutrient solution, free‐draining sand, or vermiculite. Resultant changes in18O and2H in leaf water are described and fitted to the model of Leaneyet al.(1985). The treatments with lower transpiration rates were found to have a greater fraction of their leaf water equilibrated with water vapour in the atmosphere. Comparable results were obtained with both18O and2H, with some differences being interpreted in terms of turbulence in the vapour diffusion path. The fraction of the leaf water equilibrated with the atmosphere varied between leaves of different ages. However, this may have been due to their different positions in t

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01937.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Analysis is made of leaf numbers observed in the field for several wheat genotypes over a wide range of sowing dates. Within any treatment, leaf number was a linear function of thermal time from seedling emergence (°C.d, the mean daily temperatures summed above a base temperature of 0°C) but the slope of the relation depended on sowing date. Leaf appearance rate doubled from October to February sowings, for which it was maximum, and usually decreased for later sowings. However, when expressed on the basis of photothermal time (°C.dl, temperatures accumulated during the light time period only), much of the sowing date effect was removed, except for the latest spring sowings. For these late sowings, leaf appearance rate was usually slower than expected. The authors conclude that both temperature and photoperiod are determinants of leaf appearance rate, and suggest that the slow rate for late sowings may be caused by a non‐linear response to the higher temperatures experienced by the plant during that part of the year. The genotypic differences indicate that it may also be associated with a lack of vernalization. The use of photothermal time rather than thermal time significantly improves prediction of leaf number. However, it still provides only an empirical description of the dependence of leaf number on time and cli

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01938.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The internal parenchyma of the leaf and rhizome in 36 species ofSansevieriais made of dead cells and living cells arranged in a regular pattern. Intercellular spaces are lacking. The walls of dead cells consist of an inner amorphous layer positive to the fluorescence test for callose, a middle suberin‐like layer and an outer fibrillar layer. In about half of the species examined, the inner layer forms distinctive thickenings. Detached leaves ofSansevierialose water very slowly, and are able to recover it quickly. The pattern of leaf dehydration appears to be related to leaf morphology, whereas no relation is evident between the pattern of leaf rehydration and leaf morphology. Neither leaf dehydration nor leaf rehydration pattern is affected by the presence of wall thickenings in the dead parenchyma cells. The fresh weight per unit volume of both turgid and droughted leaves is nearly 1, denoting that the dead cells are filled with water and do not undergo substantial cavitation during drought. The data indicate that the dead parenchyma cells ofSansevieriaare a specialized water‐storing sys

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01939.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The objective of the present work was to study the effect of nitrogen deficiency on drought sensitivity of tall fescue plants. The authors compared photosynthetic and stomatal behaviour of plants grown at either high (8 mol m−3) or low (0.5 mol m−3) nitrogen levels during a drought cycle followed by rehydration. Other processes investigated were stomatal and non‐stomatal inhibition of leaf photosynthesis, water use efficiency and leaf rolling. Plants were grown in pots in controlled conditions on expanded clay. A Wescorin situhygrometer placed on the leaf base outside the assimilation chamber permitted, simultaneously to leaf gas exchange measurements, monitoring of leaf water potential. Drought was imposed by withholding water from the pot. CO2uptake and stomatal conductance decreased and leaves started to roll at a lower leaf water potential in the high‐N than in the low‐N grown plants. Stomatal inhibition of leaf photosynthesis seemed larger in the low‐N than in the high‐N plants. Water‐use efficiency increased more in the high‐N than in the low‐N grown plants during the drought. The decrease of photosynthesis was largely reversible after rehydration in low‐N but not in high‐N leaves. The authors suggest that low‐N plants avoid water defici

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01940.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Identification of the cytokinin complex of primary crown gall tumours of tomato (Lycopersicon esculentumL.) by combined gas chromatography‐mass spectrometry has been described. Several cytokinins have been identified which included zeatin, dihydrozeatin, isopentenyladenine, and their respective riboside and nucleotide derivatives. In addition, 6‐benzylaminopurine, its riboside and the corresponding nucleotide have also been identified as major endogenous compounds in this tissue. This would appear to be the first report on the identification of cytokinins from a primary crown gall tumour tissue using unequivocal meth

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01941.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.White lupin (Lupinus albusL.) was grown for 13 weeks in a phosphorus (P) deficient calcareous soil (20% CaCO3, pH(H2O)7.5) which had been sterilized prior to planting and fertilized with nitrate as source of nitrogen. In response to P deficiency, proteoid roots developed which accounted for about 50% of the root dry weight. In the rhizosphere soil of the proteoid root zones, the pH dropped to 4.8 and abundant white precipitates became visible. X‐ray spectroscopy and chemical analysis showed that these precipitates consisted of calcium citrate. The amount of citrate released as root exudate by 13‐week‐old plants was about 1 g plant−1, representing about 23% of the total plant dry weight at harvest. In the rhizosphere soil of the proteoid root zones the concentrations of available P decreased and of available Fe, Mn and Zn increased. The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the rhizosphere leading to intensive chemical extraction of a limited soil volume. In a calcareous soil, citric acid excretion leads to dissolution of CaCO3and precipitation of calcium citrate in the zone of proteoi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01942.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The supply of oxygen to respiring shoot tissue was investigated for three submerged macrophytes (Potamogeton crispusL.,Egeria densaPlanch, andMyriophyllum triphyllumOrchard). For all species, the response of oxygen uptake rates to the external O2concentration was a rectangular hyperbola over the range 0–5.0 × 10−3m3m−3. However, the response pattern for material with water‐infiltrated lacunar airspaces was non‐hyperbolic over this range. The change in response was interpreted as an increased substrate (O2) limitation, resulting from lower radial diffusion rates within the infiltrated material. Neither the uninfiltrated nor the infiltrated responses obeyed the linear and logarithmic formulae of the type observed for submerged macrophytes by earlier authors. These results suggest that the responses observed are affected by factors such as water velocity, internal restrictions to diffusion and the range of oxygen tensions investigated. Therefore, it is unlikely that one response formula can adequately account for the effects of oxygen concentration on submerged macrophyte oxygen uptake. The lacunar airspaces also represent a possible oxygen source for dark respiration. The consumption of oxygen from the airspaces was investigated by displacing the gas from the lacunae and measuring the subsequent increase in the rate of oxygen assimilation from the external liquid. Approximately 30% of the oxygen consumed byE. densaandP. crispus, and more than 40% of that consumed byM. triphyllum, was derived from the lacunar system. This O2supply is a consequence of the higher oxygen concentration in the lacunae than in the external medium, due to the low solubility of oxygen in water. Storage of photosynthetically‐produced oxygen in the lacunae could not be identified during a light/dark transient, due to rate changes caused by the effects of light on the respiratory metabolism. However, O2partial pressure gradients artificially set up between the lacunae and water equilibrated within an hour, suggesting that excess oxygen would be lost to the water with

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01943.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.Seasonal data on leaf conductance (gl) for three different apple cultivars grown in four separate orchards with different aged trees was studied between 1979 and 1985. A number of empirical models for predicting leaf conductance from environmental measurements were compared using this data and a general method for adapting such models for the prediction of different data sets is proposed. Although stepwise multiple regression identified relative humidity or vapour pressure as important variables, it frequently did not identify the optimal set of independent variables, which often did not include either of these. There was no advantage in regressing glagainst principal components of the environment, rather than against the raw environmental variables. A simple model involving air vapour pressure deficit, air temperature and a hyperbolic function of irradiance was found to explain between 32 and 62% of the variance in glfor the different data sets. Parameters fitted for one data set led to the effective prediction of glin other years or plots. The model fit could generally be improved significantly by including soil moisture deficit among the independent variables.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01944.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The effect of plant competition on spectral reflectance in the 400–2500 nm wavelength region was determined for 3‐month‐old and 15‐month‐old leaves of loblolly pine (Pinus taedaL.). Strong competition decreased water potentials and Mg concentrations, and increased K in young and old leaves. Also, competition decreased Ca and total chlorophyll in young leaves. As measured with a scanning radiometer, reflectance in young leaves at 551 nm decreased from 20 to 14% as water potentials increased from ‐2.2 to ‐0.9 MPa (r2= 0.82). For young and old leaves reflectance at 551 nm decreased from 20 to 10% with increasing total chlorophyll (r2= 0.64). Reflectance decreased slightly with increasing K in young leaves (401 nm, r2= 0.55), and with increasing Mg in old leaves (470 nm, r2= 0.57). Increased visible reflectance under strong competition may have resulted primarily from decreased water potentials. Reflectances were much greater in young versus old leaves in the 750–1300 nm range, and were greater in old rather than young leaves from 1400–2500 nm. Infrared reflectances were not, however, significantly affect

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01945.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract.The relative growth rates and leaf area were graphed against leaf area, normalized with respect to final leaf area, to assess the applicability of the Lockhart cell wall expansion equation to soybean,Glycine max(L.) Merr., leaf development under field conditions. For leaves that had completed more than 20% of their growth, relative growth rates decreased linearly with an increase in the normalized leaf area, indicating that these leaves were undergoing strictly expansive growth. Drought stress significantly decreased the relative growth rate of these larger leaves. Small leaves which had completed less than 20% of their growth, were found to have highly variable relative growth rates. The large variability in relative growth rates indicated that the Lockhart cell wall expansion equation was inadequate to evaluate the growth of these young leaves. Drought stress had virtually no influence on the relative growth rates observed in the small leaves.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01946.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY