摘要:

Abstract.Gas exchange measurements were performed to test the hypothesis that failure of stomata to open in senescing leaves ofNicotiana glaucais caused by elevated concentrations of carbon dioxide in the intercellular spaces of leaf mesophyll tissue (ci). Senescing leaves selected for experiments were completely chlorotic and lacked positive rates of photosynthesis. When stomata in detached epidermis from senescing leaves were illuminated in CO2‐free air, they opened to similar apertures as those in detached epidermis from nonsenescing leaves. To compare the effects of changes in cion stomatal responses of the two leaf types, leaf ‘flags’ of either nonsenescing or senescing leaves were illuminated at a photosynthetic photon flux density of 500 μmol m−2s−1in a gas exchange cuvette. Leaf temperatures were maintained at 23.5 ± 0.5°C, and vapour pressure differences between leaves and the air were maintained between 0.70 and 0.75kPa. Ciwas adjusted by changing external concentrations of carbon dioxide in air circulating through the cuvette. Conductances and photosynthetic rates of nonsenescing leaves changed in response to changes in ci, but neither the conductances nor the photosynthetic rates of senescing leaves were affected significantly by changes in q. We conclude that guard cells of senescing leaves ofNicotiana glaucado not lose the capacity to respond to changes in carbon dioxide concentration and that increases in ciresulting from declining rates of mesophyll photosynthesis are not the sole cause of maintenance of stomatal closure during leaf senescence. The data suggest that factors external to guard cells may prevent them from responding to changes in carbon dioxide concentrations in intact sene

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00967.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The root systems of 30‐d‐old sunflower plants were treated with polyethylene glycol (PEG; osmotic potential ‐ 1.0MPa) for 2h, causing mild and transient wilting. Ten minutes before this treatment was applied, half the plants were defoliated. At varying times after the imposition of the PEG ‘drought stimulus’, the plant stems were cut and the sap exudate was collected and analysed for abscisic acid (ABA), using an elisa method. When stems were cut 2.25h after the treatments were applied, the ABA concentration in the sap of the controls did not vary with time: the mean concentration was 10.7 ± 1.0μ, mol m−3. However, in the treated plants, the first sample contained 78.1 ± 10.1 μmol m−3, decreasing to 13.6 ± 2.8 μmol m−3over 8.75h. Defoliation did not affect the ABA concentration in the sap. When stems were cut atvaryingtimes (up to 25h) after treatment, the PEG treatment again caused an immediate increase in the ABA concentration in the sap, from 20 ± 1 to 136 ± 21 μmol m−3. However, defoliation reduced this increase, but only in plants sampled 4–25h after treatment. We conclude that, after the PEG treatment to the roots, the initial increase of the ABA content of sap, and its attenuation with time, may be ascribed to synthesis in the roots whereas, thereafter, ABA derived from the leaves makes a major contribution to th

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00968.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Flux densities of water vapour and carbon dioxide were measured for a Mediterranean macchia canopy. Results show good agreement between the measured available energy and the sum of latent sensible and heat flux densities determined with the eddy correlation technique. Joint evaluation of the Bowen ratio, aerodynamic resistance, canopy resistance and the ‘omega factor’ suggests that the macchia canopy is intermediate in aerodynamic roughness between coniferous and deciduous canopies. Maximum daytime carbon flux densities ranged from ‐14 to ‐22(μnol m−2s−1on a ground area basis. The ratio of transpiration to assimilation (E/A) was a function of incident photo‐synthetic photon flux density below about 400 μmol m−2s−1and above it was fairly constant at 272 mol mol−1(H2O/CO2). The relationship between carbon influx and canopy conductance was linear. Results show promising applications of the eddy correlation technique for evaluating physiological features of canopies, treated as unita

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00969.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.We report two situations in which the polarity of gravitropism of single protonemal cells of the mossPhyscomitrella patensis reversed. Dark‐grown protonemata of wild‐typeP. patensgrow negatively gravitropically. Time‐lapse video‐microscopy reveals that a temporary reversal of growth polarity occurs during mitotic division which is independent of the cells’ growth rate. A transitory reversal of growth direction is also observed when the unidirectional gravitropic stimulus is interrupted by a period of growth on a clinostat. A third situation, in which a mutant class responds by growing positively gravitropically, has been described previously (Jenkins, Courtice&Cove, 1986). These observations are discussed in terms of possible mechanisms for cell morphogenesis and trop

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00970.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.While a short‐term exposure to elevated atmospheric CO2induces a large increase in photosynthesis in many plants, long‐term growth in elevated CO2often results in a smaller increase due to reduced photosynthetic capacity. In this study, it was shown that, for a wild C3species growing in its natural environment and exposed to elevated CO2for four growing seasons, the photosynthetic capacity has actually increased by 31%. An increase in photosynthetic capacity has been observed in other species growing in the field, which suggests that photosynthesis of certain field grown plants will continue to respond to elevated levels of atmospheric

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00971.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A temperate grassland model has been used to simulate carbon sequestration under various environmental conditions. The results suggest that the CO2and nitrogen fertilization that has occurred may contribute appreciably to the so‐called missing carbon sink, which it has been suggested must exist to balance the global carbon budge

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb00972.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY