摘要:

AbstractThere has been little written on the penetration of light through soil. In this review, we attempt to collate most of the work that has been published on this topic in order to stimulate further research and to clarify the often‐confused literature.Light penetration can be measured directly with, for example, a spectroradiometer, or indirectly by using germination of light‐sensitive seeds or the presence of growing algae as bioindicators. Although the penetration of light through soil is greatly affected by factors such as soil moisture content and particle size and colour, it generally appears that physiologically and ecologically significant amounts of light rarely penetrate more than 4–5 mm through the soil, and may often penetrate much less than this. Any penetration beyond 10 mm would generally not be significant, especially as most soils are covered with litter, algae or lichens, or are shaded from direct sunlight. However, for some light‐stimulated geo‐tropic responses of roots, which can be sensitive to very low fluences, the penetration of light to greater depths could well be significant. The role of light in soil in directing root growth is also

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01607.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractQuantum yields of photosynthetic CO2uptake byPinus sylvestris(L.) shoots were measured at temperatures between −; 2°C and 35°C from September 1984 to September 1985. The ratio of variable to peak fluorescence of photosystem II (Fv/Fp) was also measured. Quantum yield measured at 25°C varied with time from a low winter value of 0.017 to a high summer value of 0.057. This variation was strongly correlated to variation inFvFp(r2= 0.91).The response of quantum yield to temperature changed with season. During winter, quantum yield was essentially constant between 0°C and 35°C. The constancy above 5°C was associated with a strong increase in intercellular space CO2(Ci) with temperature. In June, the quantum yield peaked at 5°C, decreased sharply below 5°C, and was rather constant between 25°C and 35°C. This insensitivity to increased temperature above 25°C was attributed to a large increase inCiIn contrast, by September, the quantum yield was less sensitive to temperature below 5°C and more sensitive above 25°C, despite an unchangedCiresponse with increasing temperatures as compared with June. In August, quantum yields were lowered at 0, 5 and 15°C, apparently as a result of high carbohydrate levels in the leaves. Overall, the results suggest that there are sites other than in photosystem II or at ribulose bisphosphate carboxylase/oxygenase at which the quantum yield of photosynthetic CO2uptake is affected. Possible causes for the changes in efficienc

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01608.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractXylem cell walls were isolated from internodes of tomato plants (Lycopersicon esculentumMill, cv. Tiny Tim). Purification was carried out in Triton X‐100. Experiments were conducted in which the adsorption of Cd2+(applied as115CdCl2) in the cell walls was measured. The application of γ‐γ‐directional correlation measurements permitted the direct determination of chemically bound cell wall Cd in experiments where the total adsorption of Cd was also measured. A set of equations is presented by which the adsorption of Cd could be described, thereby considering the presence of co‐ions in the polyelectrolyte phase. In experiments with simultaneousll5CdCl2and K82Br applications, measurements were carried out of the presence of82Br−in the Donnan Free Space (DFS), indicating Cl−action in the process of CdCl2adsorption.The cell wall contents of the relevant ions were determined in such a manner that the measurements gave access to the undisturbed equilibrium concentrations. The very small Br−concentrations in the DFS indicated that, at small applied concentrations, internal free Cd may be considered to exist entirely of Cd2+. The results suggest that simultaneous measurement of internal free counter‐ion and co‐ion concentrations may be a relatively easy way to check the reliability of values for apparent formation constants in single cation adsorption experiments. From experiments in which the cell walls were incubated in solutions of varying Cd concentrations, the apparent dissociation constant (KCd2+) for the formation of R2Cd complexes could be calculated as 51±6 mol m−3. The exchange coefficient (KCd2+H+) was shown to vary with the internal free proton concentration and the applied Cd2+concentration, due to the buffering capacity of the car

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01609.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe changes in growth rate during phototropism in light‐grown mustard (Sinapis albaL.) seedlings have been investigated to clarify the pattern of differential growth which causes curvature. It is shown that deliberately induced phytochrome‐mediated straight‐growth responses can modify the pattern of differential phototropic growth. A comparison of techniques used to analyse phototropic responses in mustard shows that separate light‐growth responses can explain the contradictory published data. When white light is moved from above to one side, straight‐growth responses not mediated directly by the blue photo‐receptor are induced by an increase in the amount of light within the hypocotyl, and these modify the pattern of differential growth. In the absence of such separate light‐growth responses, phototropism is caused by a redistribution of growth within t

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01610.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractPrevious work with clones ofPopulus trichocarpademonstrated that the water vapour conductance of leaves from well‐watered cuttings of this species does not decline with loss of turgor from the bulk leaf. In the present study, stomatal responses to water potential inPopuluswere examined with detached epidermal strips. Stomata in epidermal strips from well‐watered plants ofP. trichocarpadid not close at low water potentials which led to plasmolysis of the guard cells. In contrast, stomata ofP. deltoidesand aP. trichocarpa×deltoideshybrid closed when the guard cells lost turgor. A period of water stress preconditioning resulted in modified stomatal responses inP. trichocarpasuch that stomata of stressed and re‐watered plants nearly closed when guard cell turgor wa

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01611.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractSaxifraga cernua, a perennial herb distributed throughout the arctic and subarctic regions, shows high levels of dark respiration. The amount of respiration exhibited by leaves and whole plants at any temperature is influenced by the pretreatment temperature. Plants grown at 10°C typically show higher dark respiration rates than plants grown at 20°C. The levels of alternative‐pathway respiration (or cyanide‐insensitive respiration) in leaves ofS. cernuagrown at high and low temperatures were assessed by treating leaf discs with 0.25 mol m−3salicylhydroxamic acid during measurements of oxygen consumption. Alternative pathway respiration accounted for up to 75% of the total respiration. Tissues from 20°C‐grown plants yielded a Q10of 3.37 for normal respiration, and of 0.97 for alternative‐pathway respiration. Tissues from 10°C‐grown plants yielded a Q10of 2.55 for normal respiration, and of 0.79 for alternative‐pathway respiration. The alternative pathway does not appear to be as temperature sensitive as the normal cytochrome pathway.A simple energy model was used to predict the temperature gain expected from these high rates of alternative‐pathway respiration. The model shows that less than 0.02°C can be gained by leaves experiencing these hi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01612.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractDuring the first 5 d of germination in the presence of exogenousl5NO−3and the inhibitor of nitrification N‐SERVE, the nitrogen reserves of the caryopses ofZea maysL. were found to account for 75% of the total nitrogen content of the developing seedlings. During this period, an increasing pool of14NO−3was detected in both the grain and the seedling. The accumulation of nitrate in the grain and the extent of hydrolysis of seed reserves were enhanced when nitrate was removed from the growing medium. The significance of a possible oxidative pathway from reduced nitrogen to nitrate is disc

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01613.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effect of freezing night temperatures on net photosynthesis, stomatal conductance, and internal CO2concentration was investigated in unhardened seedlings of Engelmann spruce. Exposure to – 2.5°C in the dark for 10 h caused a slight and reversible reduction in gas‐exchange parameters on the following days. Substantial and irreversible inhibition of photosynthesis occurred after exposure to ‐4°C or –5°C. Despite a parallel decline in stomatal conductance and net photosynthesis, exposure to a hard freeze caused a decrease in the stomatal limitation to gas exchange. Hard‐freeze conditions (less than – 4°C) also caused a decrease in carboxylation efficiency and apparent quantum yield, indicating a freeze‐induced failure of the dark reactions and electron transport. There was no significant difference in the photosynthetic response to freezing temperatures in different elevational populations of spruce, although acclimatory adjustments were observed. Gas exchange in seedlings grown under cool conditions (14°C day/9°C night) was less affected and recovered more rapidly after exposure to a hard freeze than in seedlings grown under warm conditions (2

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01614.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to determine the respective extents to which winter reduction of photosynthetic capacity in ivy (Hedera helixL.) is caused by direct frost injury to the photosynthetic apparatus and by preceding protoplasmic changes connected with the acquisition of frost tolerance. Potted juvenile ivy plants were placed in the open under natural weather conditions whilst others were hardened under controlled conditions and subjected to the desired frost stress.Low non‐freezing temperatures induced frost tolerance in ivy leaves down to about – 12°C (50% injury = TL50) without impairing net photosynthetic rate as measured under standard conditions (20°C, light saturation, natural CO2level; = Standard‐Fn. Only if the leaves froze (below − 3°C to −4°C) was a reversible inhibition of Standard‐Fnobserved. As long as the temperatures did not fall below approximately −8°C the inhibition was small and Standard‐Fnreached about 80–90% of the control. In this case the stomatal opening narrowed, giving a poorer supply of CO2to the mesophyll cells. Maximal frost tolerance (TL5O−20°C to −24°C) developed only with severe frosts below about − 10°C. After such frosts, Standard‐Fnwas reduced to less than 20% of the control. The dependence of the rate of net photosynthesis on the internal CO2concentration showed a lower initial slope, thus indicating disturbances of chloroplast functions. However, neither in outdoor plants nor in those artificially frosted at – 20°C could there be found an appreciable inhibition of the electron transport capacity from H2O to dichlorophenol indophenol or of ribulose bisphosphate carboxylase.If intact, severely frosted ivy plants were then held at higher temperatures (20/15°C), Standard‐Fnrecovered completely in approximately 10 d. Furthermore, following a frost period with temperatures down to −12°C, mild weather caused a distinct improvement in Standard‐Fnin outdoor plants, and there was no loss of maximum frost tolerance. Thus it can be concluded that the inhibition of Standard‐Fnafter severe frosts is not due to the development of maximal frost tolerance, but rather may be attributed t

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01615.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe ethylene‐releasing compound 2‐chloroethylphosphonic acid (ethephon) stimulates germination of dormant seeds under laboratory conditions and it may prove to be an effective means of administering ethylene to promote germination of seeds in the field. We examined the decomposition of ethephon in different soils to determine which properties of soils influence the activity (ethylene release) of ethephon. The release of ethylene from ethephon was not affected by the type of soil, the texture, the presence of organic matter, or levels of extractable SO2−4, PO3−4NO−3, K+or Na+. The rate of decomposition was, however, dependent on soil pH and was influenced by the soil moisture content. Very little ethylene was released from ethephon in soils with a pH<7.7 and with a moisture co

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1987.tb01616.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY