ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01332.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYExtinction of local populations of plants of many biennial plant species has been frequently reported. Survival of these species on the meta‐population level implies a balance between extinction and regeneration, either through seed dispersal or from the seedbank. We distinguish between three types of biennials (transient, fugitive and persistent) and review the relation between dynamics of local populations and habitat characteristics, such as disturbance. Some species are safe‐site limited whereas other species demonstrate a combination of safe‐site and seed limitation. Meta‐population dynamics are illustrated with two examples (Senecio jacobaeaandCynoglossum officinale). We distinguish between patch dynamics (loss and genesis of sites that are suitable for population development) and meta‐population dynamics of biennials (population behaviour within and between sites, and dispersal). A hypothesis is developed on the regulation of patch dynamics. Finally we discuss the question: what makes biennials suited for exploiting temporary

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01333.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYTwo clones of the grassHolcus lanatusfrom a metal‐contaminated (Hallen Wood, Avonmouth, UK) and an uncontaminated site (Totley, Sheffield, UK) accumulated cadmium from Cd‐amended hydroponic cultures, the Totley material to two‐fold higher concentrations than the Hallen Wood. The Totley clone showed impaired growth at relatively low Cd concentrations; the reduction in parallel tolerance indices (TIs) to 50% occurred at an external Cd concentration of 53 μM compared with 94 μM in the Cd‐tolerant Hallen Wood material. In both clones Cd was transported to the shoots; in the non‐tolerant (Cd‐sensitive) Totley tissues the two‐fold greater Cd accumulation was accompanied by a two‐fold rise in lipid peroxidation, indicative of membrane damage by reactive oxygen species in the shoot, though not in the roots. Evidence for the involvement of activated forms of oxygen was also seen in the highly significant correlations between Cd uptake into the shoot and the activities of superoxide dismutase (r= 0·95) and guaiacol peroxidase (r= 0·96), but confined to the sensitive Totley material. It was concluded that one potentially highly‐damaging effect of Cd was to promote the generation of partly‐reduced and highly‐reactive forms of oxygen in the Cd‐sensitive clone and that the site of activated oxygen formation was the

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01334.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYEthylene, a lipid‐soluble gas, is known to have considerable effects on plant metabolism. It is possible that some of these metabolic effects are the result of ethylene's lipid solubility. The effect of low concentrations of 2‐chloroethylphosphonic acid (ethrel), an ethylene‐releasing compound, on the susceptibility of artificial membrane vesicles (liposomes) to phospholipase A2and phospholipase C was studied. Liposomes were found to be more susceptible to degradation by these two phospholipases in the presence of ethrel. Ethrel promoted maximal degradation of liposomes by phospholipase C at a concentration of 55 nm. Ethrel also enhanced the leakiness of liposomes tol‐leucine only in the presence of phospholipase A2. The rate of degradation of liposomes by both phospholipases was enhanced by about 20–30% in the presence of ethrel. The results may indicate that ethylene may affect the accessibility of phospholipases to their target sites within the lipid bilayer of artificial membrane

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01335.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYThe response of three bean (Phaseolus vulgaris) cultivars to 10 mg 1−1Al in nutrient solution was studied using tolerance indicies based on root elongation, root dry weight, shoot dry weight and leaf expansion growth. Plant Al and Ca concentrations were determined. According to the tolerance index based on root elongation, the cultivars Hilds Maxi and Selección F‐15 were Al tolerant, while Eagle was Al sensitive. Aluminium supply significantly affected shoot growth in Selección F‐15 and this cultivar exhibited unusually high Al concentrations in shoots. Eagle, the most Al‐sensitive cultivar, was able to restrict Al uptake and transport. In the presence of Al, calcium uptake was significantly decreased in all cultivars. Scoring for tolerance using root elongation as a single criterion may be misleading in genotypes which accumulate high amounts of Al

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01336.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYGrowth and photosynthetic performance were assessed for the Finnish wheatTriticum aestivumL. var. APU under a cool (13/10°C day/night) and a warm (30/25°C day/night) regime. Plants exhibited a certain degree of acclimation to warm growth conditions. This acclimation appeared to involve enhanced performance of both photosystem II and whole‐chain electron transport. Enhanced thermal stability of photophosphorylation was also observed in warm‐grown p

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01337.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYThis paper presents basic data regarding the seed heteromorphism in a population of the short‐lived perennial halophyteSpergularia media. Essentially two seed types exist, unwinged and winged seeds. The variation in seed size and the existence and the extent of seed wings was investigated in a population from the western coast of Sweden. Seeds were collected both directly from plants growing under natural conditions, and from plants developed out of soil samples brought into a greenhouse after the seed set in the autumn. The seed size varied considerably and the width of the seed wing was positively related to the length of the seed body, but in contrast to the situation in the closely related annualS. marina(where the winged seeds have appreciably larger seed bodies than the unwinged seeds), the average seed body length differed only marginally (but in the same direction) between the seed types inS. media. Most of the plants produced either exclusively winged or unwinged seeds, but still 45%Fieldor 10%Greenhouseof the plants were found to produce capsules with heteromorphic seeds (strongly dominated by the winged seed type). The spatial distribution of the different seed types in an environmental gradient comprising surrounding vegetation of sparse, intermediate and dense covering was also investigated. Seed capsules containing only winged seeds were more common in the dense vegetation. Inversely, capsules with unwinged seed contents were more frequently encountered in open areas. No such relation was found between the vegetation density and the proportion of capsules with heteromorphic seeds. A hypothesis is presented saying that the production of two seed types inS. mediais dictated by the pressure for greater efficacy in seed dispersal in combination with differential survival and reproduction of the two different seed morph

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01338.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYField experiments were designed to determine the timing of germination and the character of the seedbank in relation to the field occurrence of threeRumexspecies, which are distributed in a gradient of intensity and predictability of floods in river flood‐plains.Rumex acetosais characterized by early autumn germination, a transient type of seedbank, flood‐intolerant achenes and a lack of multiple post‐flood germination cohorts. These traits fit well into the habitat ofR. acetosain river flood‐plains: rarely flooded grasslands with a high level of competitive interactions. Both wetland species,R. crispusandR. palustris, are characterized by late spring germination, a persistent seedbank, flood‐tolerant achenes and multiple post‐flood germination cohorts. These traits fit into the habitats of both species which are characterized by harsh predictable winter floods and erratic catastrophic summer floods. Timing of germination and seedbank characteristics are important life‐history traits, at least partly explaining the distribution ofRumexspecies in flood‐dominated riv

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01339.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYThe germination responses ofRumex acetosa, R. crispusandR. palustriswere studied in relation to perianth‐imposed primary dormancy, the temperature and light control of germination and response to hypoxia. The perianth‐imposed primary dormancy inR. crispusandR. palustrisis related to light filtering through the perianth and/or inhibited water uptake due to a water repulsive layer around the perianths.Rumex acetosais able to germinate at a constant rate over a wide range of temperatures, whereas both the other species are characterized by fast and maximal germination at regimes with higher upper temperatures; in this senseR. palustriswas the most extreme species. InR. acetosa, germination in light and dark is independent of diurnal fluctuating temperatures. Dark germination inR. crispusis stimulated by alternating temperatures.Rumex palustrisneeds both light and fluctuating temperatures to induce germination. Differences in germination behaviour in relation to light and temperature are discussed in relation to the phytochrome regulation ofRumexgermination. In contrast toR. acetosa, imbibed achenes of bothR. crispusandR. palustrisare able to survive a prolonged hypoxic incubation. The results are discussed in relation to the distribution of the threeRumexspecies in a flooding gradient of a river a

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01340.x

年代:1992

数据来源: WILEY

摘要:

SUMMARYA stand of the seagrassHalophila stipulacea(Forssk.) Aschers. has been discovered at the Ionian Island of Kefallinia. Detached floating plants have been observed in various harbours on Kefallinia and Ithaki, indicating a further range extension in the Mediterranean.

ISSN:0044-5983    

DOI:10.1111/j.1438-8677.1992.tb01341.x

年代:1992

数据来源: WILEY