摘要:

Freeze‐fracture electron microscopy was used to investigate intramembranous particle (IMP) densities and particle distributions in the plasma membrane and tonoplast of the cells of secreting and nonsecreting leaves ofAvicennia germinans(L.) Steam. Intramembranous particle densities of the protoplasmic (P) and exoplasmic (E) face of the plasma membrane and tonoplast were significantly higher in hypodermal cells of secreting leaves than of nonsecreting leaves. In contrast, no significant differences in the frequency of intramembranous particles were found in any membrane faces of secreting or nonsecreting mesophyll cells. However, particle densities were higher in the plasma membrane and tonoplast of the mesophyll cells, compared to the hypodermal cells, with the exception of the P‐face of hypodermal plasma membranes of secreting tissue, which had the highest particle density measured. Particle distributions were dispersed and no discernible patterns such as paracrystalline arrays or other multi‐IMP structures were observed. Results support the hypothesis that secretion is coupled to changes in membrane ultrastructure, and the possibility that salt secretion is an active process driven by integral membrane proteins such as the H+/ATPase. Additionally, the hypodermal cells of the leaf may function as storage reservoirs for salt as well as water, suggesting a regulatory role in salt secretion.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15661.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Sporophytes of some epiphytic species in the fern genusPyrrosiaexhibit Crassulacean acid metabolism (CAM), generally considered to be a derived physiological response to xeric habitats. Because these species alternate between independent sporophytic and gametophytic generations yet only the sporophyte has been characterized physiologically, experiments were conducted to determine the photosynthetic pathways present in mature sporophytes, immature sporophytes, and gametophytes ofPyrrosia longifolia.Diurnal CO2exchange and malic acid fluctuations demonstrated that although the mature sporophytes exhibited CAM, only C3photosynthesis occurred in the gametophytes and young sporophytes. Consideration of the above results and those from previous studies, as well as the life cycle of ferns, indicates that the induction of CAM probably occurs at a certain developmental stage of the sporophyte and/or following exposure to stress. Elucidation of the precise mechanisms underlying this C3‐CAM transition awaits further research.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15662.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Tropical regions currently receive the highest levels of global solar ultraviolet‐B radiation (UV‐B, 280–320 nm) even without ozone depletion. The influence of natural, present‐day UV‐B irradiance in the tropics was examined for five tropical species including three native rain forest tree species (Cecropia obtusifolia, Tetragastris panamensis, Calophyilum longifolium) and two economically important species(Swietenia macrophylla, Manihot esculenta). Solar UV‐B radiation conditions in a small clearing on Barro Colorado Island, Panama (9° N), were obtained using either a UV‐B‐excluding plastic film or a film that transmits most of the solar UV‐B. Significant differences between UV‐B‐excluded and near‐ambient UV‐B plants were often exhibited as increased foliar UV‐B absorbing compounds and, in several cases, as reduced plant height with exposure to solar UV‐B. Increases in leaf mass per area and reductions in leaf blade length under solar UV‐B occurred less frequently. Biomass and photosystem II function using chlorophyllafluorescence were generally unaffected. The results of this study provide evidence that tropical vegetation, including native rain forest species, responds to the present level of natural solar UV‐B radiation. This suggests that even minor ozone depletion in the tropics may have biological implications.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15663.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

This 2‐year field study examined stomatal conductance, photosynthesis, and biomass allocation ofLiquidambar styracifluasaplings in response to below‐ and aboveground competition with the vinesLonicera japonicaandParthenocissus quinquefolia.Vine competition did not affect stomatal conductance of the host trees. The leaf photosynthetic capacity and photosynthetic nitrogen‐use efficiency were significantly reduced by root competition with vines, either singly or in combination with aboveground competition, early in the second growing season. However, such differences disappeared by the end of the second growing season. Trees competing below ground with vines also had lower allocation to leaves compared with steins. Aboveground competition with vines resulted in reduced photosynthetic capacity per unit leaf area, but not per unit leaf weight, in trees. No correlation was found between single leaf photosynthetic capacity and tree growth. In contrast, a high positive correlation existed between allocation to leaves and diameter growth. Results from this study suggest that allocation patterns are more affected than leaf photosynthesis in trees competing with vines.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15664.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Hand pollinations are frequently used to assess the postpollination success of different donors. We present evidence that the method used for hand pollinations can alter pollen germination rates and paternity of the resulting seeds. Two commonly used methods for hand pollination experiments are mixed pollinations, where pollen from several donors is physically mixed together, and adjacent pollinations, where pollen from one donor is close to, but not in physical contact with, pollen from other donors. These methods offer differing opportunities for pollen interaction, and for females to choose among mates. We found that the success of pollen donors in multidonor pollinations varied with pollination method in unpredictable ways across maternal plants. Pollen germination was significantly lower in adjacent pollinations, perhaps explaining some of the effects of pollination method on paternity. These results may yield insights on the factors influencing pollen success, and indicate that hand pollination experiments should employ pollination methods that mimic as closely as possible the natural arrival of pollen in nature.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15665.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

We provide an estimate of genetic differentiation within and among 11 populations ofCordia alliodora, an economically important timber treeCordia alliodorais a widespread species that is distributed throughout Central and South America. Our survey of isozyme variation was conducted on material gathered for international provenance trials over approximately 1,000 km in Central America. Results from provenance trials indicate that there are significant differences between Atlantic and Pacific coast provenances for quantitative characters. Genetic data support some of these findings. Populations ofC. alliodorashow significant differences in allele frequency at various loci. Significant differences in multilocus allele frequencies occur at 13 of the 55 possible combinations. Eight of these 13 populations are situated on opposite coasts. This physical separation corresponds well with the results of provenance trials that indicate differentiation among the Atlantic and Pacific populations in quantitative morphological traits. We also found a significant negative correlation between levels of heterozygosity and the amount of rainfall, indicating that populations from the drier zone are genetically more heterogenous than populations from the wet zone. Our study indicates that in situ and ex situ conservation should accord high priority to the dry zone populations; furthermore, conservation of this widespread species would require preservation of multiple populations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15666.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

A multilocus mixed mating model was used to evaluate the mating system of a natural population ofCordia alliodora(Boraginaceae), a neotropical tree. The population was highly outcrossed (tm= 0.966 ± 0.027), in agreement with results from controlled crosses. Departures from the mixed mating model were evident, suggesting some nonrandom, correlated mating. Pollen pool heterogeneity and variation in estimates of individual outcrossing rates indicated that the population may be genetically substructured. Individual outcrossing rates obtained for the samples taken from within different parts of the same tree indicated reduced levels of outcrossing due to limited sampling of the pollen pool. The incompatibility mechanism inC. alliodora, combined with variation in flowering and stand density, appears to lead to both temporal and spatial substructuring of the population.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15667.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The utility of a) rare allozyme markers and b) paternity exclusion in estimating gene dispersal in tropical forest trees was demonstrated for a population ofCordia alliodora(R.&P.) Oken in Costa Rica. Based on the number of alleles in common, near neighbors were more highly related genetically than were more distant trees. The spatial clustering of relatives was within 50 m, coinciding to a large extent with the seed dispersal curve. Most pollen originated from within 75 m of the mother tree, although a low but substantial proportion of pollen movement was from as far as 280 m. Overall gene flow was extensive, with neighborhood areas as large as 7 ha. Neighborhood sizes at any moment in time and space were, however, relatively small, such that overall variation is maintained by continuous gene flow between neighborhoods. The results indicate that deforestation and fragmentation could curtail such gene flow leading to an erosion of genetic variation within fragments.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15668.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Three levels of soil nutrients and systematic removal of racemes and siliques, intended to reduce reproductive sink size, induced maternal effects in a genetically uniform, inbred accession ofArabidopsis thalianaecotype Col‐0. Soil nutrient levels but not trimming treatments caused significant differences in maternal plant weight and number of seeds per silique. Trimming and increased soil nutrient level resulted in larger seeds. Germination rates were significantly affected only by the trimming main effect, while there were no significant effects on germination percentage. At 14 and 19 d harvest dates, soil nutrient level treatments resulted in significant differences in offspring aerial biomass, but this effect was nonsignificant at 24, 29, and 34 d harvest dates. The effect of trimming on offspring aerial biomass was significant at all harvest dates. No significant soil nutrient level × trimming interaction was observed on any harvest date. Phenotypic correlations among aerial biomass at each harvest date and seed weight of the six offspring classes were highly significant. Analyses of variance for germination and biomass data adjusted for seed weight showed no significant differences due to soil nutrient level, trimming, or their interaction, indicating that maternal effects influencing these variables were determined by seed weight. Relative growth rates were estimated from changes in biomass over time. The negative correlation between initial relative growth rate and rate of change of the relative growth rate was highly significant(R= ‐0.99; P<0.01).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15669.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The aim of this study was to determine whether the fungicide Benlate 50 DF has adverse effects on the microtubules of cucumber root tip cells and on growth of the young seedlings. Germinating cucumber seeds and young seedlings were exposed to six concentrations of Benlate ranging from 1 mg/liter to 10 g/liter. Although seed germination was not affected by Benlate, seedling growth, especially number and length of branch roots, was reduced in proportion to the concentration of Benlate and length of treatment. Significantly lower mitotic indices were obtained from root tips exposed to 0.1, 0.6, 1, or 10 g/liter of Benlate. By means of immunofluorescence microscopy, the major microtubule arrays of root tip cells exposed to Benlate were compared and contrasted to those of controls. A few abnormalities in microtubule arrays were found at or after cytokinesis, and were of two types: 1) persistence of phragmoplast microtubules; and 2) presence of an array of microtubules between two recently divided daughter nuclei in the plane that would normally be occupied by the new cell wall. These abnormalities are somewhat similar to those induced by caffeine, and, as with caffeine treatment, possibly reflect impaired or/and incomplete cytokinesis that results in production of binucleate cells. A few binucleate cells were observed in root tips exposed to 10 g/liter of Benlate.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15670.x

出版商:Wiley    

年代:1995

数据来源: WILEY