摘要:

Populations of each of the 11 species of the North American angiosperm genusPolygonella(Polygonaceae) were sampled for electrophoretically detectable allozyme diversity. In contrast to expectations based on similar surveys in many other vascular plant groups, the two most widespread species ofPolygonellashowed reduced within‐population gene diversity with respect to their narrowly endemic congeners. One possible explanation is that high levels of selfing in the widespread species have led to reduced population‐level diversity. An alternative explanation is that large‐scale migration during Pleistocene glaciations removed much of the diversity of these more northerly distributed species, while the endemics, several of which inhabit known Pleistocene refugia, were able to maintain higher levels of diversity because of population stability during the glacial cycles. If the latter explanation is correct, an important implication for conservation is that, for many genera in eastern North America, the species richest in gene diversity may be those most in danger of extirpation in the next decade, namely those species endemic to Pleistocene refugia such as the Lake Wales Ridge.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11483.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The development and physiological consequences of ozone‐induced visible injury was investigated in native populations of Jeffrey pine (Pinus jeffreyi) that were exposed to chronic levels of anthropogenic ozone. Stand structure analyses demonstrated that the expression of visible ozone injury symptoms within self‐regenerating populations of Jeffrey pine was highly variable. Of the 975 trees surveyed, 90% exhibited some degree of visible injury and 10% were classified as resistant to ozone. Needles of the most sensitive trees developed a chlorotic mottle characteristic of ozone injury 1 year after their initiation and prematurely abscised in their third year (normal needle retention is 5–6 years). Average needle retention was not different between diameter size categories but was the most variable within the smallest size category and the least variable in the largest size category. Gas exchange measurements indicated a negative correlation between photosynthetic rate and needle surface area covered by chlorotic mottle. Chlorophyll fluorescence kinetics of the current‐year needles did not differ between symptomatic and asymptomatic trees but did differ between the oldest needles, suggesting an uncontrolled physiological decline in needles about to abscise in sensitive trees. The high degree of variability of ozone‐induced visible injury coupled with the reduction of physiological capacity associated with visible injury suggest that mixed conifer forests growing in polluted regions could potentially undergo shifts in community structure if sensitive Jeffrey pine individuals were to experience differential mortality as a result of ozone exposure. Intraspecific variation in ozone sensitivity may potentially lead to increased population tolerance to oxidative air pollutants, but long‐term population analyses will be required to address genetic changes in response to ozone stress.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11484.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Morphological and anatomical changes for first‐order daughter cladodes (flattened stem segments) of a prickly pear cactus,Opuntia ficus‐indica, were monitored to determine the effects of a doubled atmospheric CO2concentration on their development and mature form. For daughter cladodes developing in controlled environment chambers for 60 d, maximal elongation rates were similar under a photosynthetic photon flux density (PPFD) of 6 mol m−2d−1and a CO2concentration of 370μl liter−1, an increased PPFD (10 mol m−2d−1), and an increased PPFD and a doubled CO2concentration. These maximal rates, however, occurred at 20, 15, and 12 d, respectively. The maximal relative growth rate under the doubled CO2concentration was about twice that under the other conditions. For cladodes at 60 d as well as after 4 and 16 mo in open‐top chambers, doubling the CO2concentration had no effect on final length or width. At 4 mo, cladodes under doubled C02were 27% thicker, perhaps allowing the earlier production of second‐order daughter cladodes. The chlorenchyma was then 31% thicker and composed of longer cells. At 16 mo, the difference in cladode thickness diminished, but the chlorenchyma remained thicker under doubled CO2, which may contribute to greater net CO2uptake forO. ficus‐indicaunder elevated CO2concentrations. Two other persistent differences were a 20% lower stomatal frequency and a 30% thicker cuticle with more epicuticular wax for cladodes under doubled CO2, both of which may help reduce transpirational water loss.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11485.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Ontogenetic color changes in fully turgid flowers are widespread throughout the angiosperms, and in many cases are known to provide signals for pollinators. A broad survey of flowering plants demonstrates that such color changes appear in at least 77 diverse families. Color‐changing taxa occur commonly within what are considered derived lineages, and only rarely in early or primitive groups. The pattern of distribution of floral color change across orders, families, genera, and species demonstrates that the occurrence of the phenomenon within a group is not simply a result of phylogenetic history. Color changes can affect the whole flower or they can be localized, affecting at least nine floral parts or regions. The scale of color change (localized or whole‐flower) is broadly correlated with the type of pollinator that characteristically visits the plant. Color changes can come about through seven distinct physiological mechanisms, involving anthocyanins, carotenoids, and betalains. Color changes due to appearance of anthocyanin are the most common, occurring in 68 families. Floral color change has clearly evolved independently many times, most likely in response to selection by visually oriented pollinators, and reflects a widespread functional convergence within the angiosperms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11486.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The ultrastructure of the embryo sac, nucellus, and parts of the micropyle ofLilium longiflorumwere studied both before and after pollen tube penetration to examine the interactions between ovule and pollen tube, using transmission electron microscopy and light microscopy. Before pollen tube penetration the egg cell and two synergids are similar. No filiform apparatus was detected and no synergid degeneration occurs prior to pollen tube penetration. The polar nuclei do not fuse until fertilization. No differences in embryo sac ultrastructure were detected between pollinated ovules unpenetrated by pollen tubes and unpollinated flowers of a comparable age. Shortly after the discharge of the pollen tube two enucleated cytoplasmic bodies with different ribosome densities were observed in the degenerated cytoplasm. These structures border both on the central cell and the egg cell as well as each other and are interpreted as remains of sperm cytoplasm after transmission of sperm nuclei. In the central cell both the sperm nucleus and the polar nuclei are associated with endoplasmic reticulum (ER). ER is thought to be a transport mechanism to achieve contact between the haploid polar nuclei and the sperm nucleus. In the egg cell sperm nucleus alignment is not visibly achieved by ER. The persistent cells of the egg apparatus and the central cell appear to become more metabolically active after pollen tube penetration. Pollen tube penetration already occurs despite the absence of a filiform apparatus and a low level of differences between the cells of the egg apparatus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11487.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Nectar is the most common floral reward that plants produce to attract pollinators. To determine the effect of nectar production on hawkmoth behavior, pollen movement, and reproductive success inMirabilis multiflora, I manipulated nectar volumes and observed the subsequent foraging behavior of the hawkmothHyles lineataand the resulting pollen movement patterns. Individual hawkmoths visited significantly more flowers on plants with more nectar. The increase in flower visits significantly increased pollen deposition on stigmas and pollen removal from anthers when nectar volume was raised to twice the highest level found in nature. As hawkmoths visited flowers consecutively on a plant, the proportion of self pollen deposited on stigmas increased significantly and rapidly. Based on simulated hawkmoth visits, seed set was significantly reduced for flowers later in a visit sequence. A simple model combining these results predicts that the form of selection on nectar production varies depending on pollinator abundance. Using a multiple regression analysis a nearly significant (P<0.08) effect of stabilizing selection was detected during a single season as predicted by the model for the prevailing hawkmoth abundance. Although increased nectar production may indirectly affect plant fitness by reducing resources available for other plant functions, the direct effect of high nectar production on pollinator behavior and self pollination may generally limit floral nectar production.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11488.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The ultrastructure, morphology, and histology of zygotic embryogenesis in pearl millet (Pennisetum glaucum) were examined using light and electron microscopic techniques. Embryogenesis was initially characterized by the presence of a vacuolated egg cell and zygote. The increased presence of Golgi bodies in the zygote suggested it was metabolically more active than the egg cell. The first zygotic division resulted in a densely cytoplasmic apical cell and a highly vacuolated basal cell. The club‐shaped proembryo displayed a large amount of endoplasmic reticulum (ER) and ribosomes, very few lipids, and a continuous gradient of vacuoles from the highly vacuolated basal suspensor cells to the densely cytoplasmic apical cells. The embryo had well‐defined parts by 8 days after pollination, including shoot and root meristems, coleoptile, scutellum, provascular system, and the first leaf primordium. Large increases in ER, lipids, starch, and vacuoles occurred in the scutellum during the maturation of the embryo, except in the provascular cells. Throughout zygotic embryogenesis, embryo cells were connected by plasmodesmata except where intercellular spaces occurred. Ultrastructural, morphological, and histological observations of zygotic embryogenesis in pearl millet are in agreement with previous reports for other grass species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11489.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

In contrast to higher plants, the algaCharahas rhizoids with single membrane‐bound compartments that function as statoliths in gravity perception. Previous work has demonstrated that these statoliths contain barium sulfate crystals. In this study, we show that statoliths inChararhizoids react with a Coomassie Brilliant Blue cytochemical stain for proteins. While statoliths did not react with silver methenamine carbohydrate cytochemistry, the monoclonal antibody CCRC‐M2, which is against a carbohydrate (sycamore‐maple rhamnogalacturonan I), labeled the statolith compartment. These results demonstrate that in addition to barium sulfate, statoliths inChararhizoids have an organic matrix that consists of protein and carbohydrate moieties. Since the statoliths were silver methenamine negative, the carbohydrate in this compartment could be a 3‐linked polysaccharide. CCRC‐M2 also labeled Golgi cistemae, Golgi‐associated vesicles, apical vesicles, and cell walls in the rhizoids. The specificity of CCRC‐M2 immunolabeling was verified by several control experiments, including the demonstration that labeling was abolished when the antibody was preabsorbed with its antigen. Since in this and a previous study (John Z. Kiss and L. Andrew Staehelin,American Journal of Botany80: 273–282, 1993) antibodies against higher plant carbohydrates crossreacted with cell walls ofCharain a specific manner, Characean algae may be a useful model system in biochemical and molecular studies of cell walls.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11490.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The intra‐ and interspecific relations between the size and number of pollen grains were examined for 21 species of papilionaceous legumes to test for the trade‐off expected from the subdivision of limited resources. We observed a tradeoff between pollen grain diameter and the number of grains produced per flower within 17 of the 21 species examined. For 12 of these species, the observed partial regression coefficient for In (pollen grain diameter) equaled ‐3, as expected. The remaining five species exhibited more negative partial regression coefficients than expected. Relations between pollen grain size and number that are more negative than expected may result from a decelerating relation between pollen grain size and the resource investment per grain. Flower production significantly influenced pollen production for only eight species so that pollen production seems to be determined primarily on a per flower basis. Interspecifically, pollen size also varied inversely with pollen number for the 21 species even after the effect of phylogenetic relatedness was removed. Pollen size varies relatively little compared to the number of pollen grains produced per flower and therefore may be the primary target of natural selection. The presence of a trade‐off in pollen production probably constrains the evolutionary options by which flowering plants can maximize male success.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11491.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Chloroplast DNA (cpDNA) restriction site variation was examined in 32 species, representing five subgenera, ofBromus(Poaceae). Thirty‐seven phylogenetically informative restriction sites were detected. Cladistic analysis of the restriction site data produced a single most‐parsimonious tree of 50 steps. The cladogram indicated two major clades within the genus. One clade includedB. triniiof subgenusNeobromusand species of subgenusCeratochloa.The other was composed of subgeneraFestucaria, Stenobromus, andBromus.Within the second clade, species of subgenusFestucariaappeared in three lineages. The second clade also contained an assemblage of species belonging to subgeneraStenobromusandBromusin a separate lineage. There was very little resolution of relationships in this assemblage since several species appeared individually in separate lineages. The cpDNA phylogenetic hypothesis did not separate species of subgeneraStenobromusandBromusinto well‐defined clades as circumscribed by morphology and cytogenetics. The cpDNA tree is in agreement with the phylogenetic scheme based on traditional data in that: 1) subgeneraNeobromusandCeratochloawere the first to diverge, whileBromusandStenobromusdiverged later; 2) within the genusBromusspecies with small chromosomes are ancestral; and 3) subgeneraBromusandStenobromusprobably originated from similar ancestors asFestucaria.The tree based on cpDNA data does not support that: 1) subgeneraNeobromusandCeratochloadid not have a common origin; 2) subgenusFestucariais monophyletic; and 3) subgeneraStenobromusandBromusare distinct entities. The mean nucleotide sequence divergence values between pairs of subgenera ranged fromp= 0.0 to 0.9. These values suggest that cpDNA evolution inBromusis slow.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11492.x

出版商:Wiley    

年代:1995

数据来源: WILEY