ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11525.x

出版商:Wiley    

年代:1995

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11526.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Pollen allelopathy occurs when pollen toxins inhibit sexual reproduction in heterospecifics. To quantify pollen allelopathic effects in vitro, pollen ofHieracium aurantiacum, H. floribundum, andH. pratensewas extracted with double distilled water into concentrations of 0 (control), 0.1, 1, 3, 5, 10, and 25 pollen grains/μl. A subset of these extracts was partitioned by ion‐exchange chromatography into acidic, basic, and neutral fractions. Pollen from six sympatric species of Fabaceae (Lotus corniculatus, Medicago sativa, Trifolium hybridum, T. pratense, T. repens, Vicia cracca) and the species ofHieraciumwas germinated on agar media containing different extract concentrations. As extract concentrations from intact pollen or from acidic fractions increased, mean percent germination of pollen of all Fabaceae decreased nonlinearly. Extract concentrations of 0.1 grains/μl and above inhibited pollen germination in the Fabaceae. In no case was anyHieraciumspecies affected, i.e., there was no autotoxicity. Similar results were obtained using plants from nine populations ofH. floribundumandH. pratenseacross eastern Canada. Observation of floral visitors indicated that there were relatively few movements betweenHieraciumand the Fabaceae (about 15% of total visits). Hence there is limited opportunity for heterospecific pollen transfer. This was consistent with censuses of stigma, i.e., few pollen grains ofHieraciumwere found on stigma of the Fabaceae. Thus, pollen allelopathy inHieraciumis unlikely to affect reproductive success in these six species of Fabaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15646.x

出版商:Wiley    

年代:1995

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11527.x

出版商:Wiley    

年代:1995

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11528.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The influence of enantiostyly (reciprocal segregation of anthers and stigmas to different sides of the flower) on outcrossing rate was examined inChamaecrista fasciculata(Leguminosae). I hypothesized that enantiostyly has not evolved to increase the female component of outcrossing and actually acts to increase the selling rate through geitonogamy. To quantify the role of enantiostyly to outcrossing, plants of known isozyme genotype were manipulated to be either completely left‐ or right‐styled (nonenantiostylous) or to have equal numbers of left‐ and right‐styled flowers (enantiostylous). Flower number was varied to quantify any interaction between floral display size and enantiostyly on outcrossing rate. These “target” plants were surrounded by unmanipulated plants homozygous for the alternative allele. Outcrossing rates of the target plants were determined by scoring the presence or absence of heterozygotes. The contribution of enantiostyly to geitonogamy may be reduced if pollinators discriminate among the floral types. Thus, observations of pollinator movement between flowers on the same plant were made to determine if pollinators discriminate between the floral types. Although pollinators moved randomly between flower types, outcrossing rate was only marginally effected by the presence of enantiostyly. Enantiostylous plants outcrossed at a slightly lower rate than nonenantiostylous plants only when the opportunity for geitonogamy was great. These results suggest that the contribution of enantiostyly to selling is minimal.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15647.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Most species ofDalechampiahave expanded stigmatic surfaces that extend from the stylar tip part way down the sides of the elongated styles. Pollen grains landing at the stylar tip grow tubes directly down the style to the ovary. Pollen grains landing on the lateral stigmatic surfaces, however, exhibit indirect pollen‐tube growth: the tubes grow first to the stylar tip, bend 180°, and then grow to the ovary. Indirect pollen‐tube growth appears to be reproductively important: more than half the arriving pollen lands on the lateral stigmatic surfaces, and virtually all of these grains produce tubes that grow indirectly to the ovary; pollen on the lateral surface fertilizes seeds about as effectively as pollen at the tip (with direct tube growth). Indirect pollen‐tube growth may be the result of a correlated response to selection for expanded stigmatic surfaces inDalechampia, or it may be an adaptation to increase the intensity of pollen competition.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15648.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

TheTripsacumagamic complex (x= 18) will provide valuable characters for maize breeding, provided that apomixis can be manipulated. Apomixis inTripsacumwas first reported 40 years ago, but its prevalence in the genus has not been established. Reproductive development was determined for eight Mexican and two South AmericanTripsacumspecies by microscopic analysis of ovaries cleared in a benzyl benzoate‐dibutyl phthalate solution using interference contrast optics. The occurrence and distribution of callose deposition during megasporogenesis were determined by fluorescence microscopy of ovaries optically cleared in an aqueous sucrose solution containing aniline blue. Diploid genotypes were sexual. Polyploid forms reproduced apomictically following the Antennaria type (complete meiosis abortion) of diplospory. The Taraxacum type (unreduced megaspore production through meiotic restitution nuclei) of diplospory also occurred but rarely. The walls of diplosporic megasporocytes lacked callose whereas the walls of sexual megasporocytes contained a normal complement of callose. The absence of callose suggests that the diplosporic forms of reproduction result from mutations affecting the normal meiotic process. Apomixis in theTripsacumgenus is facultative, and the production of new polyploid genotypes through genetic exchanges involving both apomictic and sexual genotypes is possible.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15649.x

出版商:Wiley    

年代:1995

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb11529.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Argentine popcorn is an exotic race considered by some to be similar to the earliest cultivated maize. We used scanning electron microscopy to examine inflorescence development in both the tassel and ear. In our material, and under our conditions, both two‐ranked central tassel spikes and two‐ranked ears were observed as well as more typical four‐ranked structures. Subsequent development of spikelets and florets was similar to that observed in other varieties of maize and in their close relatives—the teosintes. We suggest that the switch from two‐ranked to four‐ranked inflorescences (a key trait difference between teosinte and maize) may be due to a change in developmental timing allowing an additional meristem bifurcation of axillary branch primordia prior to the initiation of spikelet pair primordia.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb15650.x

出版商:Wiley    

年代:1995

数据来源: WILEY