Regulation of seed number and female incitation of mate competition by a pH-dependent proteinaceous inhibitor of pollen grain germination in Leucaena leucocephala

Summary Leucaena leucocephala generally produces pods with more than 7–9 seeds. This is regulated by the stigmatic inhibition of pollen grain germination when the pollen grains are less than a critical number in the stigma. This number-dependent inhibition of pollen grain germination is effected by a pH-dependent proteinaceous inhibitor active at the stigmatic pH. Only when the pollen grains in the stigma exceed the critical number, they inactivate the inhibitor by collectively raising the stigmatic pH and thus overcoming the inhibition. The adaptive significance of such pre-fertilization mechanism for the female in inciting mate competition among the pollen grains is discussed. The evolution of en masse pollen grain dispersal units is explained as a sexual selection strategy by males in response to such stigmatic inhibition by females.     

Antibodies to pollen exines

A polyclonal antiserum and monoclonal antibodies have been prepared to purified pollen exines of Calocedrus decurrens Florin. The location of the antigen is in the exine, as shown by light-and electron-microscopic immunocytochemistry. The greatest reduction in antibody binding follows treatment of the exine with chemicals known to alter sporopollenin. These results provide evidence that sporopollenin is antigenic. Exines of ten species of gymnosperms and angiosperms also bound the polyclonal antiserum, indicating similarity of sporopollenin structure.     

Effects of Alternaria alternata f.sp. lycopersici toxins on pollen

Summary Effects of the phytotoxic compounds (AAL-toxins) isolated from cell-free culture filtrates of Alternaria alternata f.sp. lycopersici on in vitro pollen development were studied. AAL-toxins inhibited both germination and tube growth of pollen from several Lycopersicon genotypes. Pollen from susceptible genotypes, however, was more sensitive for AAL-toxins than pollen from resistant plants, while pollen of species not belonging to the host range of the fungus was not significantly affected by the tested toxin concentrations. AAL-toxins elicit symptoms in detached leaf bioassays indistinguishable from those observed on leaves of fungal infected tomato plants, and toxins play a major role in the pathogenesis. Apparently, pathogenesis-related processes and mechanisms involved in disease resistance are expressed in both vegetative and generative tissues. This overlap in gene expression between the sporophytic and gametophytic level of a plant may be advantageously utilized in plant breeding programmes. Pollen may be used to distinguish susceptible and resistant plants and to select for resistances and tolerances against phytotoxins and other selective agents.     

诱导小麦-天兰偃麦草-黑麦三属杂种花粉植株的研究

以法国六倍体小黑麦为母本,分别与普通小麦(Triticum aestivum)和天兰偃麦草(Elytrigia intermedia of Agropyron glaucum)的杂交后代中的中间类型3号和5号杂交。由此获得的三属杂种F_1性状介于亲本之间,兼有三属亲本类型的特征,呈中间类型。用马铃薯-Ⅱ培养基培养三属杂种F_1的花药,诱导花粉愈伤组织。将所获得的愈伤组织转入190-2培养基进行分化,已成功地诱导出一批三属间杂种花粉植株,并用Giemsa显带技术鉴定花粉植株的染色体组组成。     

Attempts to transform Zea mays via pollen grains

Summary An attempt was made to transfer two sorts of DNA into maize via pollen grains. Controls for both pollen quality and DNA behaviour during the transformation experiments were included. When genomic DNA was used, no transformants were observed among the 1805 seeds screened. With plasmid DNA (harbouring the gene expressing kanamycin resistance in plant cells), three plants with kanamycin resistance were observed among the 1723 seeds screened, although no molecular evidence of transformation was obtained. Experiments indicated that under the conditions used, DNA was being degraded by both pollen and stigma nucleases. Consequently, we attempted to determine protocols which would inhibit these nuclease activities in order to preserve DNA integrity during transformation experiments, thus allowing fertilization. We found that a classic germination medium supplemented by 300 or 600 mM KNO₃, or 20% PEG₁₅₅₀ satisfied all these conditions.Abbreviations BK Brewbaker and Kwack medium - BKS15 Brewbaker and Kwack medium containing 15% (w/v) sucrose - EDTA ethyldiaminetetraacetic acid - FCR fluorochromatic reaction - FP fertilization percentage - PEG polyethylene-glycol     

The structure and cytochemistry of the pistil of Hypericum calycinum: the style

Summary A typical style of Hypericum calycinum is solid with a core of transmitting tissue traversing the whole length of the style. This transmitting tissue consists of loosely arranged cells and large intercellular spaces filled with a secretion product. The secretion product is rich in lipids, but poor in proteins and polysaccharides. The intercellular spaces of the transmitting tissue originate partly by a separation of cells as a result of the decomposition of the middle lamella and partly by degeneration of some of the cells of the transmitting tissue. H. calycinum is self-compatible. Both self- and cross-pollinations result in profuse pollen germination on the stigma and pollen tube growth through the style. The data on Hypericum is discussed in relation to information available on other solidstyled systems.     

Endoparasitic flies,pollen-collection by bumblebees and a potential host-parasite conflict

Summary Conopid flies (Conopidae, Diptera) are common larval parasites of bumblebees. The larva develops inside the abdomen of workers, queens and males. Development is completed within 10–12 days after oviposition when the host is killed and the parasite pupates in situ. Development results in parasitised bees becoming unable to carry large loads of nectar, as the conopid larvae reside where the honey crop is normally located. Furthermore, an addition to the bee's unloaden body mass is likely (average larval weight reached at pupation by the common parasite species Sicus ferrugineus: ±SD 36.3±12.3 mg, n=59; by Physocephala rufipes: 55.8±16.9 mg, n=108). We here asked whether the propensity of workers of the bumblebee Bombus pascuorum to collect nectar rather than pollen is related to the presence of conopid larvae. For samples of bees (n=2254 workers) collected over 3 years of field studies in northwestern Switzerland, there was no difference in the frequency of bees caught as pollen collectors among parasitised (38.1% of cases, n=210) as compared to non-parastised bees (43.9%, n=360) ( ²=1.83, n.s.). However, compared to the non-parasitised bees (n=360), those hosts containing a third (last) instar larva (n=9) were less likely to collect pollen than expected by chance ²=6.91, P=0.003. Similarly, hosts with short survival time between capture and being killed by the developing larva (which hence must have harboured a late instar parasite at time of capture) were less likely to collect pollen (8%, n=25) than those found not parasitised (37.6%, n=891 ²=9.16, P<0.001). Late instar larvae grow so big that they fill the entire abdomen. Although there was also a tendency for presumably older bees to collect less pollen, this is unlikely to explain the observations. We also discuss whether these changes in foraging behaviour of bumblebees may reflect a host-parasite conflict over the type of resource to be collected.     

Effect of electrical fields and external ionic currents on pollen-tube orientation

Summary Agapanthus umbelatus pollen tubes (PTs) display a number of different growth patterns when germinated in an electric field of 750 mV· mm^–1. When pollen is germinated near the cathode (82.44% of orientation to the cathode side) or near the anode (55.35% of orientation to the anode), growth is oriented parallel to the applied field but when germinated at an intermediate position, there is random growth. An increase and decrease in the orientation rates as well as reversion of the polarized growth were observed when the growth conditions were systematically altered. These findings reflect the influence of different ionic currents present in the germination medium. These ionic currents induce the formation of ionic gradients, which were monitored by ion-HPLC. The individual omission of Ca²⁺, K⁺, Mg²⁺ and Cl^– suppresses or alters the oriented growth pattern. The presence of ionic gradients is not by itself suficient to trigger the polarization of tube growth as the presence of an electric field which drives the ionic currents is essential for this to occur.Abbreviations PT Pollen tube - DNS 3,5-dinitro salycilic acid; - TP transient polarization - HPLC high precision liquid chroma tography - DC direct current