Random amplified polymorphic DNAs (RAPDs) and inter-simple sequence repeats (ISSRs) markers were used to analyze genetic structure of six populations of invasive plant Eichhornia crassipes that were sampled from its introduced regions in Southern China. Using 25 RAPD primers and 18 ISSR primers, 172 RAPD bands and 145 ISSR bands were produced respectively. But no polymorphic band was detected either within population or among populations by both markers, indicating the genetic diversity of E. crassipes in Southern China is extremely low, and all populations most likely consist of the same genotype. This study suggested that some other adaptability related factors, other than the genetic diversity, are responsible to the E. crassipes rapid expansion in China.

Alternanthera philoxeroides (Mart.) Grisb was introduced into China in the 1930s, and today occurs in most regions of southern China. Techniques using random amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR) markers were applied to analyze genetic diversity of this invasive, weedy species. The fragments amplified by both 28 RAPD primers and 23 ISSR primers showed no polymorphic bands within and among the seven populations sampled. These results might be a consequence of the short introduction history in China and the clonal propagation of this aquatic plant. Although A. philoxeroides is widely distributed in China, the molecular data indicated its genetic diversity is extremely low, which implies that the low genetic diversity did not affect the success of its expansion in China. The rapid range expansion of A. philoxeroides is most likely the result of a massive clonal propagation since its introduction.

Background and Aims Seed coat morphology is known to be an excellent character for taxonomic and evolutionary studies, thus understanding its structure and development has been an important goal for biologists. Thisresearch aimed to identify the developmental differences of seed coats between amphidiploids and their putative parents in Brassica. Methods Scanning electron microscope (SEM) studies were carried out on six species (12 accessions), three amphidiploids and their three diploid parents. Key Results Twelve types of basic ornamentation patterns were recognized during the whole developmental process of the seed coat. Six types of seed coat patterns appeared in three accessions of Brassica rapa, five types in B. oleracea, B. nigra and B. carinata, seven types in B. napus, and eight types in B. juncea. There was less difference among seed coat patterns of the three accessions of B. rapa. The reticulate and blister types were two of the most common patterns during the development of seeds in the six species, the blister-pimple and the pimple-foveate patterns were characteristic of B. rapa, and the ruminate of B. oleracea and B. nigra. The development of seed coat pattern in amphidiploids varied complicatedly. Some accessions showed intermediate patterns between the two putative parents, while others resembled only one of the two parents. Conclusions The variation in the patterns of seed coat development could be used to provide a new and more effective way to analyse the close relationship among amphidiploids and their ancestral parents.

The distribution of Ca2+ in the anthers of wheat was observed using cytochemical method of potassium antimonite. At the later tetrad stage, Ubisch bodies carrying Ca2+ were observed on the inner surface of tapetum, in anther locule and on pollen surface. The Ubisch bodies contacted with pollen, and Ca2+ began to accumulate on pollen surface. At the uninucleate pollen stage, abundant Ubisch bodies were distributed in anther locule, and the amount of Ca2+ on pollen surface increased. At the mature pollen stage a large amount of Ca2+ ions were localized on the inner surface of tapetum, the surface of pollen and Ubisch bodies. In the pollen wall, Ca2+ precipitates arranged in radial lines. These results demonstrated that Ubisch bodies were involved in Ca2+transport from anther wall to pollen surface at some developmental stages of anther.

Potassium antimonate was used to locate loosely bound calcium in the pepper (Capsicum annuum) anther under normal and heat stress environments. In the microspore mother cell, a few calcium precipitates were deposited on the surface of the cell, a few in the cytoplasm and almost no precipitates were formed in the nucleus. After 12h at 40℃, antimonate calcium deposits increased in the cytoplasm and the nucleus and many emerged on the inner surface of the vacuole membrane. After 24h heat stress, some cells were partly deformed, numerous calcium precipitates appeared in the cytoplasm and deposited on the surface of the vacuole membrane and in the vacuoles. Compared to the pollen mother cell, there was a significant increase in calcium deposit quantities on the surface and in the cytoplasm of the tetraspore. By heat stressing for 24h, precipitates obviously increased in the cytoplasm and nucleus of the tetraspore in contrast to the control. In the microspore, many calcium precipitates were formed on the baculae, the inner surface of plasma membrane, vacuole membrane, but only a few in the cytoplasm and nucleus. After 12h heat exposure, precipitates on plasma membrane became abundant, a few in the cytoplasm and the peripheral nucleus, while no precipitates were seen on the vacuole membrane. As for the anthers exposed to 24h heat stress, precipitates increased on the inner surface of the plasma membrane, cytoplasm and nucleus. In mature pollen, there was a layer of calcium-induced precipitates on the pollen wall, but few in the cytoplasm and plasma membrane. No obvious calcium changes occurred on mature pollen after 12 or 24h heat exposure. The relationship between heat stress and calcium distribution was discussed.

Potamogeton erispus is a cosmopolitan aquatic species occurmlg in a wide range of climatic habitats. The effects of water depth, light availability, substrate type and simulated predation (by removing germinated sprouts) on truion germination of P. erispus were monitored from 1999 to 2000 under field conditions in Hubei province, China. The gemtination rate of the turions decreased at a mean rate 0.05m 1 per day with increasiilg water depth irrespective of lake. There were significant negative linear relationships between gemtination rate and water depth both of the same lake and across the lakes. Turion gemtination was iilhibited in the dark, but was little affected by types of substrate. Removing the gemtinated sprouts promoted germiilation of other dormant buds. Therefore, the potential to gemtinate further after sprout removal might be one mechunism by which 13 erispus can dominate habitats with predation pressme from herbivorous fishes. The results may be used to predict turion gemtination dynamics of P. erispus from water depth of lakes providing light attenuation does not change, and to construct a population model.