粳稻品种幼苗耐冷性比较研究

利用人工模拟低温胁迫的方法,研究了３个日本粳稻品种日本晴、金南风和福光以及２个台湾粳稻品种台竹１５７、加南２０的苗期耐冷性,并以当地推广高产籼稻品种特三矮２号作对照。从对株高、主茎叶片数、地上部干物重、死苗率等形态性状的调查和叶绿素含量、电解质外渗率等生理性状测定的结果显示,日本晴、金南风、福光和台竹１５７苗期的耐冷性较强,加南２０的耐冷性较弱,但比特三矮２号的耐冷性略强。这为防止早稻烂秧死苗而开     

DOES COLCHICINE AFFECT AGGREGATION OF NORMAL AND TRANSFORMED BHK CELLS DIFFERENTLY?

The effect of colchicine and vinblastine on cell aggregation was studied, using BHK cells and their transformed derivatives (pyBHK cells). When cells were dissociated with EDTA and the assay was made in a Ca²⁺-containing medium, the aggregation of transformed cells was prevented by colchicine and vinblastine, whereas the aggregation of normal cells was unaffected. When a Ca²⁺-free medium was used for aggregation, neither type of cell was influenced by these drugs. BHK and pyBHK cells, dissociated by trypsin in the presence of Ca²⁺, can aggregate only in the Ca²⁺-containing medium and the aggregation of both cell types was equally prevented by colchicine and vinblastine. Based on these results, it was concluded that colchicine and vinblastine inhibited the Ca²⁺-dependent mechanism of cell adhesion, but not the Ca²⁺-independent one which occurs in the Ca²⁺-free aggregation medium.     

Biochemical and egg size evolution of freshwater fishes in the Rhinogobius brunneus complex (Pisces, Gobiidae) in Okinawa, Japan

Many colour morphs have been recognized in the Rhinogobius brunneus complex. A recent electrophoretic study has revealed that some of the colour morphs are well differentiated from each other genetically. In Okinawa, egg-size and life-history variation has been found in addition to the colour variation in this species complex. To clarify the nature of this life-history variation, gobies of a fluviatile morph with large eggs as well as three other amphidromous morphs with small eggs, inhabiting a single stream sympatrically in Okinawa, were analysed by electrophoresis and the females were also used for comparison of egg and clutch sizes. Electrophoretic data for 34 loci showed that each morph was separated by a fixed-allele difference for at least one locus, indicating that the four morphs which occurred sympatrically are reproductively isolated from each other. However, Nei's genetic distance between the fluviatile morph and one of the amphidromous morphs was much smaller (0.026) than distances among amphidromous gobies (0.323-0.480). Egg size of the former was by far the largest among the four. These results imply that speciation of the fluviatile morph accompanied by the egg-size increase has been completed rapidly without considerable genetic differentiation.     

Maternal information and localized maternal mRNAs in eggs and early embryos of the ascidian Halocynthia roretzi

Summary

The mosaic behavior of blastomeres isolated from ascidian embryos has been taken as evidence that localized ooplasmic factors (cytoplasmic determinants) specify tissue precursor cells during embryogenesis. Experiments involving the transfer of egg cytoplasm have revealed the presence and localization of various kinds of cytoplasmic determinants in eggs of Halocynthia roretzi. Three cell fates, epidermis, muscle and endoderm, are fixed by cytoplasmic determinants. The three kinds of tissue determinants move in different directions during ooplasmic segregation. Prior to the onset of the first cleavage the three kinds of determinants reside in egg regions that correspond to the future fate map of the embryo and then they are differentially partitioned into specific blastomeres. In addition to tissue-specific determinants, there is evidence suggesting that ascidian eggs contain localized cytoplasmic factors that are responsible for controlling the cleavage pattern and morphogenetic movements. Transplantation of posterior-vegetal egg cytoplasm to an anterior-vegetal position causes a reversal of the anterior-posterior polarity of the cleavage pattern. Localized cytoplasmic factors in the posterior-vegetal region are involved in the generation of a unique cleavage pattern. When vegetal pole cytoplasm is transplanted to the animal pole or equatorial position of the egg, ectopic gastrulation occurs at the site of transplantation. This finding supports the idea that vegetal pole cytoplasm specifies the site of gastrulation. Recently, we started a cDNA project to analyze maternal mRNAs. An arrayed cDNA library of fertilized eggs of H. roretzi was constructed, and more than 2000 clones have been partially sequenced so far. To estimate the proportion of the maternal mRNAs that are localized in the egg and embryo, 150 randomly selected clones were examined by in situ hybridization. We found eight mRNAs that are localized in the eight-cell embryo, of which three were localized to the myoplasm (a specific region of the egg cytoplasm that is partitioned into muscle-lineage blastomeres) of the egg, and then to the postplasm of cleavage-stage embryos. These results indicate that the proportion of localized messages is much higher than we expected. These localized maternal messages may be involved in the regulation of various developmental processes.