Exploring the effects of sowing date and ecological points on the yield of semi-winter wheat is of great significance.  This study aims to reveal the effects of sowing date and ecological points on the climate resources associated with wheat yield in the Rice–Wheat Rotation System.  With six sowing dates, the experiments were carried out in Donghai and Jianhu counties, Jiangsu Province, China using two semi-winter wheat varieties as the objects of this study.  The basic seedlings of the first sowing date (S1) were planted at 300×10⁴ plants ha⁻¹, which was increased by 10% for each of the delayed sowing dates (S2–S6).  The results showed that the delay of sowing date decreased the number of days, the effective accumulated temperature and the cumulative solar radiation in the whole growth period.  The yields of S1 were higher than those of S2 to S6 by 0.22–0.31, 0.5–0.78, 0.86–0.98, 1.14–1.38, and 1.36–1.59 t ha^–1, respectively.  For a given sowing date, the growth days increased as the ecological point was moved north, while both mean daily temperature and effective accumulative temperature decreased, but the cumulative radiation increased.  As a result, the yields at Donghai County were 0.01–0.39 t ha^–1 lower than those of Jianhu County for the six sowing dates.  The effective accumulative temperature and cumulative radiation both had significant positive correlations with yield.  The average temperature was significantly negatively correlated with the yield.  The decrease in grain yield was mainly due to the declines in grains per spike and 1 000-grain weight caused by the increase in the daily temperature and the decrease in the effective accumulative temperature.

Primary porcine tracheal epithelial cells (PTECs) are an appropriate model for studying the molecular mechanism of various porcine respiratory diseases, including swine-origin mycoplasmas, which are isolated from respiratory tract of pigs and mainly found on the mucosal surface surrounding swine trachea.  However, the short proliferation ability of primary PTECs greatly limits their lifespan.  In this study, primary PTECs were carefully isolated and cultured, and immortal PTECs were constructed by transfecting primary PTECs with the recombinant constructed plasmid pEGFP-hTERT containing human telomerase reverse transcriptase (hTERT).  Immortal PTECs (hTERT-PTECs) maintained both the morphological and functional characteristics of primary PTECs, as indicated by the expression of cytokeratin 18, cell-cycle analysis, proliferation assay, Western blotting, telomerase activity assay, karyotype analysis and quantitative RT-PCR.  Compared to primary PTECs, hTERT-PTECs had an extended replicative lifespan, higher telomerase activity, and enhanced proliferative activity.  In addition, this cell line resulted in a lack of transformed and grown tumors in nude mice, suggesting that it could be safely applied in further studies.  Moreover, hTERT-PTECs were vulnerable to all swine-origin mycoplasmas through quantitative analysis as indicated by 50% color changing unit (CCU₅₀) calculation, and no significant differences of adhesion ability between primary and immortal PTECs were observed.  For the representative swine mycoplasma Mycoplasma hyopneumoniae (Mhp), except for DNA copies quantitative real-time PCR assay, indirect immunofluorescence assay and Western blotting analysis also depicted that hTERT-PTECs was able to adhere to different Mhp strains of different virulence.  In summary, like primary PTECs, hTERT-PTECs could be widely used as an adhesion cell model for swine-origin mycoplasmas and in infection studies of various porcine respiratory pathogens.