In order to study vegetation evolution and environmental changes around 2.5 Ma B.P., a total of 146 pollen samples with an average time resolution of 7 000 years were analyzed in the deep-sea record at the depth of 13...In order to study vegetation evolution and environmental changes around 2.5 Ma B.P., a total of 146 pollen samples with an average time resolution of 7 000 years were analyzed in the deep-sea record at the depth of 135 - 95 m （in composition depth） from ODP Site 1143 （9° 22＇ N, 113° 17＇ E） in the southern South China Sea. The results show that the pollen influx has a distinct change. During 2.6 - 2.0 Ma B.P., the average value of pollen influx increased evidently compared with that of 3.0 - 2.6 Ma B.P. It shows that the sea level of SCS dropped dramatically around 2.6 Ma B.P., corresponding to the formation of the Northern Hemisphere ice-sheets and the enhancement of the East Asian Monsoon. The pollen influx variations reflect the glacial-interglacial cycles corresponding with the deep-sea oxygen isotope curve and indicate that the sea level of SCS rose and dropped many times after 2.6 Ma B.P. The spectrum analysis results of pollen influx show that there are cycles at 0.1Ma （eccentricity） and 46.9 ka （obliquity） during 3.0 - 2.0 Ma B.P.展开更多
In angiosperm, pollen wall formation is a critical step for male gametophyte development. Pollen wall constitutes of the outer layer exine and the inner layer intine. Exine is further divided into sexine and nexine. I...In angiosperm, pollen wall formation is a critical step for male gametophyte development. Pollen wall constitutes of the outer layer exine and the inner layer intine. Exine is further divided into sexine and nexine. In Arabidopsis, the general process of pollen wall formation has been reported. However, the nexine formation has not been revealed. Here, we observed the process of pollen wall formation in Arabidopsis thaliana using transmission electron microscope. After callose wall is formed, the primexine is present between plasma membrane and the callose layer in the tetrad. With plasma membrane undulation, sporopollenin precursors accumulated on the peak of undulated membrane which is further developed into probacula. The primexine determines plasma membrane undulation and sporopollenin accumulation based on previous analysis of an undulation-deficient mutant. Some materials obviously different from sporopollenin are filled between the primexine and plasma membrane. These materials cover all the surface of plasma membrane and gradually develop into nexine. After microspore is released from tetrad, the nexine layer is formed and the probacula is further developed into sexine with continued accumulation of sporopollenin. Based on these observations, we proposed a developmental model of early pollen wall formation.展开更多
基金the National Natural Science Foundation of China projects （40371116） the National Major Basic Research Program of China （G200078502）.
文摘In order to study vegetation evolution and environmental changes around 2.5 Ma B.P., a total of 146 pollen samples with an average time resolution of 7 000 years were analyzed in the deep-sea record at the depth of 135 - 95 m （in composition depth） from ODP Site 1143 （9° 22＇ N, 113° 17＇ E） in the southern South China Sea. The results show that the pollen influx has a distinct change. During 2.6 - 2.0 Ma B.P., the average value of pollen influx increased evidently compared with that of 3.0 - 2.6 Ma B.P. It shows that the sea level of SCS dropped dramatically around 2.6 Ma B.P., corresponding to the formation of the Northern Hemisphere ice-sheets and the enhancement of the East Asian Monsoon. The pollen influx variations reflect the glacial-interglacial cycles corresponding with the deep-sea oxygen isotope curve and indicate that the sea level of SCS rose and dropped many times after 2.6 Ma B.P. The spectrum analysis results of pollen influx show that there are cycles at 0.1Ma （eccentricity） and 46.9 ka （obliquity） during 3.0 - 2.0 Ma B.P.
基金supported by the Major Research Plan from the Ministry of Science and Technology of China(2013CB945100)Innovation Program of Shanghai Municipal Education Commission(12YZ090)
文摘In angiosperm, pollen wall formation is a critical step for male gametophyte development. Pollen wall constitutes of the outer layer exine and the inner layer intine. Exine is further divided into sexine and nexine. In Arabidopsis, the general process of pollen wall formation has been reported. However, the nexine formation has not been revealed. Here, we observed the process of pollen wall formation in Arabidopsis thaliana using transmission electron microscope. After callose wall is formed, the primexine is present between plasma membrane and the callose layer in the tetrad. With plasma membrane undulation, sporopollenin precursors accumulated on the peak of undulated membrane which is further developed into probacula. The primexine determines plasma membrane undulation and sporopollenin accumulation based on previous analysis of an undulation-deficient mutant. Some materials obviously different from sporopollenin are filled between the primexine and plasma membrane. These materials cover all the surface of plasma membrane and gradually develop into nexine. After microspore is released from tetrad, the nexine layer is formed and the probacula is further developed into sexine with continued accumulation of sporopollenin. Based on these observations, we proposed a developmental model of early pollen wall formation.
