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STUDIES ON THE CALCIUM DISTRIBUTION IN DEVELOPING SYNERGIDS OF LETTUCE(Lactuca sativa L.)

QIU Yi Lan~(1,2) LIU Ru Shi~(1,2) TIAN Hui Qiao~2 (~1School of Life Sciences,Hunan Normal University,Changsha 410081,~2School of Life Sciences,Xiarnen University,Xiamen 361005)  
Potassium antimonite was used to locate calcium in the synergids of lettuce (Lactuca sativa L) during their development.The two synergids on 3d before anthesis formed evident polarity with most cytoplasm located in the micropylar end and nucleus in the middle and a big vacuole in the chalazal end.At this time,calcium precipitates were a few in both cells.Calcium precipitates in the two synergids began to increase on 2d before anthesis.Synergid wall in the micropylar end thickened on ld before anthesis,in which many calcium precipitates located.Near anthesis,synergids formed filiform apparatus in which abundant calcium precipitates accumulated to prepare for attract- ing pollen tubes entering.At anthesis,the distribution of calcium precipitates between two synergids was the same.At 1h after pollination,calcium precipitates evidently increased in one synergid that seemed to degenerate,the other one was persistent and the distribution of calcium granules did not change.Two synergids kept intact at 1d after emasculated,and the distribution of calcium precipi- tates did not display difference,suggesting that the degeneration of one synergid was caused by ap- proaching pollen tubes which might give some signal to induce calcium increase of the synergid.Be- fore fusion of sperm cell with egg cell,the cytoplasm of degenerated synergid embraced the egg and formed a thin layer between the egg and the central cell.Calcium precipitates in the different parts of degenerated synergid were closely connected with the fertilization:calcium precipitates accumulat- ed in the near ehalazal end of degenerated synergid at 1h after pollination.At 2.5h after pollination, the calcium precipitates increased at the chalazal end,especially abundant in the thin layer between the egg and the central cell.However,at 4h after pollination,the fertilization had finished at this time,the distribution of calcium precipitates in degenerated synergid changed again:the precipitates decreased at the chalazal end and increased at the micropylar end.The above-mentioned results sug- gested that calcium in the degenerated synergid played an important role during lettuce fertilization.
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