01634nas a2200145   4500008004100000245009300041210006900134260000800203300001200211490000700223520117800230100001701408700001501425856004801440       2002                        eng d00aTetrad pollen formation in Annona (Annonaceae): Proexine formation and binding mechanism0 aTetrad pollen formation in Annona Annonaceae Proexine formation   cMay  a734-7470 v893 aMeiotic tetrads of Annona glabra and A. montana build up a well-developed proexine (protectum, probaculum, and pronexine) at the proximal side but only a thin pronexine at the distal side during the tetrad stage. The callosic envelope is only partially digested by the end of tetrad stage. The remaining, undigested part is composed of the intersporal mass and thin peripheral layers, and the latter is conjunct with the distal pronexine of the microspore. In this remaining callosic structure celluloses are also present. Later on, due to the continuous slow decomposition of this callose-cellulose structure and microspore expansion, microspores break up the callose-cellulose envelope. Because all the four microspores are bound together by the callose-cellulose structure, they move out of the chamber in rotation. Eventually the thin pronexine is pulled toward the center of the tetrad and the well-developed proexine becomes the distal wall. These descriptions of the partial digestion of callosic envelope, the transformation from a callose-cellulose structure to the binding system of tetrad pollen, and microspore rotation in Annona are unusual in the angiosperms.1 aTsou, C., H.1 aFu, Y., L.  uhttps://annonaceae.myspecies.info/node/561102351nas a2200361   4500008004100000020001400041245007900055210006900134260000800203300001000211490000800221520137900229653001601608653001101624653001501635653003101650653002401681653002201705653002001727653001701747653001801764653001101782653001401793653001101807653002401818653001701842653002601859653001201885653001201897100001701909700001501926856004801941       2007                        eng d  a0378-269700aOctad pollen formation in Cymbopetalum (Annonaceae): the binding mechanism0 aOctad pollen formation in Cymbopetalum Annonaceae the binding me  cJan  a13-230 v2633 aOur recent study of tetrad pollen formation in Annona (Annonaceae) revealed that after meiosis the callose-cellulose envelope forms a special conjugation with individual microspores and the forthcoming callose digestion is incomplete. The undigested part forms a central binder holding the four microspores of the tetrad together. This process causes the microspores to rotate 180 degrees. In this paper we describe pollen formation in another annonaceous genus, Cymbopetalum, in which the pollen is shed in octads, through use of light microscopy, epifluorescence microscopy, and TEM. In Cymbopetalum, two meiocytes, connected by abundant cytomictic channels, are produced in each sporangium. Octad pollen formation in Cymbopetalum is shown to be comparable to the synchronized formation of two connected Annona tetrads, which then integrate into a single octad. Unique features of Annona polyad formation, e.g. special binding between the callose-cellulose envelopes and microspores, incomplete callose digestion, and microspore rotation, also occur in Cymbopetalum. In addition, formation of the Cymbopetalum octad involves development of a cushion-like structure that binds the distal pronexine of all eight microspores, and there is the production of intine protrusions. The evolutionary origin of the callose-cellulose binding mechanism within the family is discussed.10aangiosperms10aAnnona10aAnnonaceae10aASIMINA-TRILOBA ANNONACEAE10aCALLOSE DISSOLUTION10acallosic envelope10acompound pollen10aCymbopetalum10aDEVELOPMENTAL10aEVENTS10aEVOLUTION10aGENERA10amicrospore rotation10aoctad pollen10aSPORODERM DEVELOPMENT10aTAPETUM10aTETRADS1 aTsou, C., H.1 aFu, Y., L.  uhttps://annonaceae.myspecies.info/node/5612