BSA Online Image Collection, Cellular Communication Channels

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Young parenchyma tissue cut parallel with the epidermis	Parenchyma cells in phloem of Cucurbita maxima leaf	Plasmodesmatal structure in longitudinal	Constictions at both ends of plasmodesma presumably have valve-like function	Plasmodesmata originating during cell division


Mitosis in longitudinal divisions of elongated cells	Late telophase (nuclei not shown)	Involvement of ER in formation of plasmodesmata	Cell plate has become the cell wall with fully formed plasmodesmata	Young sieve element and companion cell


Two stages in sieve plate development	Young wall with plasmodesmata sieve plate elements and companion cells	Further development of a pore site in longitudinal view	Continuous callose and plasmalemma in former plasmodesmal canal	Left, plugs of callose, penetrated by plasmodesmata, fill the pores. Right, pores open, lined with thin layer of callose


P-protein plug in pore	Cross sections through pores filled with P-protein	P-protein digestion with pepsin (left); control (right)	Plasmodesma connecting a sieve element (below) and branched plasmodesma located on the companion cell	Primary xylem of Phaseolus vulgaris stem, with ring-like and helical secondary walls


Removal of vessel end wall	Unperforated vessel wall parts	Partially hydrolyzed primary wall	Vessel member from Pelargonium leaf with perforations and pits