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The unique feature of plant organisms is the presence of plasmodesmata (PD) between neigh- boring cells. Such plasmodesmatal continuum which exists within the plant body is termed symplasm. Classical view of plasmodesmata as static structures within the cell walls between neighboring cells must be reevaluated. According to our recent knowledge symplast is divided into functional domain. It appeared that symplasmic isolation/communication of cells or group of cells (symplasmic domains or symplasmic fields) is necessary for its proper differentiation within the plant body. Namely, plasmodesmata as a highly flexible structures regulate the diffusion of molecules including proteins and mRNA. This confirms the role of PD in the regulation of cells differentiation. For better understanding the role of symplasmic isolation/communication in cell differentiation basic information about plasmodesmata, symplasm and symplasmic transport are also described in presented paper. Some parameters of molecules diffusion in water, through plasmalemma and plasmodesmata, dynamic of plasmodesmata closure and opening (syn- thesis of callose and its digestion) under different conditions were also provided. Information about movement of proteins (KNOTTED 1, DEFICIENS, CLAVATA 3, LEAFY, APETALA 3) and RNA between different zones of apical meristem (tunica and corpus) were described in details, as these results were among the first which suggested that movement of signaling molecules through plasmodesmata exist and can influence cell differentiation. In presented article information about the role of symplasmic isolation during the differentiation of trichoblast and atrichoblast cells, changes within the embryo sac in connection with the fertilization, double fertilization, zygote and seed development were described. During the differentiation of trichoblasts and atrichoblasts the importance of signals movement between cells through plasmodesmata and changes in symplasmic communication were described on the example of Arabidopsis root [13, 78]. Genetic control of hair cells differentiation and the role of symplasmic communication in this process were also shown. In the case of embryo sac development of Torenia fournieri results from experiments where symplasmic communication was investigated with the use of fluorochrome of low molecular weight (LYCH) and dextrans (3, 10 and 40 kDa) were described [12, 22]. During the development of Arabidopsis thaliana seed, changes in plasmodesmata SEL were also shown [77]. The importance of symplasmic communication during zygotic and somatic embryogenesis were briefly described on the example of Arabidopsis embryo development. Presented article shows informa- tion about the symplasmic isolation between explantat and somatic embryo. Moreover, description of the analysis of ise2 mutants in connection with the symplasmic isolation was also presented. From all described examples it is evident that cell differentiation is connected with the decrease of the symplasmic communication between cells which undergo different fate during the development. It is also important to notice that plasmodesmata are not passive channels, but critical players in gene regulation, controlling intercellular transport of molecules between particular cells during development [94].
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Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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