Qualitative and quantitative analyses of the plasmodesmata that accompany cell fate changes during the somatic embryogenesis of

Abstract

Plasmodesmata (PD) are cytoplasmic and membrane-lined microchannels that enable symplasmic communication in plants, which is involved in the regulation of cell differentiation. The presented results emphasise the qualitative and quantitative analyses of PD, which are the basis of the symplasmic communication. The cells that initiate various development programmes create symplasmic domains that are characterised by different degrees of symplasmic communication. Changes in symplasmic communication are caused by the presence or absence of PD and/or the ability of signals to move through them. In the presented studies, somatic embryogenesis was used to describe the characteristics of the PD within and between the symplasmic domains in explants of the Arabidopsis thaliana (L.) Heynh ecotype Columbia-0 and 35S:BBM transgenic line. Transmission electron microscopy was used to describe the cells that regain totipotency/pluripotency during somatic embryogenesis, as well as the number and shape of the PD in the different symplasmic domains of the explants and somatic embryos. Array tomography was used to create a 3D reconstruction of the protodermal cells of the somatic embryos with particular emphasis on the PD distribution in the cell walls. The results showed that there were different frequencies of the PD within and between the symplasmic domain that emerges during somatic embryogenesis and between the Col-0 and 35S:BBM somatic embryos with regard to the differences in the shape of the PD.

Apoplastic and Symplasmic Markers of Somatic Embryogenesis

“…Symplasmic domains were determined for embryogenesis [ 66 , 81 , 82 , 83 , 84 ], androgenesis [ 85 ], and somatic embryogenesis [ 67 , 86 , 87 , 88 , 89 , 90 ].…”

“…The correlation between symplasmic domains and zygotic embryo development has been described for Arabidopsis and Sedum [ 66 , 82 , 83 , 88 , 89 ]. Studies on Arabidopsis showed that the zygotic embryo is a single symplasmic domain during all stages of development, but only for low molecular weight molecules (up to 0,5 kDa).…”

“…Comparisons of GFP (construct of varying sizes) movement in zygotic and somatic embryos of Arabidopsis showed that the symplasmic domains form similarly in both types of embryos. However, there are some qualitative differences such as the timing of establishing domain boundaries and the sizes of molecules that can move between symplasmic domains [ 88 , 91 ].…”

“…The movement of signals through PD is regulated not only by the regulation of PD SEL but also by the number of PD between cells implementing the same or different developmental programs. Analyses performed using TEM and 3D reconstruction methods ( Figure 3 ) and three different explants of A. thaliana for the SE induction showed that the number of PD between cells within the embryogenic symplasmic domain was the highest, followed by that between cells within the meristematic symplasmic domain, but the number of PD on the border of these symplasmic domains was the lowest [ 88 ]. During the SE of Pinus nigra , PD were only detected between the cells of embryogenic calli [ 106 ].…”