| Summary: | Mechanically isolated cell cultures were chosen as a model system to examine wound-induced dedifferentiation at the molecular level as large quantities of physiologically and morphologically similar G1-arrested mesophyll cells could be obtained. Within 5 days of culture such non-dividing, photosynthetic cells become heterotrophic, and have completed a first nuclear division and cytokinesis. There are few changes in cell morphology during the first 2-3 days in culture. However, during this period there is a massive increase in respiration rate and total RNA synthesis. Following DNA synthesis there is a rapid cell expansion, mitosis and cytokinesis. Steady state transcript populations were monitored through the first 8 days of culture by analysis of the products of in vitro translations on 2-D gels. Large changes in gene expression were evident during the first 3 days in culture with several genes highly up-regulated and others down-regulated. Dedifferentiation can be separated into 3 different phases. Firstly, reactivation of the cell cycle during which there are few cytological or physiological changes but gross changes in the expression of genes possibly associated with wounding or stress. Secondly, DNA synthesis, first mitosis event and phragmoplast formation during which there are minor changes in transcript abundance. Finally a continuation of the cell cycle with little alteration in transcript abundance. Changes in plastid morphology are only apparent after 10-14 days resulting in the formation of proplastid like structures. However, mRNA for both large subunit ribulose bisphosphate carboxylase and small subunit ribulose bisphosphate carboxylase decrease to basal levels within a day of culture and photosynthetic capacity diminishes when the first cell division is evident. Plastid dedifferentiation can therefore be considered separately and proceeds slowly being more or less complete after 2-3 cell divisions. Dedifferentiation is therefore seen to be a complex process which involves the interaction of several factors i.e wounding and hormones and results in temporal changes in transcript abundance, changes in the mode of respiration, morphology and cell proliferation.
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