DNA and desiccation tolerance

Abstract

This article reviews mechanisms by which specialized cells of different life forms have overcome the lethal effects of dehydration and considers how the maintenance of genetic information is central to survival As a dynamic and hydrated moleculein vivo, DNA can assume different conformational structures depending upon the water activity, the base sequence and the presence of specific binding proteins The attainment of stable secondary structures that are resistant to degradation in vivo at low water potentials is proposed as a likely accompaniment to desiccation tolerance In addition, chemical modification of bases in DNA, the extent of methylation and conformational changes could determine the expression of different gene sequences as cells pass from desiccation-tolerant to desiccationintolerant states We monitored the integrity of extracted DNA in embryos of seeds and in winddispersed pollen during transition from their desiccation tolerance to desiccation intolerance on hydration and germination. We present evidence to show that the DNA of these two stages is different and that it is the DNA from desiccation-tolerant cells only that retains integrity when the cells are subjected to desiccation regimes We discuss these findings in relation to certain hydration-sensitive DNA structures and to other relevant biological systems

Seed Germination and Dormancy.

“…The first takes place soon after imbibition and probably involves the repair of DNA damaged during maturation drying and rehydration as well as the synthesis of mitochondrial DNA. DNA synthesis associated with postgerminative cell division accounts for the second phase (Figure 1 ; Zlatnova et al, 1987;Osborne and Boubriak, 1994).…”

Tolerância à dessecação em sementes

“…Osborne & Boubriak (1994) verificaram que apenas o DNA das células de embriões tolerantes à dessecação mantinham sua integridade durante a secagem. Porém, o controle da produção de proteínas, ora voltadas ao desenvolvimento da semente, ora à germinação e ao crescimento da plântula, é feito por RNAs-m. Em sementes de feijão e de mamona, a desidratação paralizou a produção de RNAs-m voltados ao desenvolvimento da semente, ao mesmo tempo em que os RNAs-m residuais eram degradados; enquanto isso, eram produzidos RNAs-m associados com a germinação e com o crescimento das plântulas.…”

Herbicide Phytotoxicity and Resistance to Herbicides in Legume Plants

“…Maintaining the integrity of genetic material and keeping the DNA repair mechanisms functional during dehydration are the most important for seed survival. As a result of water loss during seeds desiccation the genetic material undergoes conformational changes, depending on its nucleotide sequence and interactions with specific DNA-binding proteins (Osborne & Boubriak, 1994). A higher stability of seed DNA structure probably indicates increased seed tolerance to desiccation.…”