Quantitative variations of nuclear DNA during plant development: A critical analysis

In this review a critical analysis is made of the quantitative DNA variations that take place during plant development. These include underreplication, loss and amplification of repeated sequences; particular attention is devoted to quantitative variations of non-coding DNA sequences. Examples reported in the literature are analysed in relation to the differential biological phenomena they accompany such as vegetative development, phase changes, senescence, dedifferentiation or tumour formation. The author also considers the influence that external elements such as growth factors, chemical substances, culture medium composition, or, also, different stimuli of environmental character, can have on these quantitative variations of nuclear DNA sequences. Finally the different hypotheses on the role that repetitive DNA sequences (particularly those that are highly repeated) can have on the life of the cell are analysed and discussed. The experimental evidence, although fragmentary and sometimes contradictory, leads to the conclusion that the plant genome is not so 'quantitatively static' as was once thought, but is instead characterized by a dynamic plasticity; the role of repeated DNA sequences in the plant development seems to be much more active, than the role hypothesized by many authors in the past.