Poster: Oxidative stress

Abs # 65: Poly(ADP-ribosyl)ation activity in plants affects energy homeostasis, cell death and stress tolerance

Presenter:	De Block, Marc , marc.deblock@bayercropscience.com
Authors	De Block, Marc  (A)   Verduyn, Christoph  (A)   De Brouwer, Dirk  (A)   Cornelissen, Marc  (A)
Affiliations:	(A): Bayer BioScience N.V.

Plants metabolize like animals polymers of ADP-ribose by means of the enzymes poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG). In plants two parp genes have been identified: parp1 and parp2. Both PARPs are known to be activated by DNA strand breaks caused by e.g. stress induced radicals. By activation they synthesize polymers of ADP-ribose on a range of nuclear enzymes using NAD⁺ as substrate. Subsequently, these polymers are hydrolysed by PARG. Numerous reports in the animal field indicate that over-activation of PARP in combination with PARG-activity causes a rapid breakdown of the NAD⁺ pool. This results in a stimulation of resynthesis of NAD⁺ using two to five molecules of ATP for each molecule of NAD⁺. In this way the cellular ATP reserves are depleted and leads to necrotic cell death. Here we show that in plants strong stresses activate PARP and cause cell death. Moreover, when the PARP-activity is reduced by means of chemical inhibitors or by silencing of the parp or parg genes, explants and whole plants become tolerant to a broad range of abiotic stresses. Our data indicate that the basis of this stress tolerance is the maintenance of energy homeostasis without enhancement of the mitochondrial respiration, minimizing the production of reactive oxygen species.