The potential of poly (ADP-ribose) polymerase (PARP) inhibitors to improve plant growth and yield: novel crop protection agents under stressed conditions

Chemical inhibition of the activity of poly (ADP-ribose) polymerases (PARPs) is associated with enhanced stress tolerance and growth in response to a broad range of abiotic plant stressors. This led to the suggestion that PARP inhibitors might have application in future crop protection strategies. However, the vast majority of studies to date have involved short-term, in vitro assays which are not representative of the conditions crop plants experience in the field. This work aimed to quantify the impact of chemical PARP inhibitor application on photosynthesis, growth and yield in planta, under well-watered and droughted conditions. In Chapter 2, a protocol for the quantification of the impact of drought stress on photosynthesis was developed, mainly using chlorophyll fluorescence imaging. In Chapter 3, the impacts of PARP inhibitors on photosynthesis, growth and survival in response to drought were measured. PARP inhibitors enhanced survival to severe stress but there was a cost associated with application under well-watered and moderate drought conditions. Chlorophyll fluorescence and growth measurements indicated that PARP inhibitors also had a damaging effect. Results from Chapter 4 suggested that PARP and PSII inhibitors had broadly negative impacts on yield. There was a strong relationship between growth (maximum plant object sum area) and yield under stress, which enabled the effects that compounds had on yield to be predicted approximately 40 days earlier than measuring at harvest. By fitting a model to the growth data it was possible to predict the impacts even earlier still. In Chapter 5, application of a PARP inhibitor reduced stomatal conductance but did not alter opening/closing kinetics, indicating the compound had an anti-transpirant effect. The enhanced stress tolerance of PARP-deficient plants likely protected against severe drought. However, a trade-off arises because of the costs associated with application under more moderate conditions. If PARP inhibitors are to be used in agriculture the cost/benefit balance will have to be carefully considered.