Reactive Oxygen Species Generation and Impact of Allopurinol in Hybrid Necrosis in Wheat.

Hybrid necrosis in wheat (Triticum aestivum L.) is the gradual death of leaves or plants caused by interaction of two dominant complementary genes Ne1 and Ne2 located on chromosomes 5B and 2B, respectively. Higher reactive oxygen species (ROS) generation has been described as the triggering factor for programmed cell death (PCD) in hybrid necrosis. The enzyme xanthine oxidase (XO) localized in the peroxisomal matrix is reported to be responsible for the production of ROS in several host-pathogen/insect interactions. In this study, we quantified the total ROS generation through hydrogen peroxide (H₂O₂) in hybrid necrosis exhibiting F₁ hybrids and their parents (i.e. bread wheat cultivar ‘Alsen’ and synthetic hexaploid wheat TA 4152-37) planted in greenhouse.  The effect of soil drenched allopurinol, a xanthine oxidase inhibitor, on overall progression of hybrid necrosis and ROS generation were also evaluated. ROS was measured from 1^st, 2^nd, and 5^th leaves of the plants before and during necrosis progression.  Higher ROS generation was not observed either before or during necrosis progression in F₁ hybrids. However, there was decreased ROS production during the progression of necrosis. The trend of ROS production in F₁ hybrid was similar or even lower than in the parents having no necrosis. This suggests that higher generation of ROS is not always necessary for triggering PCD during hybrid necrosis.  Furthermore, use of allopurinol did not significantly influence ROS generation or overall agronomical performances.  This indicates that xanthine oxidase may not be the only source of ROS generation in hybrid necrosis.