Photosynthetic and antioxidative strategies of flag leaf maturation and its impact to grain yield of two field-grown wheat varieties

Photosynthesis is the most important source of dry matter production directly influencing grain filling in wheat. Croatian winter wheat varieties, 'Vulkan' and 'Golubica' have similar genetic yield potential but in previous years 'Golubica' failed to achieve it. In order to find reasons of that, we evaluated photosynthetic (JIP test) and oxidative pathways (antioxidative enzymes and non-enzymatic components) in flag leaves of both wheat varieties from flowering till late milk development stage. The maximum quantum yield of PSII (TR0/ABS) and performance index on absorption basis (PIABS) during experimental period indicated functional photosynthetic process, but according to other JIP test parameters down-regulation of PSII occurred in flag leaves of both varieties. In leaves of variety 'Golubica', significant inactivation of active reaction centers altogether with enlargement of carotenoids content imply on induction of photoinhibition. Also, at oxidative metabolism level, increase of catalase activity, hydrogen peroxide and malondialdehyde content in flag leaves of variety 'Golubica' imply on structural and functional changes and oxidative stress state in cell. Changes of photosynthetic and oxidative metabolism level in flag leaves of variety 'Golubica' imply on earlier onset of senescence than in 'Vulkan'. Reduced time of photosynthetic product accumulation and its translocation into grain could be the reasons for 'Golubica' immanent underproduction.