Alterations of the photochemical efficiency of photosystem II in wheat (Triticum aestivum L.) seedlings exposed to antimycin A and heat stress

The effect of antimycin A (AA) as a possible activator of the alternative pathway (AP) was assessed on photosynthetic pigment composition and chlorophyll (Chl) fluorescence parameters in response to heat stress (HS) (42 degrees C) in etiolated wheat (Triticum aestivum L., var. Harmony) seedlings. Results indicate that pigment concentrations significantly decreased (20-70%) following long-term HS, while the short-term exposure resulted in a 16-56% decline in etiolated wheat seedlings. It was observed that short-term and long-term HS altered photosystem (PSII) functionality in leaves, which was evidenced by a low maximum photochemical efficiency of PS II (F-v/F-m,), a maximum fluorescence yield in the dark-adapted state (F-m), and by a high minimal fluorescence yield in the dark-adapted state (F-0). However, at the same time AA reduced the negative effect of HS, suggesting that the activation of the AP induced by AA displayed tolerance to stress contributing the stabilization of the photosynthetic apparatus in etiolated wheat seedlings under HS.