engleski

Impaired electron transport in thylakoid membranes of young spruce needles exposed to high light stress

Photoinhibitory implications in photosynthetic apparatus of two developmental stages of Norway spruce (Picea abies L. Karst.) needles, current-year (CY, three months old) and previous-year (PY, one year older), were investigated. Chlorophyll a fluorescence of young (CY) and mature (PY) needles, collected early in the morning, was measured after acclimatization to the room temperature and after the stress treatment (HL, ~850 μmolm-2s-1 ; 291 0C ; 1 hour) conducted in growth chamber. The maximum quantum yield of photosystem II (PSII), Fv/Fm, measured before stress application showed fully functional PSII in both CY and PY needles. Increased performance index on absorption basis (PIABS) in PY revealed their higher overall photosynthetic efficiency. Light stress (HL) slightly decreased Fv/Fm in both, CY and PY needles, but remained high above limited value for PSII functionality (Fv/Fm>0.75). Specific fluxes per active reaction center (RC) including absorption (ABS/RC) and trapping of excitation energy (TR0/RC), electron transport (ET0/RC) and dissipation of excessive absorbed energy (DI0/RC) were also analyzed. CY needles had decreased PIABS and ET0/RC after stress treatment. Other fluxes per RC showed significantly higher values in CY, if compared with PY needles. In conclusion, we can highlight better acclimation response of mature needles under photoinhibitory light. In spite of the same primary photochemistry, young needles were strongly affected by light stress what was related to inhibited electron transport in thylakoid membranes.

Picea abies; high light stress; photoinhibition; chlorophyll a fluorescence; photosynthesis

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