In higher plants the capacity for photosynthesis tends to saturate at high light intensities while the absorption of light remains linear. Therefore there exists the potential for the absorption of excess light energy by photosynthetic light harvesting systems. This excess excitation energy leads to an increase in the lifetime of singlet excited chlorophyll increasing the chances of the formation of long-lived chlorophyll triplet states by inter-system crossing.

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dbpprop:abstract
  • In higher plants the capacity for photosynthesis tends to saturate at high light intensities while the absorption of light remains linear. Therefore there exists the potential for the absorption of excess light energy by photosynthetic light harvesting systems. This excess excitation energy leads to an increase in the lifetime of singlet excited chlorophyll increasing the chances of the formation of long-lived chlorophyll triplet states by inter-system crossing. Triplet chlorophyll is a potent photosensitiser of molecular oxygen forming singlet oxygen which can cause oxidative damage to the pigments, lipids and proteins of the photosynthetic thylakoid membrane. One photoprotective mechanism that exists to counter this problem is the so-called non-photochemical quenching of chlorophyll fluorescence (NPQ) which relies upon the conversion and dissipation of the excess excitation energy into heat. NPQ involves conformational changes within the light harvesting proteins of photosystem II that bring about a change in pigment interactions causing the formation of energy traps. The conformational changes are stimulated by a combination of transmembrane proton gradient, the PsbS subunit of photosystem II and the enzymatic conversion of the carotenoid violaxanthin to zeaxanthin.
rdfs:comment
  • In higher plants the capacity for photosynthesis tends to saturate at high light intensities while the absorption of light remains linear. Therefore there exists the potential for the absorption of excess light energy by photosynthetic light harvesting systems. This excess excitation energy leads to an increase in the lifetime of singlet excited chlorophyll increasing the chances of the formation of long-lived chlorophyll triplet states by inter-system crossing.
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  • Non-photochemical quenching
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