| Popis: |
Photosynthesis, a process utilising energy of arriving photons for driving electron transport chain creating transmembrane pH gradient, is a widespread way of subsistence in the nature. However, the intensity of sunlight can exceed the rate which the organisms are able to manage by their gadgetry. In this situation, essential protective mechanisms, safely draining the excess energy away, take a turn. Many theories about the principle and regulation of these functions have been developed and new still arise. It appears that the attention focuses mainly on the antenna complex LHCII. It is possible to state that with high probability, the protective processes are assured by several mechanisms, and quite a stable opinion prevails that crucial role in their activation is played by decreasing pH. That is logical since the more photons come, the more intensively the transport of protons across the membrane happens, thus ΔpH reflects the balance between ATP usage and the membrane apparatus illumination. Generally, the phenomenon is called NPQ (non-photochemical quenching), because it weakens the chlorophyll fluorescence. An important task is probably handled by carotenoids, mainly zeaxanthin, created by violaxanthin deepoxidase at low pH; it provides chlorophylls with energetical trap during excitation... |
