Marine diatoms live in the marine environment where water stirs constantly. Therefore, marine diatoms utilize various mechanisms to enhance heat dissipation when they are subjected to drastic fluctuations in the light intensity. In heat dissipation mechanism, non-photochemical fluorescence quenching (NPQ) is one of the important ways to dissipate heat. There are many factors to induce NPQ, we found that lumen acidification of thylakoid,electron transport in the photosynthetic system, pigment cycle and the activation of light harvest complex proteins are the main reasons. We used the model diatom Thalassiosira pseudonana to investigate the factors controlling the kinetics of NPQ. By adding chemicals to cells exposed to excess light, we found thatlumen acidification could be the main reason to induce NPQ. And lumen acidification could also induce the pigment cycle, thus speeding up the excess energy dissipation. In the experiments of cutting linear electron flow of photosynthetic system, we found when the photochemical fluorescence quenching way is restrained, more NPQ will be induced. But the electron transfer inhibition doesn't seem to induce pigment cycle to dissipate excess energy. Pigment cycle may be a kind of auxiliary heat dissipation mechanism to cope with light stress in T. pseudonana. During HL exposure, the up-regulation of the light harvesting complex protein ×6 (Lhcx6) and Lhcx genes suggests that they are involved in photo-protection. Lhcx6 protein may play a key role in managing light responses in T. pseudonana.
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