Arabidopsis thaliana ecotypes from warmer climates display greater thermal dissipation of light energy when grown in a common garden in Germany

Background/Question/Methods

Plants have evolved protective mechanisms to safely dissipate excess light energy. One of these mechanisms is thermal dissipation by way of the xanthophyll pigment cycle when violaxanthin is converted to zeaxanthin. Thermal dissipation can be measured as non-photochemical quenching (NPQ) using chlorophyll fluorescence. Cold temperatures or dry conditions that slow photosynthesis without reducing light capture can lead to an increase in excess absorbed energy. Thus, plant populations from cold or dry climates may have evolved greater capacity for thermal dissipation. To test for genetic variation among populations in NPQ associated with climate of origin, we measured midday NPQ levels in over 60 ecotypes of Arabidopsis thaliana growing in a common garden in Germany during March. The amount of each xanthophyll pigment in a leaf at midday was measured with HPLC. As mentioned above, ecotypes from colder climates may be expected to display greater NPQ levels, possibly due to higher intrinsic pool sizes of xanthophyll pigments and/or greater conversion of xanthophylls to zeaxanthin. Alternatively, ecotypes from colder climates may be expected to display smaller NPQ levels if they have evolved higher photosynthetic rates at cold temperatures. 

Results/Conclusions

Regression analysis supports the second alternative. There was a small but significant positive correlation of NPQ with the mean March temperature of origin, i.e. colder climate ecotypes exhibited smaller levels of NPQ. The proportion of xanthophylls as zeaxanthin was positively correlated with NPQ values. Thus, ecotypes from colder climates may require less xanthophyll cycle mediated energy dissipation at low temperatures than ecotypes from warmer climates due to higher photosynthetic rates at low temperature.