ABSTRACT
Some mosses are extremely tolerant of drought stress. Their high drought tolerance relies on their ability to effectively dissipate absorbed light energy to heat under dry conditions. The energy dissipation mechanism in a drought-tolerant moss, Bryum argenteum, has been investigated using low-temperature picosecond time-resolved fluorescence spectroscopy. The results are compared between moss thalli samples harvested in Antarctica and in Japan. Both samples show almost the same quenching properties, suggesting an identical drought tolerance mechanism for the same species with two completely different habitats. A global target analysis was applied to a large set of data on the fluorescence-quenching dynamics for the 430-nm (chlorophyll-a selective) and 460-nm (chlorophyll-b and carotenoid selective) excitations in the temperature region from 5 to 77 K. This analysis strongly suggested that the quencher is formed in the major peripheral antenna of photosystem II, whose emission spectrum is significantly broadened and red-shifted in its quenched form. Two emission components at around 717 and 725 nm were assigned to photosystem I (PS I). The former component at around 717 nm is mildly quenched and probably bound to the PS I core complex, while the latter at around 725 nm is probably bound to the light-harvesting complex. The dehydration treatment caused a blue shift of the PS I emission peak via reduction of the exciton energy flow to the pigment responsible for the 725 nm band.
Subject(s)
Bryopsida/physiology , Chlorophyll/chemistry , Photosystem I Protein Complex/chemistry , Antarctic Regions , Bryopsida/chemistry , Chlorophyll/metabolism , Dehydration , Droughts , Energy Transfer , Japan , Light , Models, Biological , Photosystem I Protein Complex/metabolism , Photosystem II Protein Complex/chemistry , Photosystem II Protein Complex/metabolism , Spectrometry, Fluorescence/methods , TemperatureABSTRACT
We examine the droplet motion in one-component fluids in a small temperature gradient by solving linearized hydrodynamic equations supplemented with appropriate surface boundary conditions. We show that the velocity field and the temperature around the droplet are strongly influenced by first-order phase transition taking place at the interface. Latent heat released or absorbed at the interface drastically changes the hydrodynamic flow around the droplet. As a result, the temperature becomes almost homogeneous inside the droplet and the Marangoni effect arising from the surface tension gradient is much suppressed. The droplet velocity is also much decelerated.
