Abstract Detail

The Stress of Life with Light:: a Graeme Berlyn retrospective

Thorhaug, Anitra [1], Berlyn, Graeme P. [2].

Spectral reflectance responses of tropical and temperate seagrasses to diminishing colored light and low salinity stimuli: Thalassia testudinum ,Halodule wrightii, Syringodium filiforme, and Zostera mari.

Seagrasses are the sole flowering plants totally submerged in seawater. Re-evolving into the marine environment from the terrestrial necessitated major physiological adaptations: 1.) to the sea’s green-blue light regime; and 2.) to variable high salt concentrations. Seawater's effects blocks red and orange light with depth. Our results measured spectral reflectance of whole living plants' responses to colored light and salinity of Thalassia testudinum, Zostera marina , Halodule wrightii, and Syringodium filiforme. The responses of seagrasses' accessory pigments were inversely related to light intensity during incubation in blue or green light. The absorption of accessory pigments (400 to 520 nm) was higher for all colors at diminished light levels than the chlorophylls a and b. These xanthophylls' and carotenoids' energetic responses explain differences between action spectra and pigment spectra (460 nm to 530 nm). The low light activation in blue-green light occurred in all four species. In Zostera green light responses appear to be similar to the responses blue light, but in most cases of lesser magnitude. As the colors change in all species, the red edge effect appears similar in shape, while the green edge effects appears to differ in wavelength of commencement, response magnitude and shape. In all cases for blue and green light, the partial absorption in the accessory pigments was a larger magnitude than the chlorophyll a absorption response at 680 nm. When the seagrasses are in red high light (75%), photooxidation of chlorophyll occurs. In blue and green light, the diminished levels are stimulatory because less chlorophyll is destroyed by high green or blue light, than in the high red and orange light. We hypothesize that green light, even at high levels, is preserving the chlorophylls. High green and blue light are demonstrating absorption. Levels of salinity below 16 ppt create senescent-like responses statisitically differing form those above 20 ppt with three species, Zostera has this response, but at lower salinities than 16 ppt.

Broader Impacts:
The evolutionary mechanisms by which seagrasses separated from all flowering plants to reemerge permanently into the marine environment has been speculated on widely, but the genetic material is too poorly understood to trace the evolutionary physiological pathways. Responses to blue and green light are an absolute neccesity for the ermergence process. For the first time this elucidates capacity of 4 dominant seagrasses to deal with green and blue light as found in deeper marine and estuarine waters constrasted to red and organce light found in terrestrial environment and in very shallow and intertidal marine environment. Additionally totally new data for spectral reflectance is presented giving information for profiling from remote sensing 4 species signatures living at oceanic depths vs. shallows.

1 - Yale University, School of Forestry and Environmental Sciences, Greeley Laboratories 375 Prospect St., New Haven, Connecticut, 06901, USA
2 - Yale University, School of Forestry and Environmental Studies, Greeley Memorial Laboratory, 370 Prospect Street, New Haven, CT, 06107, USA

Keywords:
Spectral reflectance
Thalassua testudinum
Syringodium filiforme
Zostera marina 
Halodule wrightii
blue light
red light
green light
orange light
white light
carotenoids
xanthophylls
chlorophyll a
chlorphyll b.

Presentation Type: Symposium or Colloquium Presentation
Session: SY5
Location: 554/Convention Center
Date: Wednesday, August 4th, 2010
Time: 10:30 AM
Number: SY5007
Abstract ID:167