Ks. Beach et al., Experimental analysis of rhodophyte photoacclimation to PAR and UV-radiation using in vivo absorbance spectroscopy, BOTAN MARIN, 43(6), 2000, pp. 525-536
Analysis of absorbance spectra of the red alga, Ahnfeltiopsis concinna, rev
ealed the capacity of tissues from the canopy and understory to respond to
changes in the intensity of photosynthetically active radiation. No differe
nces in photoacclimation responses were observed in the experiments perform
ed with A. concinna under PAR-only, PAR+UV-A, and PAR+UV-A+UV-B treatments.
In situ, photoacclimation capacities were manifested as marked alterations
in pigmentation for tissues from canopy to understory microsites in indivi
dual thalli of this dense tropical turf. This phenotypic adjustment is dyna
mic and recovery from irradiance stress induced by canopy removal simulatin
g herbivory or bleaching events is complete within 29 days. In vivo absorba
nce spectra allowed simultaneous observation of multiple pigment pools and
monitoring photoacclimation changes over the course of days in this alga. I
nsight into the cascade of photoacclimation events was revealed by concurre
nt measurement of pigments and photosynthetic performance. Overall, acclima
tion from a sun to shade or shade to sun states proceeded faster for degrad
ative than for synthetic processes. Specifically, phycobilin degradation in
tissues from understory microsites exposed to high photon flux density (PF
D) was faster than phycobilin synthesis in tissues from canopy microsites e
xposed to low PFD. Additionally, levels of phycoerythrin changed to a great
er relative extent than did shifts of compensation or saturation irradiance
thresholds for photosynthesis in acclimation from shade to sun conditions.
Compensation and saturation irradiances changed to a greater relative exte
nt than did levels of phycoerythrin in acclimation from sun to shade condit
ions. Lastly, carotenoid and putative mycosporine amino acid absorbances ad
justed in response to changes in quantity of incident photon flux regardles
s of light quality (PAR, UV-B, UV-A). This suggests a similar signal transd
uction mechanism or other metabolic linkages in this photoacclimation mecha
nism.