Tải bản đầy đủ - 0 (trang)
 Presence and Dynamics of UVR-Absorbing Compounds in Patagonian Macroalgae

 Presence and Dynamics of UVR-Absorbing Compounds in Patagonian Macroalgae

Tải bản đầy đủ - 0trang

208



E. WALTER HELBLING ET AL.



for Patagonian macroalgae that are subjected to high radiation levels and suffer

desiccation, especially during low tides and at summer time. Studies dealing with

these compounds in Patagonian macroalgae have focused on two main aspects:

(a) to determine their presence and abundance in key species of the community

and (b) to assess their dynamics throughout daily cycles and considering the tide

effects. These studies are particularly important in the context of climate change,

as they give insight into the capacity of different algae to cope with increasing

solar radiation.

Specific studies were carried out with the two strains of the Rhodophyte

Corallina officinalis (i.e., low- and mid-eulittoral forms). High-performance liquid

chromatography (HPLC) analysis indicated the presence of two MAAs, shinorine

and palythine, with the absolute concentration of the latter being about tenfold

higher than that of the former (Fig. 4). The amount of MAAs in low-eulittoral

samples was significantly lower than that in the mid-eulittoral strain. Significant

diurnal changes in the MAAs concentration and in the ratio between shinorine

and palythine of the low-eulittoral Corallina algae were also observed (Richter

et al., 2006): Both MAAs concentration increased around local noon, but the

ratio between shinorine and palythine decreased during midday owing to a higher

increase in palythine over shinorine (Fig. 4). In the afternoon, the MAAs concentration decreased again. In the mid-eulittoral strain, MAAs dynamics showed an

opposite pattern so that around noon the palythine concentration decreased compared with shinorine, whereas in the afternoon the palythine concentration

tended to increase. Although the data indicate a strong influence of solar radiation on MAAs synthesis in C. officinalis, it is still an open question, whether

endogenous circadian or circatidal rhythms are also involved in this process.

Concentration of UV-absorbing compounds and photosynthetic pigments as a function of different radiation treatments throughout daily cycles

were done with the Rhodophyte Porphyra columbina. Five MAAs were identified: mycosporine–glycine, shinorine, porphyra-334, palythine, and asterina.

Porphyra-334 was the most abundant MAA (~80% of the total concentration)

and it was always present regardless of the conditions under which the algae

were exposed. Shinorine was also present in high concentrations (~20%),

whereas the remaining MAAs occurred at much lower concentrations.

UV-absorbing compounds in P. columbina generally decreased throughout the

daily cycles in the two radiation treatments implemented (i.e., PAR+UVR and

PAR only) but, in contrast to Corallina officinalis, higher values were determined at night; also, and in general, slightly lower values at the end of the

experiment were determined in samples exposed only to PAR. The concentration of photosynthetic pigments, on the other hand, remained low throughout

the experiment. Results from ammonium-enrichment experiments on the synthesis of MAAs and photosynthetic pigments (Korbee Peinado et al., 2004)

showed no significant increase in the concentration of MAAs during a 6-day

exposure at concentrations of 0 and 50 mM NH4+. On the other hand, samples



209



ULTRAVIOLET RADIATION EFFECTS ON MACROALGAE



0.3



3



0.2



2



0.1



1



A



0

0



0

2



4



6



8



10



12



14



16



18



20



22



24



b 0.4

Shinorine (mg gDW−1)



Palythine (mg g DW−1)



4



4



0.3



3



0.2



2



0.1



1



Palythine (mg g DW−1)



Shinorine (mg gDW−1)



a 0.4



B



0



0

0



2



4



6



8



10



12



14



16



18



20



22



24



Local time

Figure 4. Diurnal changes in concentration (mg/g DW) of the MAAs shinorine and palythine in

Corallina officinalis growing in the low eulittoral (a) and in the mid-eulittoral (b) zones. Data are the means

and standard deviation of five independent measurements of different samples collected at the corresponding time. Differences between midday low eulittoral samples and morning or evening samples

in shinorine are significant (P < 0.05) and highly significant (P < 0.001) in palythine. Differences between

midday samples and morning or evening samples were only significant (P < 0.05) for palythine but not

for shinorine. (After Helbling et al., 2004.)



grown at 300 mM NH4+ had a significant increase compared with the initial

value and other treatments at day 6. In addition, and after 3 days of exposure,

the content of MAAs was significantly lower in thalli exposed only to PAR

compared with treatments receiving additionally UV-A and UVR, indicating

a stimulation of MAA synthesis in these treatments.



210



E. WALTER HELBLING ET AL.



The daily variations of UV-absorbing compounds in Ceramium sp. exposed

to full solar radiation followed approximately the daily irradiance cycle, with

high concentrations during the day and decreasing in the evening; during the day,

their concentration in samples exposed to UVR was significantly higher than in

those exposed only to PAR. Callithamnion gaudichaudii displayed high variability

in the concentration of UV-absorbing compounds in algae exposed to full solar

radiation, with significantly higher values during early morning and decreasing

during the day.

A comparison of the co-variation of UV-absorbing compounds as a function

of chlorophyll a in seven macroalgae species is shown in Fig. 5. UV-absorbing

compounds had a wide range of responses according to the species: In C. officinalis

and P. columbina exposed to full solar radiation, a significant positive correlation

was observed. On the other hand, in Ceramium sp and in C. gaudichaudii a poor

correlation between these compounds was found. Small amounts of UV-absorbing

compounds were found in Ulva rigida, Dictyota sp., and Enteromorpha linza.

Carotenoids, however, showed a significant positive correlation with chlorophyll a

in species studied (carotenoids = 0.9 * chl a, R2 = 0.89, P < 0.0001).



50



Ceramiun

Calithamnion

Corallina

Enteromorpha

Dictyota

Porphyra

Ulva



OD330 (g FW)−1



40



30



20



10



0

0



5



10



15



20



25



OG665 (g FW)−1

Figure 5. Mean absorption characteristics of UV-absorbing compounds (OD at 330 nm/fresh weight

(FW)) of Ceramium sp., Callithamnion gaudichaudii, Corallina officinalis, Porphyra columbina, Enteromorpha linza, Dictyota sp., and Ulva rigida exposed to UVR as a function of chl a concentration

(OD(665 nm)/FW). (After Helbling et al., 2002.)



211



ULTRAVIOLET RADIATION EFFECTS ON MACROALGAE



6. Algae as Food for Other Organisms

Macroalgae, as well as the environment where they grow, offer shelter and food for

diverse organisms, mainly invertebrates. Although many studies have been carried

out in different locations to evaluate the effects of solar radiation on the interactions

between macroalgae and other organisms, very few studies have addressed this topic

in the Patagonia area (Menchi, 2001; Helbling et al., 2002). Particularly, these studies

evaluated the impact of UVR on the survival of the amphipod Ampithoe valida and

the isopod Idothea baltica feeding on different macroalgae and differentially bioacumulating UV-absorbing compounds. The relationship between the optical density at

334 nm (i.e., an estimator of the concentration of UV-absorbing compounds) in the

crustaceans and that of their diets is shown in Fig. 6. In I. baltica (Fig. 6a), there was



OD334 I. baltica



a



5

4

3

2

1

0

0



OD334 A. valida



b



1

2

Codium Enteromorpha



3



4



5

Polysiphonia



6



8

6

4

2



Enteromorpha



Polysiphonia



0

0



1



2



3



4



5



6



OD334 macroalgae

Figure 6. Optical density at 334 nm (OD334) in crustaceans as a function of OD334 in the macroalgae

diet. (a) I. baltica; (b) A. valida. The symbols indicate the different algae used in this study: Codium sp.

(▲) collected during February 2001; Enteromorpha sp. (●) collected during February and June 2000

and February 2001, and Polysiphonia sp. (■) collected during February 2000. The vertical and horizontal lines are the standard deviation.



212



E. WALTER HELBLING ET AL.



a significantly higher concentration of UV-absorbing compounds when individuals

were feeding on the Rhodophyte Polysiphonia sp. than when they were feeding on

Chlorophytes. In A. valida (Fig. 6b), there was also an increase in the optical density

at 334 nm, being low when the organisms were feeding on Enteromorpha sp. and

significantly higher when they were feeding on Polysiphonia sp. Moreover, a higher

concentration of UV-absorbing compounds was found in A. valida compared with

that in I. baltica when feeding on Polysiphonia sp. This situation, however, was

reversed when the two crustacean species were collected from Chlorophyte species.

Survival experiments carried out with both species of crustaceans indicated a different ecological role of these compounds. In A. valida, and since a significant higher

survival was observed when organisms were feeding on Rhodophytes compared

with Chlorophytes, MAAs seem to provide an effective protection against UV-B

radiation. In I. baltica, however, mortality was high and not significantly different in

individuals feeding on rich and poor MAA diets. However, high amounts of MAAs

in eggs/embryos of I. baltica suggested that these compounds might provide protection to the progeny rather than to adults.

7. Conclusions

The results of the in situ experiments summarized above indicate that the studied

macroalgae are shade plants adapted to low light conditions during high tide

favored by strong absorption and scattering of solar radiation in the water column.

However, during low tide, organisms are damaged by high solar radiation exposure. Any further increase in solar UVR – for example, due to the continue decrease

of the stratospheric ozone layer or the extent of influence of the Antarctic ozone

‘hole’ over Patagonia – would worsen this situation, leading to more inhibition

of the algae. However, and so far, the studies have shown that the thalli protect

themselves by actively shutting down the photosynthetic electron transport to

recover during the subsequent low light phase. It is obvious that different species

are adapted to different heights on the coast, and it can be concluded that the

duration and intensity of solar radiation is a decisive factor in the habitat zonation

of macroalgae in the Patagonian region.



8. Acknowledgments

This work was supported by Agencia Nacional de Promoción Científica y Tecnológica

– ANPCyT (Project PICT N° 2005-32034 to VEV), Proalar (Project N° 2000-104 to EWH),

the United Nations Global Environmental Fund (PNUD Project N° B-C-39 to EWH),

Fundación Antorchas (Project A-13955/3 to EWH), the Deutsche Akademische

Austauschdienst (Project Proalar N° T332 408 138 415-RA to D.-P.H), and Fundación

Playa Unión. This is contribution N° 114 of Estación de Fotobiología Playa Unión.



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

 Presence and Dynamics of UVR-Absorbing Compounds in Patagonian Macroalgae

Tải bản đầy đủ ngay(0 tr)

×