TY - JOUR
T1 - Carbon metabolism in seagrasses
T2 - II. Patterns of photos ynthetic co2 incorporation
AU - Beer, Sven
AU - Shomer-ilan, Adiva
AU - Waisel, Yoav
PY - 1980/8
Y1 - 1980/8
N2 - Patterns of initial photosynthetic CO2 incorporation were determined for some seagrasses and were related to activities of primary carbon fixing enzymes, carbonic anhydrase activities, and δ13C values.According to the incorporation patterns, Cymodocea nodosa was a C4 species while Thalassia hemprichli and Thalassodendron ciliatum were C3 plants. Halophila stipulacea showed an unusual incorporation pattern which could be viewed as intermediate between typical C3 and C4 pathways. The activity ratios of ribulose-l, 5-bisphosphate carboxylase (RUBPcase) to phosphoenolpyruvate carboxylase (PEPcase) were about 3 for Thalassodendron ciliatum and 1 for Cymodocea nodosa and Halophila stipulacea. The latter value, which is intermediate to ratios found in terrestrial C3 and C4 plants, may correlate with the incorporation patterns found for Halophila stipulacea. Since the C4 seagrass lacked the Kranz anatomy, it may, in addition, point to a flexible incorporation potential for these plants.The high δ13C values found in these and other seagrasses did not correlate with their photosynthetic pathways as in terrestrial plants. This discrepancy is probably due to a 'closed system' type of photosynthesis in which CO2 is efficiently utilized.The C3 species which utilize CO2 enzymatically must convert exogenous HCO-3 to CO2 internally. Even though carbonic anhydrase activities were very low, conversion rates seemed to be sufficient for high rates of photosynthesis. Since enzymatic fixation rates approached photosynthetic rates even at CO2 saturation, the limitation for these seagrasses to express their high photosynthetic potential is most probably the HCO-3 uptake system.
AB - Patterns of initial photosynthetic CO2 incorporation were determined for some seagrasses and were related to activities of primary carbon fixing enzymes, carbonic anhydrase activities, and δ13C values.According to the incorporation patterns, Cymodocea nodosa was a C4 species while Thalassia hemprichli and Thalassodendron ciliatum were C3 plants. Halophila stipulacea showed an unusual incorporation pattern which could be viewed as intermediate between typical C3 and C4 pathways. The activity ratios of ribulose-l, 5-bisphosphate carboxylase (RUBPcase) to phosphoenolpyruvate carboxylase (PEPcase) were about 3 for Thalassodendron ciliatum and 1 for Cymodocea nodosa and Halophila stipulacea. The latter value, which is intermediate to ratios found in terrestrial C3 and C4 plants, may correlate with the incorporation patterns found for Halophila stipulacea. Since the C4 seagrass lacked the Kranz anatomy, it may, in addition, point to a flexible incorporation potential for these plants.The high δ13C values found in these and other seagrasses did not correlate with their photosynthetic pathways as in terrestrial plants. This discrepancy is probably due to a 'closed system' type of photosynthesis in which CO2 is efficiently utilized.The C3 species which utilize CO2 enzymatically must convert exogenous HCO-3 to CO2 internally. Even though carbonic anhydrase activities were very low, conversion rates seemed to be sufficient for high rates of photosynthesis. Since enzymatic fixation rates approached photosynthetic rates even at CO2 saturation, the limitation for these seagrasses to express their high photosynthetic potential is most probably the HCO-3 uptake system.
UR - http://www.scopus.com/inward/record.url?scp=0001545333&partnerID=8YFLogxK
U2 - 10.1093/jxb/31.4.1019
DO - 10.1093/jxb/31.4.1019
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AN - SCOPUS:0001545333
SN - 0022-0957
VL - 31
SP - 1019
EP - 1026
JO - Journal of Experimental Botany
JF - Journal of Experimental Botany
IS - 4
ER -