Photosynthetic Characteristics of the C3-C4 Intermediate Parthenium hysterophorus
- 1 December 1987
- journal article
- research article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 85 (4) , 978-983
- https://doi.org/10.1104/pp.85.4.978
Abstract
The weedy species Parthenium hysterophorus (Asteraceae) possesses a Kranz-like leaf anatomy. The bundle sheath cells are thick-walled and contain numerous granal chloroplasts, prominent mitochondria, and peroxisomes, all largerly arranged in a centripetal position. Both mesophyll and bundle sheath chloroplasts accumulate starch. P. hysterophorus exhibits reduced photorespiration as indicated by a moderately low CO2 compensation concentration (20-25 microliters per liter at 30.degree.C and 21% O2) and by a reduced sensitivity of net photosynthesis to 21% O2. In contrast, the related C3 species P. incanum and P. argentatum (guayule) lack Kranz anatomy, have higher CO2 compensation concentrations (about 55 microliters per liter), and show a greater inhibition of photosynthesis by 21% O2. Furthermore, in P. hysterophorus the CO2 compensation concentration is relatively less sensitive to changes in O2 concentrations and shows a biphasic response to changing O2, with a transition point at about 11% O2. Based on these results, P. hysterophorus is classified as a C3-C4 intermediate. The activities of diagnostic enzymes of C4 photosynthesis in P. hysterophorus were very low, comparable to those observed in the C3 species P. incanum (e.g. phosphoenolypyruvate carboxylase activity of 10-29 micromoles per milligram of chlorophyll per hour). Exposures of leaves of each species to 14CO2 (for 8 seconds) in the light resulted in 3-phosphoglycerate and sugar phosphates being the predominant initial 14C products (77-84%), with .ltoreq. 4% of the 14C-label in malate plus aspartate. These results indicate that in the C3-C4 intermediate P. hysterophorus, the reduction in leaf photorespiration cannot be attributed to C4 photosynthesis.This publication has 20 references indexed in Scilit:
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