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Photosynthetic Characteristics of Panicum milioides , a Species with Reduced Photorespiration 1
Author(s) -
Brown R. H.,
Brown W. V.
Publication year - 1975
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1975.0011183x001500050020x
Subject(s) - photorespiration , panicum , festuca arundinacea , biology , photosynthesis , botany , zoology , festuca , poaceae , horticulture
A species ( Panicum milioides Nees ex. Trin.), has been found which apparently has a reduced rate of photorespiration compared to other C 3 plants. It was found in preliminary studies that the response of net photosynthesis (Pn) to O 2 concentration was less for this species than for other C 3 plants. Therefore, this work was conducted to characterize for five accessions of P. milioides the CO 2 exchange related to photorespiration. Panicum maximum Jacq . (C 4 ), P. laevifolium Htack. (C 4 ), and tall fescue ( Festuca arundinacea Schreb. (C 3 ) were included for comparison. Leaf cross‐sections of P. milioides were examined for characteristics known to be related to photosynthetic carbon pathways. 13 C/ 12 C ratios were determined on P. milioides tissue. P. milioides photorespired less than tall fescue and more than P. maximum as determined by the three criteria: Pn response to O 2 , CO 2 evolution in the light, and CO 2 compensation concentration. The change in Pn for each 1% increase in O 2 was from −0.36 to −0.48 mg CO 2 dm −2 h −1 for five accessions of P. milioides compared to −0.10, −0.13, and −0.61 mg dm −2 h −1 for P. maximum , P. laevifolium , and tall fescue, respectively. P. milioides evolved an average of 0.85 mg CO 2 dm −2 h −1 in the light at 20% O 2 compared to 0.02 mg dm −2 h −1 for P. maximum and 2.96 mg dm −2 h −1 for tall fescue. CO 2 compensation concentrations determined by a Mylar bag technique were 0.4, 15.8, and 54 ppm for P. maximum , P. milioides , and tall fescue, respectively. Determination of CO 2 compensation from Pn response to CO 2 gave a similar trend, although actual concentrations were different. P. milioides tissue had δ 13 C values of about −25 ‰, characteristic of C 3 species. A leaf anatomical study showed that P. milioides had enlarged parenchyma sheath cells with centripetally located chloroplasts and mesophyll cells arranged in a radial manner around the parenchyma sheath. The parenchyma sheath cell walls appeared to be thicker than those of most C 3 species. It is concluded that while P. milioides exhibits mostly C 3 characteristics, its reduced photorespiration rate and some C 4 ‐like anatomical characteristics indicate a degree of intermediacy between C 3 and C 4 .