Editing Photosynthesis (section)

===C3 : C4 photosynthesis research===
In the late 1940s at the [[University of California, Berkeley]], the details of photosynthetic carbon metabolism were sorted out by the chemists [[Melvin Calvin]], Andrew Benson, James Bassham and a score of students and researchers utilizing the carbon-14 isotope and paper chromatography techniques.<ref>{{cite journal |vauthors= Calvin M |title= Forty years of photosynthesis and related activities |journal= Photosynthesis Research |volume= 21 |issue= 1 |pages= 3–16 |date= July 1989 |bibcode= 1989PhoRe..21....3C |doi= 10.1007/BF00047170 |pmid= 24424488 |s2cid= 40443000 |name-list-style= vanc }}</ref> The pathway of CO<sub>2</sub> fixation by the algae ''Chlorella'' in a fraction of a second in light resulted in a three carbon molecule called phosphoglyceric acid (PGA). For that original and ground-breaking work, a [[Nobel Prize in Chemistry]] was awarded to Melvin Calvin in 1961. In parallel, plant physiologists studied leaf gas exchanges using the new method of infrared gas analysis and a leaf chamber where the net photosynthetic rates ranged from 10 to 13 μmol CO<sub>2</sub>·m<sup>−2</sup>·s<sup>−1</sup>, with the conclusion that all terrestrial plants have the same photosynthetic capacities, that are light saturated at less than 50% of sunlight.<ref>{{cite journal |vauthors= Verduin J |year= 1953 |title= A table of photosynthesis rates under optimal, near natural conditions. |journal= Am. J. Bot. |volume= 40 |issue= 9 |pages= 675–679 |doi=10.1002/j.1537-2197.1953.tb06540.x |jstor= 2439681 |bibcode= 1953AmJB...40..675V }}</ref><ref>{{cite journal |vauthors= Verduin J, Whitwer EE, Cowell BC |date= July 1959 |title= Maximal photosynthetic rates in nature |journal= Science |volume= 130 |issue= 3370 |pages= 268–269 |bibcode= 1959Sci...130..268V |doi= 10.1126/science.130.3370.268 |pmid= 13668557 |s2cid= 34122342 }}</ref>

Later in 1958–1963 at [[Cornell University]], field grown [[maize]] was reported to have much greater leaf photosynthetic rates of 40 μmol CO<sub>2</sub>·m<sup>−2</sup>·s<sup>−1</sup> and not be saturated at near full sunlight.<ref>{{cite journal |vauthors= Hesketh JD, Musgrave R |year= 1962 |title= Photosynthesis under field conditions. IV. Light studies with individual corn leaves |journal= Crop Sci. |volume= 2 |issue= 4 |pages= 311–315 |doi= 10.2135/cropsci1962.0011183x000200040011x |s2cid= 83706567 }}</ref><ref>{{cite journal |vauthors= Hesketh JD, Moss DN |year= 1963 |title= Variation in the response of photosynthesis to light |journal= Crop Sci. |volume= 3 |issue= 2 |pages= 107–110 |doi= 10.2135/cropsci1963.0011183X000300020002x }}</ref> This higher rate in maize was almost double of those observed in other species such as wheat and soybean, indicating that large differences in photosynthesis exist among higher plants. At the University of Arizona, detailed gas exchange research on more than 15 species of [[Monocotyledon|monocot]]s and [[Dicotyledon|dicot]]s uncovered for the first time that differences in leaf anatomy are crucial factors in differentiating photosynthetic capacities among species.<ref name="El-Sharkawy-1965">{{cite journal |vauthors= El-Sharkawy, MA, Hesketh JD |year= 1965 |title= Photosynthesis among species in relation to characteristics of leaf anatomy and CO<sub>2</sub> diffusion resistances |journal= Crop Sci. |volume= 5 |issue= 6 |pages= 517–521 |doi=10.2135/cropsci1965.0011183x000500060010x}}</ref><ref name="El-Sharkawy-1986">{{cite journal |vauthors= El-Sharkawy MA, Hesketh JD |year= 1986 |title= Citation Classic-Photosynthesis among species in relation to characteristics of leaf anatomy and CO<sub>2</sub> diffusion resistances |journal= Curr. Cont./Agr.Biol.Environ |volume= 27 |page= 14 |url= http://www.garfield.library.upenn.edu/classics1986/A1986C891300001.pdf |access-date= 2023-12-06 |archive-url= https://web.archive.org/web/20231129020950/http://www.garfield.library.upenn.edu/classics1986/A1986C891300001.pdf |archive-date= 2023-11-29 |url-status= dead }}</ref> In tropical grasses, including maize, sorghum, sugarcane, Bermuda grass and in the dicot amaranthus, leaf photosynthetic rates were around 38−40 μmol CO<sub>2</sub>·m<sup>−2</sup>·s<sup>−1</sup>, and the leaves have two types of green cells, i.e. outer layer of mesophyll cells surrounding a tightly packed cholorophyllous vascular bundle sheath cells. This type of anatomy was termed Kranz anatomy in the 19th century by the botanist [[Gottlieb Haberlandt]] while studying leaf anatomy of sugarcane.<ref>{{cite book |vauthors= Haberlandt G |year= 1904 |title= Physiologische Pflanzanatomie |publisher= Engelmann |location= Leipzig |url= https://books.google.com/books?id=6pk_AAAAYAAJ |access-date= 2019-04-17 |archive-date= 2023-01-19 |archive-url= https://web.archive.org/web/20230119181853/https://books.google.com/books?id=6pk_AAAAYAAJ |url-status= live }}</ref> Plant species with the greatest photosynthetic rates and Kranz anatomy showed no apparent photorespiration, very low CO<sub>2</sub> compensation point, high optimum temperature, high stomatal resistances and lower mesophyll resistances for gas diffusion and rates never saturated at full sun light.<ref>{{cite thesis |vauthors= El-Sharkawy MA |year= 1965 |title= Factors Limiting Photosynthetic Rates of Different Plant Species |degree= Ph.D. |publisher= The University of Arizona, Tucson}}</ref> The research at Arizona was designated a Citation Classic in 1986.<ref name="El-Sharkawy-1986"/> These species were later termed C4 plants as the first stable compound of CO<sub>2</sub> fixation in light has four carbons as malate and aspartate.<ref>{{cite journal |vauthors= Karpilov YS |year= 1960 |title= The distribution of radioactvity in carbon-14 among the products of photosynthesis in maize |journal= Proc. Kazan Agric. Inst. |volume= 14 |pages= 15–24 }}</ref><ref>{{cite journal |vauthors= Kortschak HP, Hart CE, Burr GO |year= 1965 |title= Carbon dioxide fixation in sugarcane leaves |journal= Plant Physiol |volume= 40 |issue= 2 |pages= 209–213 |doi= 10.1104/pp.40.2.209 |pmc= 550268 |pmid= 16656075 }}</ref><ref>{{cite journal |vauthors= Hatch MD, Slack CR |year= 1966 |title= Photosynthesis by sugar-cane leaves. A new carboxylation reaction and the pathway of sugar formation |journal= Biochem. J. |volume= 101 |issue= 1 |pages= 103–111 |doi= 10.1042/bj1010103 |pmc= 1270070 |pmid= 5971771 }}</ref> Other species that lack Kranz anatomy were termed C3 type such as cotton and sunflower, as the first stable carbon compound is the three-carbon PGA. At 1000 ppm CO<sub>2</sub> in measuring air, both the C3 and C4 plants had similar leaf photosynthetic rates around 60 μmol CO<sub>2</sub>·m<sup>−2</sup>·s<sup>−1</sup> indicating the suppression of photorespiration in C3 plants.<ref name="El-Sharkawy-1965"/><ref name="El-Sharkawy-1986"/>