Crassulacean acid metabolism photosynthesis: ‘working the night shift’

Abstract

Crassulacean acid metabolism (CAM) can be traced from Roman times through persons who noted a morning acid taste of some common house plants. From India in 1815, Benjamin-Heyne described a 'daily acid taste cycle' with some succulent garden plants. Recent work has shown that the nocturnally formed acid is decarboxylated during the day to become the CO 2 for photosynthesis. Thus, CAM photosynthesis extends over a 24-hour day using several daily interlocking cycles. To understand CAM photosynthesis, several landmark discoveries were made at the following times: daily reciprocal acid and carbohydrate cycles were found during 1870 to 1887; their precise identification, as malic acid and starch, and accurate quantification occurred from 1940 to 1954; diffusive gas resistance methods were introduced in the early 1960s that led to understanding the powerful stomatal control of daily gas exchanges; C 4 photosynthesis in two different types of cells was discovered from 1965 to ∼1974 and the resultant information was used to elucidate the day and night portions of CAM photosynthesis in one cell; and exceptionally high internal green tissue CO 2 levels, 0.2 to 2.5%, upon the daytime decarboxylation of malic acid, were discovered in 1979. These discoveries then were combined with related information from C 3 and C 4 photosynthesis, carbon biochemistry, cellular anatomy, and ecological physiology. Therefore by ∼1980, CAM photosynthesis finally was rigorously outlined. In a nutshell, 24-hour CAM occurs by phosphoenol pyruvate (PEP) carboxylase fixing CO 2 (HCO 3 − ) over the night to form malic acid that is stored in plant cell vacuoles. While stomata are tightly closed the following day, malic acid is decarboxylated releasing CO 2 for C 3 photosynthesis via ribulose bisphosphate carboxylase oxygenase (Rubisco). The CO 2 acceptor, PEP, is formed via glycolysis at night from starch or other stored carbohydrates and after decarboxylation the three carbons are restored each day. In mid to late afternoon the stomata can open and mostly C 3 photosynthesis occurs until darkness. CAM photosynthesis can be both inducible and constitutive and is known in 33 families with an estimated 15 to 20 000 species. CAM plants express the most plastic and tenacious photosynthesis known in that they can switch photosynthesis pathways and they can live and conduct photosynthesis for years even in the virtual absence of external H 2 O and CO 2 , i.e., CAM tenaciously protects its photosynthesis from both H 2 O and CO 2 stresses.Abbreviations: CAM -Crassulacean acid metabolism; PEP -phosphoenol-pyruvate; Rubisco -ribulose 1,5-bisphosphate carboxylase oxygenase; C 3 -three carbon photosynthesis; C 4 -four carbon photosynthesis; PEPCase -phosphoenol pyruvate carboxylase 330

The effects of salinity, crassulacean acid metabolism and plant age on the carbon isotope composition of Mesembryanthemum crystallinum L., a halophytic C3-CAM species

“…PEPC, which is responsible for CO 2 uptake at night, discriminates less against 13 CO 2 than does ribulosebisphosphate carboxylase/oxygenase (Rubisco) which is responsible for the bulk of the CO 2 fixed during the light. As a result, plants with pronounced CAM exhibit less negative d 13 C values than C 3 plants do (Griffiths 1992;Black and Osmond 2003).…”

Environment or Development? Lifetime Net CO2 Exchange and Control of the Expression of Crassulacean Acid Metabolism inMesembryanthemum crystallinum

“…Since then, there have been frequent reports of some CAM activity in well-watered, non-salt-treated mature to old plants (e.g. Cushman et al, 1990) and M. crystallinum is now commonly described in the literature as ''a halophyte with a developmentally programmed switch from C 3 photosynthesis to CAM which is accelerated by salinity and drought'' (p. 171; Adams et al, 1998; see also Herppich et al, 1992;Cushman, 2001;Yen et al, 2001;Cushman and Bohnert, 2002;Cushman and Borland, 2002;Grams and Thiel, 2002;Black and Osmond, 2003;Dodd et al, 2003;Popp et al, 2003;Trofimova et al, 2003;Berg et al, 2004;Bozhko et al, 2004;Hurst et al, 2004;Libik et al, 2004;Lü ttge, 2004;Niewiadomska et al, 2004).…”

Berger C. Mayne (1920–2011): a friend and his contributions to photosynthesis research

“…In the 1960s, biochemist Clanton Black (1931Black ( -2011; see a minireview by Black and Osmond 2005) and an agronomist Harold Brown at the University of Georgia had an interest in knowing differences in the efficiency of photosynthesis in crops and weedy species. They published a paper in Weed Science on the competitive ability of plants with respect to photosynthesis, based on reported differences in physiological features and emerging information on plants having a C 4 cycle (Black et al 1969).…”