The metabolic pathway of primary carbon fixation was studied in a peculiar pennate marine diatom, Haslea ostrearia (Bory) Simonsen, which synthesizes and accumulates a blue pigment known as "marennine". Cells were cultured in a semi-continuous mode under saturating [350 µmol(photon) m-2 s-1] or non-saturating [25 µmol(photon) m-2 s-1] irradiance producing "blue" (BC) and "green" (GC) cells, characterized by high and low marennine accumulation, respectively. Growth, pigment contents (chlorophyll a and marennine), 14C accumulation in the metabolites, and the carbonic anhydrase (CA) activity of the cells were determined during the exponential growth phase. Growth rate and marennine content were closely linked to irradiance during growth: higher irradiance increased both growth rate and marennine content. On the other hand, the Chl a concentration was lower under saturating irradiance. The distribution between the Calvin-Benson (C3) and β-carboxylation (C4) pathways was very different depending on the irradiance during growth. Metabolites of the C3 cycle contained about 70 % of the total fixed radioactivity after 60 s of incorporation into cells cultured under the non-saturating irradiance (GC), but only 47 % under saturating irradiance (BC). At the same time, carbon fixation by β-carboxylation was 24 % in GC versus about 41 % in BC, becoming equal to that in the C3 fixation pathway in the latter. Internal CA activity remained constant, but the periplasmic CA activity was higher under low than high irradiance. and M. Rech, A. Morant-Manceau, G. Tremblin.
Despite the elimination of the original forest and frequent cultivation using slash and burn, a large spread in leaf δ13C was recorded in weeds, crops, and bush fallow species, reflecting a forest environment rather than a broken canopy or open environment., A. De Rouw, J .F. Maxwell, C. Girardin., and Obsahuje bibliografii
Spartina maritima (Curtis) Fernald, Spartina densiflora Brong, Arthrocnemum perenne (Miller) Moss, and Arthrocnemum fruticosum (L.) Moq are very frequent halophytes on the coasts of SW Europe. The first two are perennial Gramineae with C4 metabolism; the last two are perennial Chenopodiaceae with C3 metabolism. Controlled garden experiments were carried out with the four species to compare their physiological response, i.e., water potential (Ψ), net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), and chlorophyll fluorescence of photosystem (PS) 2 under saline and non-saline conditions. S. maritima behaves as an osmoconformer species, the other three as osmoregulators. In the four species, PN, E, and gs improved following freshwater irrigation. The variations in PN might be related with biochemical changes (which appear not to affect PS2), but not with significant stomatal fluctuations, which are associated with a lower water use efficiency in the case of Arthrocnemum. The species were segregated into two groups (not depending on their C3 or C4 photosynthetic pathway), in relation with the topographic level of this species in natural conditions: the relative responses of PN in S. maritima and A. perenne were lower than those of S. densiflora and A. fruticosum. The salt-tolerance index supports such segregation. S. densiflora demonstrated the best competitive possibilities against salt-tolerant glycophytes, with its more flexible response in saline or brackish environments, which explains its spreading along the rivers draining into the estuaries of the SW Iberian Peninsula. and F. J. J. Nieva ... [et al.].
Biao 810S is a chlorina mutant of the thermosensitive genic male sterile (TGMS) rice. We compared photosynthetic characteristics of these two lines. The contents of chlorophylls and carotenoids in Biao 810S were approximately half of those in 810S. However, the net photosynthetic rate (PN) of Biao 810S was higher than that of 810S under high irradiance or low concentration of carbon dioxide, and the photon quantum efficiency was higher than that of 810S. The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in Biao 810S was only 69.80 % of that in 810S, but the activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme were 79.50 and 69.06 % higher than those of 810S, respectively, suggesting that the efficiency of photon energy utilization in Biao 810S was enhanced by reduction of thermal dissipation and increase of electron transfer rate to generate sufficient assimilation power for the dark reactions. Consequently, the increased activities of C4 photosynthetic enzymes lead to more effective fixation of CO2 and the synergistic effect of light and dark reactions contributed to the higher PN of Biao 810S. and L.-J. Ou ... [et al.].
In order to determine whether stomatal closure alone regulates photosynthesis during drought under natural conditions, seasonal changes in leaf gas exchange were studied in plants of five species differing in life form and carbon fixation pathway growing in a thorn scrub in Venezuela. The species were: Ipomoea carnea, Jatropha gossypifolia, (C3 deciduous shrubs), Alternanthera crucis (C4 deciduous herb), and Prosopis juliflora and Capparis odoratissima (evergreen phreatophytic trees). Xylem water potential (Ψ) of all species followed very roughly the precipitation pattern, being more closely governed by soil water content in I. carnea and A. crucis. Maximum rate of photosynthesis, Pmax, decreased with Ψ in I. carnea, J. gossypifolia, and A. crucis. In I. carnea and J. gossypifolia stomatal closure was responsible for a 90 % decline in net photosynthetic rate (PN) as Ψ decreased from -0.3 to -2.0 MPa, since stomatal conductance (gs) was sensitive to water stress, and stomatal limitation on PN increased with drought. In A. crucis, PN decreased by 90 % at a much lower Ψ (-9.3 MPa), and gs was relatively less sensitive to Ψ. In P. juliflora and C. odoratissima, Pmax, gs, and intercellular CO2 concentration (Ci) were independent of soil water content. In the C3 shrubs stomatal closure was apparently the main constraint on photosynthesis during drought, Ci declining with Ψ in I. carnea. In the C4 herb, Ci was constant along the range of Ψ values, which suggested a coordinated decrease in both gs and mesophyll capacity. In P. juliflora Ci showed a slow decrease with Ψ which may have been due to seasonal leaf developmental changes, rather than to soil water availability. and W. Tezara ... [et al.].