Differences between sun (E) and shaded (S) foliage were studied in a Norway spruce (Picea abies [L.] Karst.) stand. Response curves describing the dependence of the CO2 assimilation rate (PN) on the CO2 concentration at the catalytic site of ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO (PN-Cc) were estimated using the simultaneous measurements of chlorophyll fluorescence and leaf gas exchange. Higher PN, higher electron transport (Ja), higher carboxylation capacity (Vc), and higher RuBPCO activity (τ) for sun acclimated needles was found. The S-needles had higher portion of internal limitation and higher CO2 compensation concentration (Γ) than the E-needles. Because higher degree of limitation of photosynthesis by carboxylation was ascertained, it can be assumed that photosynthesis in shade foliage is limited mainly by lower carboxylation capacity and by low chloroplastic CO2 concentration. and I. Priwitzer ... [et al.].
Changes in chloroplastidic pigments, gas exchange and carbohydrate concentrations were assessed during the rapid initial expansion of C. guianensis leaflet. Leaves at metaphyll stage were tagged and assessments were carried out 14, 17, 20, 23, 27, and 31 days later. Pigments synthesis, distribution and accumulation were uniform among leaflet sections (basal, median and apical). Chlorophyll (Chl) a, Chl b, Chl (a+b), and total carotenoids (Car) concentrations were significantly increased after 27 days from metaphyll, and the most expressive increases were parallel to lower specific leaflet area. Chl a/b was lower on day 14 and it was increased on subsequent days. Negative net photosynthesis rate (PN), and the lowest stomatal conductance (gs) and transpiration (E) were registered on day 14, following significant increases on subsequent days. The Chl (a+b) and Chl a effects on PN were more expressive until day 20. Intercellular to ambient CO2 concentration ratio (Ci/Ca) was higher on day 14 and lower on subsequent days, and no stomatal limitation to CO2 influx inside leaflets was observed. Leaflet temperature was almost constant (ca. 35°C) during leaflet development. Sucrose and starch concentrations were increased in parallel to increases in PN. Altogether, these results highlight the main physiological changes during C. guianensis leaflet expansion and they should be considered in future experiments focusing on factors affecting PN in this species. and F. K. C. Moraes ... [et al.].
The addition of chymostatin (100 mg m'^) to the extraction and desalting media for phosphoenolpyruvate carboxylase (EC 4.1.1.31) from Zea mays L. and Setaria verticillata (L.) Beauv. (C4-plants) affected profoundly the kinetics of the enzymic activity, the rate curve became considerably more sigmoid than that of the control and, therefore, the activity at low phosphoenolpyruvate levels was much reduced. Also, the sensitivity towards malate inhibition was substantially increased in both the day and night forms of the enzyme. The above effects were observed at pH 7.0, but not at pH 8.0. Glucose-6-phosphate (5 mM in extraction and desalting media) partly counteracted the effect of chymostatin on malate sensitivity. Hence chymostatin affected directly or indirectly the enzymic dimer/tetramer equilibrium in favour of the dimer.The addition of chymostatin (100 mg m'^) to the extraction and desalting media for phosphoenolpyruvate carboxylase (EC 4.1.1.31) from Zea mays L. and Setaria verticillata (L.) Beauv. (C4-plants) affected profoundly the kinetics of the enzymic activity, the rate curve became considerably more sigmoid than that of the control and, therefore, the activity at low phosphoenolpyruvate levels was much reduced. Also, the sensitivity towards malate inhibition was substantially increased in both the day and night forms of the enzyme. The above effects were observed at pH 7.0, but not at pH 8.0. Glucose-6-phosphate (5 mM in extraction and desalting media) partly counteracted the effect of chymostatin on malate sensitivity. Hence chymostatin affected directly or indirectly the enzymic dimer/tetramer equilibrium in favour of the dimer.
The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (PN) and its relative dependence on stomatal conductance (gs) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in PN measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO2 assimilation (φc) calculated from the PN/PFD response curves showed significant variations among the clones. PN at low irradiance was positively correlated with φc. Thus a clone with large PN at low irradiance, high φc, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between PN saturated with radiant energy (Psat) and carboxylation efficiency (CE) estimated from the response curves of PN on intercellular CO2 concentration (Ci), but gs showed a poor correlation with Psat High CO2 compensation concentration (Γ) led to low CE in Hevea clones. A clone with large Psat, high CE, low gs, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. and K. N. Nataraja, J. Jacob.
Fifty-d-old poplar (Populus deltoides L.) plants were irrigated with 50-200 mM NaCl. 100 and 200 mM NaCl significantly reduced net photosynthetic rate, chlorophyll and carotenoid contents, leaf area, dry matter accumulation, and harvest index (HI) in all tested poplar clones (Bahar, S7C15, and WSL22). Clone S7C15 was more tolerant to salinity than the other clones. and M. Singh, M. Jain, R. C. Pant.
Among the three cultívars of tea, Assam hybrids had a relatively higher net photosynthetic rate (P^) than the China and Cambod types. Though the leaves selected for chlorophyll (Chl) estimation were physiologically mature and identical, wide range of shades in the colour of leaves was observed. No significant difference between cultívars was notíced in Chl (a + b) content, but distinct difference was obtained among certain dones. Chl atb ratío exhibited significant difference between both the cultívars and dones.
Photosynthesis, photorespiration, and chlorophyll (Chl) fluorescence in green and red Berberis thunbergii leaves were studied with two different measuring radiations, red (RR) and "white" (WR). The photosynthetic and photorespiration rates responded differently to the different radiation qualities, which indicate that the carboxylase and oxygenase activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were affected. Differences in photosynthetic rate between the two color leaves were less under RR than under WR. However, this reduced difference in photosynthetic rate was not correlated with the stomatal response to the measuring radiation qualities. Compared with the WR, the RR reduced the differences in dark-adapted minimum and maximum fluorescence, steady-state fluorescence, light-adapted maximum fluorescence, and actual photochemical efficiency (ΦPS2) of photosystem 2 (PS2), but enlarged the difference in non-photochemical quenching between the two color leaves. Differences in both maximum quantum yield of PS2 and ratio of ΦPS2 to quantum yield of CO2 fixation between the two color leaves were similar under the two measuring radiations. To exclude disturbance of radiation attenuation caused by anthocyanins, it is better to use RR to compare the photosynthesis and Chl fluorescence in green versus red leaves. and P.-M. Li ... [et al.].
Gas exchanges and leaf water potential (Ψw) of six-years-old trees of fourteen Prunus amygdalus cultivars, grafted on GF-677, were studied in May, when fruits were in active growing period, and in October, after harvesting. The trees were grown in the field under rain fed conditions. Predawn Ψw showed lower water availability in October compared with May. The lowest Ψw values at midday in May increased gradually afterwards, while in October they decreased progressively until night, suggesting a higher difficulty to compensate the water lost by transpiration. However, relative water content (RWC) measured in the morning was similar in both periods, most likely due to some rainfall that occurred in September and first days of October that could be enough to re-hydrate canopy without significantly increasing soil water availability. The highest net photosynthetic rate (PN) was found in both periods early in the morning (08:00-11:00). Reductions in PN from May to October occurred in most cultivars except in José Dias and Ferrastar. In all cultivars a decrease in stomatal conductance (gs) was observed. Photosynthetic capacity (Pmax) did not significantly change from spring to autumn in nine cultivars, revealing a high resistance of photosynthetic machinery of this species to environmental stresses, namely high temperature and drought. Osmotic adjustment was observed in some cultivars, which showed reductions of ca. 23 % (Duro d' Estrada, José Dias) and 15 % (Tuono) in leaf osmotic potential (Ψπ). Such decreases were accompanied by soluble sugars accumulation. The Portuguese cultivar José Dias had a higher photosynthetic performance than the remaining genotypes. and M. C. Matos ... [et al.].