Thylakoid membranes (TM) of the cyanobacterium Synechococcus elongatus were exposed for 30 min to the influence of 0, 10, 100, and 1 000 mM CdCl2 (= Cd0, Cd10, Cd100, and Cd1000). Cd10 and Cd100 caused some increase in activity of photosystem 2, PS2 (H2O → DCPIP), while distinct inhibition was observed with Cd1000. We also observed a similar effect when measuring oxygen evolution (H2O → PBQ + FeCy). Chloroplasts of spinach (Spinacia oleracea L.) were incubated for 30 min with 0, 15, 30, and 60 mM CdCl2 (= Cd0, Cd15, Cd30, and Cd60). All concentrations studied inhibited the PS2 activity, the effect being stronger with increasing concentration of Cd2+. The photosynthetic oxygen evolution activity was also influenced most distinctly by the highest concentration employed, i.e. Cd60. Electrophoretic analysis of the protein composition of cyanobacterium TM showed chief changes in the molecular mass regions of Mr 29 000 and 116 000, while with spinach chloroplasts the most distinct differences were observed in the regions of Mr 15 000 and 50 000. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity in cyanobacterial spheroplasts still remained on the 40 % level in the case of Cd1000, but it decreased down to approx. 2.5 % in the Cd60 sample of spinach chloroplasts. and M. Nováková, E. Matějová, D. Sofrová.
A field experiment was conducted to investigate the changes in chlorophyll (Chl) and nitrogen (N) contents, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) contents and PEPC activity, and the photon-saturated net photosynthetic rate (PNsat), and their relationships with leaf senescence in two maize hybrids with different senescent appearance. One stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55) hybrid were used in this study, and we found that Chl and N contents and the PNsat in individual leaves of P3845 were greater than those in corresponding leaves of Hokkou 55 at the successive growth stages. In addition, larger contents of RuBPCO and PEPC, and a greater activity of PEPC were observed in P3845. Due to the lower rates of decrease of Chl, RuBPCO, and PEPC amounts per unit of N, and the lower net C translocation rate per unit of N in the stay-green hybrid, leaf senescence was delayed in comparison to the earlier senescent hybrid. and Ping He ... [et al.].
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.].
Leaves developed at high irradiance (I) often have higher photosynthetic capacity than those developed at low I, while leaves developed at elevated CO2 concentration [CO2] often have reduced photosynthetic capacity compared with leaves developed at lower [CO2]. Because both high I and elevated [CO2] stimulate photosynthesis of developing leaves, their contrasting effects on photosynthetic capacity at maturity suggest that the extra photosynthate may be utilized differently depending on whether I or [CO2] stimulates photosynthesis. These experiments were designed to test whether relationships between photosynthetic income and the net accumulation of soluble protein in developing leaves, or relationships between soluble protein and photosynthetic capacity at full expansion differed depending on whether I or [CO2] was varied during leaf development. Soybean plants were grown initially with a photosynthetic photon flux density (PPFD) of 950 µmol m-2 s-1 and 350 µmol [CO2] mol-1, then exposed to [CO2] ranging from 135 to 1400 µmol mol-1 for the last 3 d of expansion of third trifoliolate leaves. These results were compared with experiments in which I was varied at a constant [CO2] of 350 µmol mol-1 over the same developmental period. Increases in area and dry mass over the 3 d were determined along with daily photosynthesis and respiration. Photosynthetic CO2 exchange characteristics and soluble protein content of leaves were determined at the end of the treatment periods. The increase in leaflet mass was about 28 % of the dry mass income from photosynthesis minus respiration, regardless of whether [CO2] or I was varied, except that very low I or [CO2] increased this percentage. Leaflet soluble protein per unit of area at full expansion had the same positive linear relationship to photosynthetic income whether [CO2] or I was varied. For variation in I, photosynthetic capacity varied directly with soluble protein per unit area. This was not the case for variation in [CO2]. Increasing [CO2] reduced photosynthetic capacity per unit of soluble protein by up to a factor of 2.5, and photosynthetic capacity exhibited an optimum with respect to growth [CO2]. Thus CO2 did not alter the relationship between photosynthetic income and the utilization of photosynthate in the net accumulation of soluble protein, but did alter the relationship between soluble protein content and photosynthetic characteristics in this species.
Gas exchange, chlorophyll (Chl) fluorescence, and contents of photosynthetic pigments, soluble proteins (ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO), and antioxidant enzymes were characterized in the fully expanded 6th leaves in rice seedlings grown on either complete (CK) or on nitrogen-deficient nutrient (N-deficiency) solutions during a 20-chase period. Compared with the control plants, the lower photosynthetic capacity at saturation irradiance (Pmax) was accompanied by an increase in intercellular CO2 concentration (Ci), indicating that in N-deficient plants the decline in Pmax was not due to stomatal limitation but due to the reduced carboxylation efficiency. The fluorescence parameters ΦPS2, Fv'/Fm', electron transport rate (ETR), and qP showed the same tendency as Pmax in N-deficient plants. Correspondingly, a higher qN paralleled the rise of the ratio of carotenoid (Car) to Chl contents. However, Fv/Fm was still diminished, suggesting that photoinhibition did occur in the photosystem 2 (PS2) reaction centres. In addition, the activities of antioxidant enzymes on a fresh mass basis were gradually lowered, leading to the aggravation of membrane lipid peroxidation with the proceeding N-deficiency. The accumulation of malonyldialdehyde resulted in the lessening of Chl and soluble protein content. Analyses of regression showed PS2 excitation pressure (1 - qP) was linearly correlated with the content of Chl and inversely with soluble protein (particularly RuBPCO) content. There was a lag phase in the increase of PS2 excitation pressure compared to the decrease of RuBPCO content. Therefore, the increased excitation pressure under N-deficiency is probably the result of saturation of the electron transport chain due to the limitation of the use of reductants by the Calvin cycle. Rice plants responded to N-deficiency and high irradiance by decreasing light-harvesting capacity and by increasing thermal dissipation of absorbed energy. and Z.-A. Huang ... [et al.].
Activities of ribulose bisphosphate carboxylase/oxygenase (RuBPCO), phosphoenolpyruvate carboxylase (PEPC), and carbonic anhydrase (CA) were determined in leaves of cotton (Gossypium hirsutum L. cv. H-777) subjected to 8-d waterlogging (WL) at the vegetative stage, or to drought (D) at the reproductive stage, or to interaction of both stresses. The soil moisture of control plants was kept at field capacity. One day prior to stress various growth hormones (5 μM) were sprayed up to runoff. WL reduced RuBPCO and CA activities, while PEPC activity increased. Upon D, RuBPCO and PEPC activities were reduced while CA activity was increased. Imposition of both stresses increased activities of all three enzymes. Effect of stresses on enzyme activity was alleviated by benzylaminopurine (BAP), but indol-3-yl-acetic acid was more promoting under interactive stress. No CA activity with BAP was observed during interactive stress. and D. M. Pandey ... [et al.].
Steady state transcript levels of psbA, rbcL, atpB, and psbN genes accumulated differentially in mature leaves of a field-grown tree Populus deltoides during natural diurnal cycle and in dark adaptation followed by irradiation. The rbcL transcript accumulated independent of irradiation under diurnal conditions, which demonstrated a correlation with the phenomenon of midday depression in photosynthesis. The psbA and atpB transcripts accumulated more in dark whereas psbN accumulated more in light. Diurnal rhythm of gene expression in mature chloroplasts was independent of development related changes. and S. Srivastava, P. K. Trivedi, P. Nath.
The photosynthetic response of three Arachis hypogaea L. cultivars (57-422, 73-30, and GC 8-35) grown for two months was measured under water available conditions, severe water stress, and 24, 72, and 93 h following re-watering. At the end of the drying cycle, all the cultivars reached dehydration, relative water content (RWC) ranging between 40 and 50 %. During dehydration, leaf stomatal conductance (gs), transpiration rate (E), and net photosynthetic rate (PN) decreased more in cvs. 57-422 and GC 8-35 than in 73-30. Instantaneous water use efficiency (WUEi) and photosynthetic capacity (Pmax) decreased mostly in cv. GC 8-35. Except in cv. GC 8-35, the activity of photosystem 1 (PS1) was only slightly affected. PS2 and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were the main targets of water stress. After re-watering, cvs. 73-30 and GC 8-35 rapidly regained gs, E, and PN activities. Twenty-four hours after re-watering, the electron transport rates and RuBPCO activity strongly increased. PN and Pmax fully recovered later. Considering the different photosynthetic responses of the studied genotype, a general characterisation of the interaction between water stress and this metabolism is presented. and J. A. Lauriano ... [et al.].
We studied the responses of leaf gas exchange and growth to an increase in atmospheric CO2 concentration in four tropical deciduous species differing in carbon fixation metabolism: Alternanthera crucis, C3-C4; Ipomoea carnea, C3; Jatropha gossypifolia, C3; and Talinum triangulare, inducible-CAM. In the first stage, plants were grown in one open-top chamber at a CO2 concentration of 560±40 μmol mol-1 (EC), one ambient CO2 concentration chamber (AC), and one unenclosed plot (U). In the second stage, plants were grown in five EC chambers (CO2 concentration = 680±30 μmol mol-1), five AC chambers, and five unenclosed plots. During the first weeks under EC in the first stage, plants of all the species had a very marked increase in their maximal net photosynthetic rates (Pmax) of 3.5 times on average; this stimulatory effect was maintained for 11-15 weeks, rates dampening afterward to values still higher than controls for 37 weeks. After a suspension of CO2 enrichment for 6 weeks, an increase in Pmax of EC plants over the controls was found in plants of all the species until week 82 of the experiment. Stomatal conductance (g) showed no response to EC. Carboxylation efficiency decreased in all the species under EC and this was correlated with a decrease in ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) content in all the species except for T. triangulare. During drought Pmax was higher in all species except for 7 triangulare, grown under EC relative to controls.
Ecosystem photosynthetic rates at EC were higher than in the controls during the second stage under irrigation as well as after 30 d of drought. and M. D. Fernández ... [et al.].
Chlorophyll content, photosystem 2 functioning (Fv/Fm, Fv/F0), activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, and net photosynthetic rates (PN) of flag leaf blade, sheath, peduncle, and ear organs were assessed in large-ear type (Pin 7) and small-ear type (ND93) wheat cultivars. Some differences were found in photosynthetic properties between different green plant parts, the values of all studied parameters in ear parts being higher in Pin7 than in ND93. Furthermore, ear surface areas and ear PN in 26 wheat genotypes measured at anthesis showed highly significant positive correlation with grain mass per ear. Hence a greater capability of ear photosynthesis may result in a greater grain yield in large-ear type cultivars. and Zhi-Min Wang, Ai-Li Wei, Dan-Man Zheng.