The effects of NaCl treatment on the photosynthetic machinery in wheat (Triticum aestivum L.) cultivars differing in salt tolerance were investigated by comparison with iso-osmotic PEG treatment. Both cultivars similarly reduced the photosystem 2 (PS2) energy conversion efficiency (ΦPS2) rapidly when plants were exposed to a 100 mM NaCl solution, though no decline was detected under the iso-osmotic PEG treatment. There was no correlation between the reduction of the leaf relative water content (RWC) and the ΦPS2 in the two iso-osmotic stress treatments. In contrast, a decline of ΦPS2 along with the increase of the leaf sodium content above 4 % dry matter was detected under the NaCl treatment, while no such correlation was detected with other cations. The recovery of ΦPS2 after photoinhibitory irradiation was repressed by the NaCl treatment as the increase of the duration of the treatment. Norin 61 subjected to the 100 mM NaCl treatment for 10 d showed a decline of the ΦPS2 after 1 h moderate irradiation of 400 μmol m-2 s-1 PPFD. Thus the concentrated Na+ within a leaf under salinity treatments may decrease the stability of PS2 functions and lead to photochemical inactivation. and S. Muranaka, K. Shimizu, M. Kato.
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.
The effects of iso-osmotic salinity and drought stresses on leaf net photosynthetic rate (PN) in two wheat (Triticum aestivum L.) cultivars BR 8 and Norin 61, differing in drought tolerance, were compared. In drought-sensitive Norin 61, the decline of PN was larger than that in drought-tolerant BR 8. Under NaCl treatment, PN decreased in two phases similarly in both cultivars. In the first phase, photosynthetic depression was gradual without any photochemical changes. In the second phase, photosynthetic depression was rapid and accompanied with a decline of the energy conversion efficiency in photosystem 2 (ΦPS2). Our observations suggest that the osmotic factor may induce a gradual depression of photosynthesis due to stomatal closure under both stress treatments. However, under NaCl treatment, a ionic factor (uptake and accumulation of excess Na+) may have direct effects on electron transport and cause more severe photosynthetic depression. The drought tolerance mechanism of BR 8 was insufficient to maintain single-leaf photosynthesis under salinity. and S. Muranaka, K. Shimizu, M. Kato.
In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO2 concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the Fv/Fm in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants. and I. Cechin ... [et al.].
Plant growth, chlorophyll (Chl) content, photosynthetic gas exchange, ribulose-1,5-bisphosphate carboxylase (RuBPCO) enzyme activity, and Chl fluorescence in radish (Raphanus sativus var. longipinnatus) plants were examined after turnip mosaic virus (TuMV) infection. Plant fresh mass, dry mass, Chl content, net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), and RuBPCO activity were significantly lower in infected plants after 5 weeks of virus infection as compared to healthy plants. The 5-week virus infection did not induce significant differences in intercellular CO2 concentration (Ci, photochemical efficiency of photosystem 2, PS2 (Fv/Fm), excitation capture efficiency of open PS2 reaction centres (Fv'/Fm'), effective quantum efficiency of photosystem 2 (ΔF/Fm'), and photochemical quenching (qP), but non-photochemical quenching (qN) and alternative electron sink (AES) were significantly enhanced. Thus the decreased plant biomass of TuMV-infected plants might be associated with the decreased photosynthetic activity mainly due to reduced RuBPCO activity. and Y.-P. Guo ... [et al.].