The effect of the low temperature acclimation and photoinhibitory treatment on photosystem 2 (PS 2) of the cold-unhardened and -hardened spinách leaves were studied by thermoluminescence emission. Acclimation as well as photoinhibition at 4 °C rose inactive PS 2 reaction centres which did not produce thermoluminescence.
Field experiments were conducted to explore the relationship between canopy apparent photosynthesis (F’N,can) ^nd grain yield of maize {Zea mays L.) and to determine over two years the effects of plant population density (PPD) on /'N.can- Yedan No. 4 hybrid (vertical leaf type) were grown at fíve PPD in 1989 and 1990. Measurements of /"n can were made throughout the growth period in a large plastic covered chamber put over a segment of the canopy. Maximum values of /^N.can ca. 1500 pmol(photon) m'^ s'* were about 2.8 mg(C02) m‘2(soil area) s'* at the anthesis stage and they decreased with age throughout grain filling. Differences in /^N can between PPD could be attributed to leaf area index (LAI) or radiant energy interception. There was a quadratic regression between and LAI. The critical LAI for Pn can was about 4 to 6 for Shendan No. 7 and Yendan 4, respectively. Grain yield also differed between PPD, the range was 850 to 1140 g m'^ in the two cultivars. Increasing PPD of Yedan No. 4 up to about 9 plants per m^ and decreasing PPD of Shendan No. 7 to about 4 plants per m^ in a non-stressed environment should increase grain yield. Pfj can anthesis was positively correlated with biological {r = 0.8750** to 0.9797**) and grain (r = 0.8932** to 0.9914**) yields.
The effect of repeated infestations of BALB/c mice with Ixodes ricinus (L.) nymphs on tick borne encephalitis (TBE) virus infection was studied. Enhancement of nymphal feeding, occurring in noninfected mice during the quaternary infestations, was less apparent or absent in female nymphs engorged on TBE virus infected mice. The mice infected with TBE virus during quaternary tick infestation survived significantly longer (P < 0.01) than mice infected with TBE virus during the primary tick infestation. The mean titre of virus in murine blood (determined by plaque assay) was significantly lower (P < 0.01) and the number of nymphs acquiring virus was reduced (P < 0.05) when feeding on hosts infected during the quaternary infestation. The results indicate that repeated infestations of I. ricinus nymphs on BALB/c mice, although enhancing tick feeding, reduced infection with TBE virus when inoculated intraperitoneally.
Various physiological characteristics of Cj and C4 plants (14 species) grown along a salinity gradient were studied. The majority of plants occupying salt-marshes were succulent chenopods, mainly C4 annuals. The ash content of assimilating organs of plants was higher and osmotic potential lower in species grown under increasing soil salinity. The plants of the NADP-ME group accumulated more K than Na. Large amounts of Na"^ and CT characterized the NAD-ME plants and perennial C3 plants from sites with high soil salinity, Net photosynthetic rate (P^) and chlorophyll content were decreased in species grown under high salinity. Dark respiration was depressed by salinity to a lesser extent than P^.
Freezing of thylakoid membranes in the presence of 0.1 M NaCl and increasing concentrations of serine changed the photochemical actívity of photosystem (PS) 2 with beginning of freezing, while the PSI mediated electron transport was altered after a 24 h storage at -20 °C.
In greenhouse experiments the efFect of simulated acid rain (mist of H2SO4) treatment on i'*C02 fixation, ribulose-l,5-bisphosphate carboxylase (RuBPC), nitráte reductase (NR) and nitrite reductase (NiR) activities in Vigna sinensis L. and Phaseolus mungo L. was investigated at different pH. Seedlings exposed to acidic mists of pH 5.6, 4.0 and 2.0 for 5 d showed significant reduction in *“*€02 fixation, RuBPC, NiR and especially NR activities. Sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) of crude leaf extracts of RuBPC indicated a significant loss of 55 and 15 kDa polypeptides at pH 2.0 in both the crop plants. The reduction in the RuBPC activity in seedlings grown under acidic mists correlated well with the CO2 fixation. NR activity was affected more than the NiR activity.
Both the synthesis of apoprotein P700 with molecular mass of 72 kDa and asseinbly of chlorophyll (Chl) a-protein of photosystem (PS) 1 were blocked by lincoinycin (inhibitor of translation in chloroplasts). Synthesis of 48 and 43,5 kDa polypeptides belonging to the PS2 complex were also suppressed. Chl a forms of PS2 reaction centi e (RC) at 683 nin and of PS 1 RC at 690, 696 and 705 nm disappeared, Relative Chl h content and fluorescence bands ratio F736/F686 increased significantly Cycloheximide (inhibitor of translation in cytoplasin) ti eatinent resulted in reduction of polypeptides of the light-harvesting Chl a//i-protein complex (LFIC) in the 28.5- 25.5 kDa region. At the same time a relatively smaller decrease was observed of two Chl foirns of the LHC: Chl by 3.8 % and Chl by 10.2 % (12.4 and 34.3 % in the contiol, respectively). The fluorescence bands ratio F736/F686 decrease in low temperature spectra was possibly connected with the LIlC-1 and LIlC-2 synthesis blocking.
Seedlings of Erythrina variegata Lam. exposed to flooding for 10 d showed significant reduction in height, growth rates (leaf area in plant, leaf area index, relative growth rate, and specific leaf mass), biomass, chlorophyli (Chl) and carotenoid contents, and thylakoid membrane organization. Application of triacontanol partially compensated these effects and promoted height, biomass and Chl content. Starch and sugar contents were significantly higher in leaves of flooded seedlings.
The effect of spraying triacontanol (Tria) solution (1 g m'^) on •'*C02 fíxation, ribulose-l,5-bisphosphate carboxylase (RuBPC), nitráte reductase (NR) and photosystem (PS) activities in waterlogged Erythrina variegata Lam. was investigated under field conditions. Seedlings exposed to flooding for 10 d showed a significant reduction in •‘♦CO2 fíxation, and in NR, RuBPC and PS2 activities. Electrophoretic analysis of thylakoid polypeptides indicated a significant loss of 47, 43, 33, 25, 23, 17 and 15 kDa polypeptides in flooded seedlings. However, the application of Tria partially ameliorated the effect of flooding and promoted the above activities. The site of flooding injury was at the oxidation site of PS2 prior to the hydroxylamine donating site and perhaps close or after the diphenylcarbazide donating site. The increase in the RuBPC activity in Tria-treated seedlings under flooding correlated well with the changes in CO2 fíxation rate.
Cauliflower (Brassica oleracea L. var. botrytis) plants subjected to Zn defíciency showed decreased leaf water potential and transpiration rate, and increased leaf thickness, and accumulation of sugars and starch. Zn-deficient leaves also showed decreased photosynthetic rates (P^) and compensation irradiance and increased apparent quantum efficiency. Decrease in leaf chlorophyll (Chl) content due to Zn defíciency, though signifícant on fresh mass unit was insignifícant on leaf area unit. Decreased was not attributable to the effects of Zn defíciency on Chl content upto 51 d of treatment. Zn-defícient leaves showed an insignifícant decrease in photosynthetic O2 evolution at saturating irradiance and CO2 supply; signifícant decreases in P^, stomatal conductance and intercellular CO2 concentration when the leaves were supplied with CO2 at atmospheric concentration suggest that stomatal limitation contributes signifícantly towards decreased P^ in Zn-defícient leaves.