Parameters of the fast chlorophyll (Chl) fluorescence induction (the O-J-I-P curve) of plants of winter wheat grown in the field canopy were statistically tested for Gaussian distribution. Five different statistical methods showed that the obtained values did not obey the Gaussian distribution law. The presentation of the parameters with the help of the mean and standard deviation masks the information about statistical properties of the values. Thus, we recommend to present the parameters by means of median, quartiles, and minimum and maximum values rather than by means of the mean and standard deviation. and D. Lazár, J. Nauš.
The photosynthetic CO2 exchange rate, chlorophyll fluorescence and P700 oxidation (absorption at 830 nm) were recorded in attached leaves of sunflower plants grown in soil by irradiance 460 pmol m'2 s‘i. Ehiring the photosynthesis in 510 cm^ m*3 CO2, 1 % O2, photosystem 1 (PS 1) effíciency was ahnost totally determined by the donor side oxidation under all irradiances. Fluorescence data showed that this control was exercised mostly by ApH-dependent plastoquinol oxidation. At 1.5 pM intracellular [CO2], the PS 1 reduction level on the acceptor side became signifícant and increased as [CO2] -> 0. ApH controlled the electron flow when the rate exceeded the value of 50 pmol(e‘) m'2 s‘i, which was close to the rate supporting photorespiration and CO2 reassimilation at CO2 compensation concentration in 21 % O2. The ApH ability to control the electron transport rate adequately prevented electron carriers reduction at PS 1 acceptor side, with stomata dosed under stress. When the low CO2 oř carbon reduction enzymes inactivation restricted the electron transport downstream of PS 1, open PS 1 centres (oxidised on acceptor sides) percentage declined in proportion to CO2 uptake rate. This makes us doubt the common belief that the rapid electron transport in photosynthesis involves interconnected, mobile electron carrier pools of plastocyanin and ferredoxin (Fd). Rather, the implications are explored in terms of supercomplexes involving cytochrome b(Jf, PC, PS 1, Fd and Fd-NADP reductase.
Quaternary ammonium salts, besides having an inhibitory effect which was studied by Králová eí al. (1992), exhibited at low concentrations a stimulating effect upon the oxygen evolution rate in spinách chloroplasts. The stimulation is caused by changes in arrangement of thylakoid membranes due to a detergent-like effect of the compoimds.
The stimulating effect of 1-alkyl-1-ethyl piperidinium bromides on the oxygen evolution rate in spinách chloroplasts was caused by rearrangement of thylakoid membrane.
In the evergreen Quercus rotundifolia and the co-existing deciduous Q. faginea we studied the diurnal variations in photosynthetic capacity (Pmax), measured as the rate of O2 evolution at photon and CO2 saturation, and in the rate of net CO2 assimilation (PN) in the field during the period of maximum photosynthetic activity. Our aim was to check the contribution of stomatal and non-stomatal limitations to the diurnal variation in photosynthesis, and to study the differences between both species. Q. faginea leaves displayed lower mass per unit area and higher nitrogen content than Q. rotundifolia leaves. The maximum stomatal conductance and PN in the field were higher in Q. faginea than in Q rotundifolia. Also Pmax of Q. faginea was higher than that of Q. rotundifolia. Both species attained in the field a high percentage of the Pmax (around 82 % for Q. faginea and 73 % for Q. rotundifolia). This indicates reduced stomatal limitation of photosynthesis under favourable conditions, especially in Q. faginea. PN underwent a sharp decrease towards mid-day in association with increase in the atmospheric vapour pressure deficit and decrease in the leaf water potential. Pmax was also reduced during mid-day. This demonstrated the contribution of mesophyll limitations to the PN in the two species under stress. The mesophyll limitation of photosynthesis seemed to be similar for both species, independently from the differences in leaf traits between them. and S. Mediavilla, H. Santiago, A. Escudero.
Two wheat {Triticum aestivum L.) cultivars, Trakia (drought-sensitive, DS) and Slavianka 196 (drought-tolerant, DT), were subjected to water stress induced by polyethyleneglycol (PEG) 6000; 15 % PEG for 6 h (mild stress); 25 % PEG for 6 h and 15 % PEG for 24 h (severe stress). Exposure of plants to water stress led to a noticeable decrease in both the initial slope of net photosynthetic rate to intercellular CO2 concentration {Pfilc^ curves and the maximum P-^. Ribulose 1,5-bisphosphate carboxylase (RuBPC) activity was almost unchanged under mild stress while under severe stress it was reduced by about 26-27 %. The ratio of variable to maximal chlorophyll fluorescence did not change which implied that there was little effect of examined stress conditions on the photosystem 2 electron transport. The relative magnitude of stomatal and nonstomatal factors in limitation of photosynthesis depended on stress severity.