We investigated seasonal patterns of photosynthetic responses to CO2 concentrations in Spartina alterniflora Loisel, an aerenchymous halophyte grass, from a salt marsh of the Bay of Fundy (NB, Canada), and from plants grown from rhizome in controlled-environment chambers. From late May to August, CO2 compensation concentrations (Γ) of field-grown leaves varied between 2.5-10.7 cm3(CO2) m-3, with a mean of 5.4 cm3(CO2) m-3. From September onwards field leaves showed CO2 compensation concentrations from 6.6-21.1 cm3(CO2) m-3, with a mean of 13.1 cm3 m-3 well into the C3-C4 intermediate range. The seasonal variability in Γ did not result from changing respiration, but rather from a sigmoidal response of net photosynthetic rate (PN) to applied CO2 concentration, found in all tested leaves but which became more pronounced late in the season. One explanation for the sigmoidal response of PN to external CO2 concentration could be internal delivery of CO2 from roots and rhizomes to bundle sheath cells via the aerenchyma, but the sigmoidal responses in S. alterniflora persisted out to the tips of leaves, while the aerenchyma extend only to mid-leaf. The sigmoidicity persisted when CO2 response curves were measured from low to high CO2, or from high to low CO2, and even when prolonged acclimation times were used at each CO2 concentration. and M. O. Bärlocher ... [et al.].
We studied the developmental changes in photosynthetic and respiration rates and thermal dissipation processes connected with chloroplasts and mitochondria activity in etiolated wheat (Triticum aestivum L., var. Irgina) seedlings during the greening process. Etioplasts gradually developed into mature chloroplasts under continuous light [190 μmol(photon) m-2 s-1] for 48 h in 5-day-dark-grown seedlings. The net photosynthetic rate of irradiated leaves became positive after 6 h of illumination and increased further. The first two hours of de-etiolation were characterized by low values of maximum (Fv/Fm) and actual photochemical efficiency of photosystem II (PSII) and by a coefficient of photochemical quenching in leaves. Fv/Fm reached 0.8 by the end of 24 h-light period. During greening, energy-dependent component of nonphotochemical quenching of chlorophyll fluorescence, violaxanthin cycle (VXC) operation, and lipoperoxidation activity changed in a similar way. Values of these parameters were the highest at the later phase of de-etiolation (4-12 h of illumination). The respiration rate increased significantly after 2 h of greening and it was the highest after 4-6 h of illumination. It was caused by an increase in alternative respiration (AP) capacity. The strong, positive linear correlation was revealed between AP capacity and heat production in greening tissues. These results indicated that VXC in chloroplasts and AP in mitochondria were intensified as energy-dissipating systems at the later stage of greening (after 4 h), when most of prolamellar bodies converted into thylakoids, and they showed the greatest activity until the photosynthetic machinery was almost completely developed. and E. V. Garmash ... [et al.].
Developmental changes of plant in the regulation of photosynthate distribution of leaves were studied in hydroponically cultivated rice by the 14CO2 tracer technique and analysis of the activity of the regulatory enzymes, sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK). The distribution of primary photosynthates into sugars, amino acids, organic acids, sugar phosphates, proteins, and polysaccharides was determined by column chromatography. The relative primary photosynthate distribution to the sugar phosphate fraction was significantly larger in the 5th leaf than in the 6th one. Correspondingly, the Vmax of PEPC was significantly higher in the 5th than in the 6th leaf, while no significant differences between leaves were detected in the other enzymes. As a consequence, the ratio of the Vmax of SPS and PEPC was lower in the 5th than in the 6th leaf. As the 5th leaf develops before panicle initiation in rice, it predominantly supports vegetative growth, while the 6th leaf develops after panicle initiation and thus contributes mainly to reproductive growth. We conclude that the physiological properties of each leaf are regulated developmentally. When the 6th leaf became fully expanded (corresponding to the panicle initiation stage of plant), the distribution pattern of 14C was transiently changed in the 5th leaf, indicating that individual organs that are mainly involved in vegetative development are affected to some extent by the whole-plant-level physiological transformation that occurs at the transition from the vegetative to the reproductive stage. and T. Shinano ... [et al.].
Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280-320 nm; 60 µmol m-2 s-1) exposure alone and in combination with photosynthetically active radiation (PAR; 400-800 nm; 200 µmol m-2 s-1) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O2 evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples. and M. K. Pradhan ... [et al.].
mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N0.5, N3.0). The relative gene expression patterns were similar in all leaves except for 9th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS Vmax, SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS Vmax was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5th and 7th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9th and flag leaves). PEPC activity and SPS Vmax decreased with declining leaf N content. After using 14CO2 the 14C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more 14C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more 14C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the N- or C-pool, respectively, regardless of the leaf N status. and T. Shinano ... [et al.].
The paper contains short description of a special device developed for study of electrical after-effect in vegetable cellular tissues after short electric pulses applied to the tissue. The device contains generator of the pulses and the microprocessor controlling circuits for time arrangement of the pulse amplification and collection of data for further evaluation. The pulses are based on AC signal with frequency 10-100 kHz with the amplified voltage up to ±240V and duration 1-10 ms. After finishing the individual pulse, the AC source signal continues, but amplitude on the tissue is 21. 5times lower. The data about AC voltage and current intensity are continuously collected with frequency 800 kHz and then fed to PC USB input that was used to calculate time chart of electric properties of the tissue, its complex permittivity and specific complex conductivity. An example of the obtained results on potato tissue is given. and Práce obsahuje krátký popis speciálního zařízení vyvinutého pro studium elektrických jevů v zeleninové buněčné tkáni po krátkých elektrických pulsech. Zařízení se skládá z generátoru nosného signálu, mikroprocesorem řízené jednotky pro amplitudovou modulaci uvedeného nosného signálu, zesilovače pro výkonové zesílení a jednotky pro sběr dat pro další vyhodnocení. Užívá se nosný signál frekvence 10-100 kHz, modulovaný do pulsů strváním 1-10 ms a amplitudě do ±240 V. Po skončení individuálního pulsu střídavý signál pokračuje, ale jeho amplituda se snižuje 21,5krát; měření na tkáni pokračuje jako nedestruktivní. Data okamžitých hodnot napětí a proudu na zkoumané tkáni jsou snímána sfrekvencí 800 kHz. Tato data jsou přivedena na USB vstup PC a zde použita k výpočtu časového průběhu elektrických vlastností tkáně, její komplexní permitivity a měrné komplexní vodivosti. Analýza je demonstrována na příkladu (pletivo bramboru).