The age dependence of the photosynthetic performance, chlorophyll fluorescence and chloroplast ultrastructure of green form and Chl ft-deficient form (aurea) of tobacco Su/su mutant were compared. The most pronounced differences between the aurea and green tobacco found in young leaves diminished with leaf age. Slower accumulation of the photosynthetic pigments during the development of aurea leaves was accompanied by a slower accumulation of LHC antennae of both photosystems, particularly that of PS2, and by retention of an increase in the capacity of PS2 photochemistry, measured as Fy/FM The ratio Fv/Fm, however, increased rapidly during maturation of aurea leaves, and fmally the mature aurea leaves exhibited higher values of this ratio than the green ones. Rates of photosynthesis at saturating irradiance (Epiax) saturating CO2 concentration (/’sat) decreased with leaf age for both aurea and green tobacco, being always higher in aurea leaves than in leaves of green tobacco of comparable age. AU these characteristics indicated retarded development of aurea leaves. Also the chloroplast ultrastructure, particularly grana formation, exhibited slower development. The decrease in /Wx and with leaf age in both tobacco forms and retardation in the development of aurea leaves can explain higher value of usually found in aurea tobacco.
We examined the carbon budget of young winter wheat plants and their associated microorganisms as affected by a doubling of the atmospheric CO2 concentration (700 µmol mol-1). Plants were grown hydroponically in pre-sterilised sand at a controlled irradiance and temperature regime. Net photosynthesis (PN) and respiration (RD) rates of roots and shoots were measured continuously, plant growth and carbon distribution in the plant-root medium-associated microorganism system were determined destructively in interval-based analyses. PN in elevated CO2 grown plants (EC) was 123% of that in the control (AC) plants when averaged over the whole life span (39-d-old plants, 34 d in EC), but the percentage varied with the developmental stage being 115, 88, and 167% in the pretillering, tillering, and posttillering phase, respectively. There was a transient depression of PN, higher amplitude of day/night fluctuations of the chloroplast starch content, and depression of carbon content in rhizosphere of EC plants during the period of tillering. After 34 d in EC, carbon content in shoots, roots, and in rhizodepositions was enhanced by the factors 1.05, 1.28, and 1.96, respectively. Carbon partitioning between above and belowground biomass was not affected by EC, however, proportionally more C in the belowground partitioning was allocated into the root biomass. Carbon flow from roots to rhizodepositions and rhizosphere microflora was proportional to PN; its fraction in daily assimilated carbon decreased from young (17%) to order (3-4%) plants. and H. Šantrůčková ... [et al.].
The photochemical activity of native Central Siberian Scots pine trees (Pinus sylvestris L) was estimated from the middle of February to the middle of March 2001. We measured chlorophyll (Chl) fluorescence in attached intact needles from trees located approx. 30 km west of the Yenisey river (60°44'N, 89°09'E) near the village of Zotino. In this period, the air temperature varied between -39 °C and +7 °C. At temperatures below -10 °C, P. sylvestris needles did not exhibit any variable Chl fluorescence during the daylight period. During the night, however, the effective quantum yield of photosystem 2 (PS2) photochemistry, Φ2 [Φ2 = (Fm' - Ft)/Fm'), increased from values near zero to values between 0.05 and 0.20 depending on the needle temperature and sample investigated. The increase started soon after dusk and lasted for 3-6 h depending on the temperature. A faster increase of Φ2 was found for temperatures around -16 °C, and lower rates occurred at lower temperatures. Irrespective of the temperature, Φ2 decreased rapidly to near zero values at dawn, when the photosynthetic photon flux density increased to about 1-5 µmol m-2 s-1, and remained near zero throughout the day. At temperatures higher than -10 °C, the diurnal decrease and the nocturnal increase of Φ2 were less distinct or disappeared completely. Hence the winter-adapted Scots pine maintains some photochemical activity of PS2 even at extremely cold temperatures. The capacity of photochemical reactions below -10 °C is, however, very limited and PS2 photochemistry is saturated by an extremely low irradiance (less than 5 µmol m-2 s-1). and P. Šiffel, J. Šantrůček.
Life and research results of Pavel Siffel, a talented but untimely deceased Czech scientist in photosynthesis, are reviewed. He studied biophysics and physiology of chlorophyll, its complexes with proteins, their absorption and fluorescence spectra, activities in mutants and transformants, dealt with chlorophyll biosynthesis and protochlorophyllide photoreduction, pigments in plants grown at CO2 deficiency and under simulated acid rain, with changes accompanying leaf and plant development, photobleaching, etc. He participated in construction of specialised spectrofluorometers, finally he built the kinetic spectrophotometer SpeKin. and J. Květoň ... [et al.].
Environmental factors that induce spatial heterogeneity of stomatal conductance, gs, called stomatal patchiness, also reduce the photochemical capacity of CO2 fixation, yet current methods cannot distinguish between the relative effect of stomatal patchiness and biochemical limitations on photosynthetic capacity. We evaluate effects of stomatal patchiness and the biochemical capacity of CO2 fixation on the sensitivity of net photosynthetic rate (PN) to stomatal conductance (gs), θ (θ = δP N/gs). A qualitative model shows that stomatal patchiness increases the sensitivity θ while reduced biochemical capacity of CO2 fixation lowers θ. We used this feature to distinguish between stomatal patchiness and mesophyll impairments in the photochemistry of CO2 fixation. We compared gas exchange of sunflower (Helianthus annuus L.) plants grown in a growth chamber and fed abscisic acid, ABA (10-5 M), for 10 d with control plants (-ABA). PN and gs oscillated more frequently in ABA-treated than in control plants when the leaves were placed into the leaf chamber and exposed to a dry atmosphere. When compared with the initial CO2 response measured at the beginning of the treatment (day zero), both ABA and control leaves showed reduced PN at particular sub-stomatal CO2 concentration (ci) during the oscillations. A lower reduction of P N at particular g s indicated overestimation of ci due to stomatal patchiness and/or omitted cuticular conductance, gc. The initial period of damp oscillation was characterised by inhibition of chloroplast processes while stomatal patchiness prevailed at the steady state of gas exchange. The sensitivity θ remained at the original pre-treatment values at high gs in both ABA and control plants. At low gs, θ decreased in ABA-treated plants indicating an ABA-induced impairment of chloroplast processes. In control plants, gc neglected in the calculation of gs was the likely reason for apparent depression of photosynthesis at low gs. and J. Šantrůček ... [et al.].
Differences between photosynthetic characteristics of chlorophyll (Chl) 6-deficient aurea mutant (Su/su) and the green (su/su) variety of Nicotiana tabacum were tested. Fully mature leaves of 3-5-month-old plants grown in potted soil were investigated. Main differences were found as follows: Respective Chl a and b contents were 3 and 5 times lower in aurea plants, while xanthophylls and carotenes contents per unit of Chl were higher. The content of light-harvesting complex (LHC) was lower and LHC composition differed in aurea mutant. PS 1 activity calculated per unit of Chl content was higher in aurea mutant. The green variety showed the lower photosynthetic rates (Pn) at saturating irradiances whether calculated on the Chl or leaf area basis. At excessive light declined with green plants. Carboxylation efficiency (CE) (CO2 response slope of Pjj at low CO2 concentrations) was higher for aurea mutant. Time- integrated intercellular CO2 concentrations derived from ^^C discrimination were higher for aurea mutant (304 cm^ m'^) than for green plants (283 cm^ m'^), which together with higher mean stomatal conductance in aurea matched CE differences.