In this brief communication we provide an estimate of the part of the incident solar energy used for oxygen evolution as well as the time, in years, needed for the generation of the present amount of molecular oxygen in the biosphere by photosynthesis on land and in the ocean. We find this to be ~3,000 yr. We also find that the ocean produces 22% more oxygen than the land surface., A. Yu. Borisov, L. O. Björn., and Obsahuje bibliografické odkazy
The variable fluorescence at the maximum Fm of the fluorescence induction (Kautsky) curve is known to be substantially suppressed shortly after light adaption due to nonphotochemical qE quenching. The kinetic pattern of the dark decay at Fm consists of three components with rates ~20, ~1, and ~0.1 s-1, respectively. Light adaptation has no or little effect on these rate constants. It causes a decrease in the ratio between the amplitudes of the slow and fast one with negligible change in the small amplitude of the ultra-slow component. Results add to evidence for the hypothesis that the dark-reversible decrease in variable fluorescence accompanying light adaptation during the P-S phase of the fluorescence induction curve is due to an alteration in nonphotochemical qE quenching caused by changes in the trans-thylakoid proton motive force in response to changes in the proton conductance gH+ of the
CF0-channel of the CF0·CF1·ATPase., W. J. Vredenberg., and Obsahuje bibliografické odkazy
The review deals with objective reasons that limit the use of chlorophyll fluorescence induction kinetics (Chl FIK) method in plant ecology. Based on the ontogenetic approach (analysis and comparison of the dynamics of the Chl fluorescence ratio Fp/Fs and physiological characteristics of plant leaves in ontogeny) possible criteria for the estimation of general plant resistance of photosynthetic apparatus (PSA) to prolonged stress affects are proposed. One of these criteria is the presence or absence of a steady-state phase in the dynamics of Chl fluorescence ratio Fp/Fs (or Rfd) of plant leaves after they stop growing. We also propose to use the duration of the steady-state phase and variability of Chl fluorescence ratios Rfd and Fp/Fs in this period for quantitative assessment of plant PSA resistance to prolonged stress during plant leaf ontogeny. and T. V. Nesterenko, A. A. Tikhomirov, V. N. Shikhov.
Ontogenetic changes of rates of photon-saturated photosynthesis (Psat) and dark respiration (RD) of individual leaves were examined in relation to nitrogen content (Nc) in rice, winter wheat, maize, soybean, field bean, tomato, potato, and beet. Psat was positively correlated with Nc as follows: Psat = CfNc + Psat0, where Cf and Psat0 are coefficients. The value of Cf was high in maize, medium in rice and soybean, and low in field bean, potato, tomato, and beet, of which difference was not explained by ribulose-1,5-bisphoshate carboxylase/oxygenase (RuBPCO) content. RD was explained by Psat and/or Nc, however, two models must be applied according to plant species. RD related linearly with Psat and Nc in maize, field bean, and potato as follows: RD = a Psat + b, or RD = a'Nc + b', where a, a', b and b' are coefficients. In other species, the RD/Psat ratio increased exponentially with the decrease of Nc as follows: RD/Psat = a exp(b Nc), where a and b are coefficients. Therefore, RD in these crops was expressed as follows: In(RD) = ln(a Psat) + b Nc, indicating that RD in these crops was regulated by both Psat and Nc. and M. Osaki ... [et al.].
Characteristic features of stomatal apparatus, i.e, stomatal density, area of the stomatal poruš, relative stomatal area and diffusion resistance (r^) were examined in young (10 d) and old (30 d) leaves of four sugar beet cultivars (Allyx, Arigomono, Monohil and Primahill). Since the plant age was also considered to be an important ontogenetic factor, all measurements were repeated at plant ages of 40, 47, 57 and 65 d. Genotypical differences among the cultivars studied could be explained in terms of the level of ploidy, i,e. an increasing number of chromosome sets was accompanied by an increase of stomatal size and a decrease of stomatal density. The other stomatal characteristics did not significantly differ among the cultivars. The increase in plant age resulted in a higher stomatal density and a gradually decreasing stomatal size. These phenomena generally induced a plant ontogeny controlled increase of the relative stomatal area of all leaf series. Young leaves showed higher stomatal densities, but the stomata were smaller and póre area was reduced by 40 to 60 %, compared to the old leaves. The young leaves also exhibited a smaller r^.
The progressive decline in cotton leaf photosynthesis with season could be accounted for by gaining an insight into ontogenic changes in chloroplast integrity and epicuticular wax ultrastructure. Therefore, the sequence of ultrastructural changes in chloroplast and epicuticular wax morphology were probed in 10-, 20-, 40-, and 60-d-old cotton (Gossypium hirsutum L.) leaves using electron microscopy. Scanning electron microscopy illustrated that the epicuticular wax on the periclinal walls of the convex epidermal cells occurred as striations and persisted as such during the course of leaf aging. The degree of wax spread, however, increased as the leaf progressed towards senescence. Transmission electron microscopy revealed that a 20-d-old photosynthetically active leaf possessed healthy chloroplasts (6.8 μm long and an area of 9.7 μm2) with absolute membrane integrity depicted by large appressed grana stacks of thylakoids interconnected by non-appressed stroma lamellae. The thylakoid membrane network was oriented parallel to the long axis of the chloroplast and a few small plastoglobuli (1.85 μm2) scattered in the stroma. Conversely, membrane integrity was lost with leaf age after 20 d as evidenced by disruption of the grana and stroma lamellae. Concurrent with the membrane damage, extensive occlusion of chloroplast by several large spherical plastoglobuli (5.68 μm2) occurred, the rate of occlusion increased with leafage distending the chloroplast as evidenced by proliferation of its cross-sectional area (12.8 μm2). Of particular interest was the finding that the plastoglobuli ensued through the chloroplast envelope into the cytoplasm. The progressive loss of chloroplast membrane integrity coupled with increased leaf waxiness may have limited photosynthetic activities of cotton leaves during senescence. and B. R. Bondada, D. M. Oosterhuis.
Reaction centres (RC) from the purpie bacterium Rhodohacter sphaeroides (strain R-24.1 and carotenoid-free mutant R-26.1) were separated and immobilized in isotropic and stretched polyvinyl alcohol (PVA) films. Absorption, fluorescence, delayed luminescence (8-300 K) and photoacoustic spectra (PAS) of immobilized samples were measured. The RC from wild strain R-24.1 and ffom carotenoid-free mutant R-26.1 were differently oriented in the stretched polymer film. In R-24.1 the long axis of the RC complex was directed under some angle with respect to the perpendicular direction to the PVA film plane, whereas in R-26.1 it was almost perpendicular to this plane. The shapes of linear dichroism (LD) of both strains were different. Delayed luminescence (DL) bands were located in a similar wavelength range as the bacteriochlorophyll and bacteriopheophytin prompt fluorescence bands. Intensity of DL was independent of temperature in the 8-300 K range. The intensity of DL was about three time lower than that of the fluorescence. The dependence of PAS on the frequency of radiation modulation and on the phase shift between modulated acting radiation and measured PAS showed that part of the thermal deactivation was undergoing slowly. Intensity ratio of the slow component to the fast one and/or decay time of the slow component of thermal deactivation were different for various chromophores and for RC ffom the two strains of bacteria.
Principal Component Analysis, an ordination technique frequently ušed in phytosociological ecology, has been successfully applied in an attempt to consolidate unknown factors and processes responsible for influencing and modulating photosynthesis determining sugar beet leaf characteristics. Starting from a rough data matrix which consisted of the observed values of 18 cytological, anatomical and ecophysiological leaf parameters, measured in 32 leaf series, this technique calculated the co-ordinates of 32 entities with respect to a whole new set of principál axes. The ordination of all leaf entities was highly correlated with the relative increase of intemal (leaf) area, the total relative stomatal area and the chlorophyll a content. Since their arrangement on the main principál axis was also strongly determined by plant age, the conclusion could be drawn immediately that these three leaf parameters were significantly modulated by plant age. So, conclusions found in a rather subjective way were confirmed by this mathematical ordination technique.