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.
Chlorophyll (Chl) content, photochemical activity of chloroplasts as well as photosynthetic and crop productivity were studied in different winter hexaploid Triticale (xTriticosecale Witt.) lines and their F1 hybrids. Heterosis enhanced Chl content, photosynthetic potential, photosynthetic productivity, and grain yield only in several F1 hybrids of Triticale. Indication in some genotypes of close correlations among morphological structure, Chl content, photochemical activity of chloroplasts, photosynthetic potential, and plant productivity may be used in breeding practice of Triticale. and S. N. Kabanova ... [et al.].
CO2 and O2 exchange rates, chlorophyll fluorescence and P700 oxidation (absorption at 830 nm) were recorded in Helianthus amuus L. leaves grown in soil in a growth cabinet. Phase-portraits of CO2 exchange rate plotted against three other parameters were ušed to interpret control of electron transport during photosynthesis oscillations, initiated by transfer from air to the saturating CO2. Plots of the CO2 exchange rate vs. P700 revealed that the P700 part which remained oxidized was almost proportional to CO2 exchange rate during both the ascending and descending phase of oscillations.
Inactivation of photosynthesis during atmospheric and osmotic (highly concentrated NaCl or sucrose solutions) dehydration was monitored by measurement of chlorophyll fluorescence induction (OIP-phase, Kautsky-curves) in three lichen species. The induction curves were changed in a very similar way by all three treatments. All dehydration effects were rapidly reversible after rehydration. At relatively mild water stress, the rise time to the transient peak Fp was prolonged, and the variable part of fluorescence was diminished. In addition, at severe water stress, a considerable decline of the F0 value was observed. For NaCl treatment this effect started at water potentials <-8.5 MPa in P. aphthosa, <-12 MPa in H. physodes, and <-21 MPa in L. pulmonaria. Above these water potentials, our observations are in agreement with values from desiccation-tolerant algae, higher plants, and lichens, where an inactivation on the photosystem 2 (PS2) donor side has been postulated. At very low water potentials, the decrease in F0 probably monitors changes in the organization of the antenna apparatus of PS2. and M. Jensen, Samira Chakir, G. B. Feige.