Effíciency of the energy transformation for CO2 fixation (E), and kinetics of the initial 02-mediated electron transport of Spimlina platemis (Gom.) Geitl. and Chlorella vulgaris Beijerinck cells were measured after adaptation to various growth irradiances (7) by means of the delayed fluorescence (DF) induction curves. Maxima of the membrane potential expenses during induction period were observed at I half saturating oxygen evolution; they were shifted according to growth 1 remaining higher in Spirulina than in Chlorella. The alterations of absorbance and fluorescence spectra at 25 oC after adaptation to / demonstrated changes in composition of pigments of algae, created to compensate for the imbalance in radiation absorption between the two photosystems. For Spirulina cells, the value of E was higher after growing under low /, or under blue radiation absorbed mainly by photosystem (PS) 1 (400-500 nm) with excitation by yellow (570 nm) radiation. For Chlorella cells, it was also higher after growing under low I. Under such conditions the half-rise time for DP-phase of DF induction curve decreased, which reflected an acceleration of kinetics of the initial electron transport between photosystems. An opposite situation was observed with Spirulina cells grown under high I or yellow radiation, and Chlorella cells from high I. Enhancement of effective PS2/PS1 ratio associated with decrease of reaction centre (RC) 2/RCl stoichiometry may be a cause of the increase of E and high membrane energization under saturating I in algae adapted to low 1.
Plants of pepper (Capsicum amuum L.) were grown in controlled environment chambers at ambient (360 pmol mol"*) and fluctuating pulse-enriched CO2 concentrations (700 pmol mol"* daily average, ranging from 500 to 3500 pmol mol"* = ECO2) under two water regimes. A decrease in plant growth and yield together with frequent visual injuries was found in plants growing under ECO2. Root/shoot ratio was greater, chlorophyll concentration and respiration rates were lower, and stomatal conductance and relative importance of alternativě pathway respiration were higher under ECO2. The negative effects of ECO2 were more intense under high water availability. The symptoms produced by ECO2 were similar to those of resource limitation, and were alleviated with increased nutrient supply. Constant elevated CO2 concentrations (700 pmol mol"*) increased pepper production and did not produce any of the injuries described for this erratic ECO2 treatment. Thus, it is probably the erratic nátuře of the CO2 concentration and not the gas itself that was causing the injiuy.
The reduction in chlorophyll (Chl) and protein contents and the increase in amino acid content in leaf discs in response to aqueous SO2 exposure under continuous irradiance were more expressed in Amaranthus paniculatus (C4 plant) than in Cajanus cajan (C3 plant). The content of SH-compounds increased more in pigeonpea than in amaranth leaf discs in response to SO2. Aqueous SO2 exposure also reduced the CO2 fixation and ribulose-l,5-bisphosphate carboxylase (RuBPC) and phosphoenolpyruvate carboxylase (PEPC) activities in leaf discs of both plant species. The differences in sensitivity of these plants to SO2 were related to their conversion efficiency of SO2 to less toxic substances and sulphydryl compounds.
Membrane-bound bicarbonate is believed by some to act as an essential activator of photosystem 2 (PS2) electron transport. Formáte and other inhibitory monovalent anions act by removing bound-bicarbonate. This belief relies to a great extent on the observation that formáte (100 mM) pretreated thylakoids exhibit a non- proportionality between Hill activity (HAR) and chlorophyll (Chl) concentration when preirradiated with bright radiation in reaction mixture that contains only 5 mM formáte. The non-linearity was attributed to a supposed loosening of residual bicarbonate still present after formáte treatment and which would be more abundant at higher Chl concentrations. In repeating this experiment, we observed an increase in HAR at higher Chl concentrations in preirradiated, but also in non-preirradiated samples, the latter were simply left in the dark for 3 min before measurements were made. Therefore, preirradiation is not needed to restore some HAR in formáte pretreated samples; a 3 min wait in the electrode chamber at low formáte concentration is sufficient to partially relieve the formáte inhibition of PS2 activity. Moreover, HAR in samples preirradiated by weak radiation, or not preirradiated at all, was directly proportional to Chl concentration. We can attribute the increase in activity to a dissociation of bound formáte, not necessarily to the effect of residual bicarbonate. Non-linearity in HAR with Chl concentration was found only in high- irradiance pretreated samples. We can attribute this to a greater amount of photoinhibition occurring in the dilute samples, where the effective irradiance was greater. There is no need to postuláte the existence of residual bound bicarbonate to explain these results.
Various physiological characteristics of Cj and C4 plants (14 species) grown along a salinity gradient were studied. The majority of plants occupying salt-marshes were succulent chenopods, mainly C4 annuals. The ash content of assimilating organs of plants was higher and osmotic potential lower in species grown under increasing soil salinity. The plants of the NADP-ME group accumulated more K than Na. Large amounts of Na"^ and CT characterized the NAD-ME plants and perennial C3 plants from sites with high soil salinity, Net photosynthetic rate (P^) and chlorophyll content were decreased in species grown under high salinity. Dark respiration was depressed by salinity to a lesser extent than P^.
Seedlings of Erythrina variegata Lam. exposed to flooding for 10 d showed significant reduction in height, growth rates (leaf area in plant, leaf area index, relative growth rate, and specific leaf mass), biomass, chlorophyli (Chl) and carotenoid contents, and thylakoid membrane organization. Application of triacontanol partially compensated these effects and promoted height, biomass and Chl content. Starch and sugar contents were significantly higher in leaves of flooded seedlings.
Effect of three Zn2+ concentrations, i.e. 0.075 (cl), 7.50 (c2) and 37.5 (c3) jiM, on rice seedlings was studied at three stages, i.e. 1, 14 and 21 d after transplantation. Typical deficiency symptoms were observed in both solution and sand cultures of cl and c2, but the effects were more pronounced in the solution culture. The c3 concentration was toxic. There was marked reduction in growth, chlorophyll (Chl) contents (particularly Chl b), Hill reaction activity, photophosphorylation rate (particularly non-cyclic photophosphorylation), thylakoid phosphorylation, and i'‘C02-fixation at the cl concentration. However, a similar reduction was also observed in thylakoid phosphorylation at the c3 concentration. Hence the optimum zinc concentration in the nutrient medium lied between c2 and c3 Zn2+. By regression the theoretical optimum Zn concentration was calculated as 19.20 pM (1.28 mg kg'i) Zn2+. Partitioning of ^'^C-photosynthates indicated reduced allocation to sugar and starch fractions and increased fřee amino acids concentration at the cl concentration and vice-versa at c2 and c3.
The influence of a cytokinin, 6-benzylaminopurine (BAP), on chloroplast structure was studied using biochemical methods and electron microscopy. The average degree of thylakoid stacking was determined by digitonin fractionation and differential centrifugation of chloroplasts from tobacco plantlets after treatment with different concentrations of BAP in agar medium during cultivation in viíro. An elevated concentration of BAP in the medium induced an increase in grana stacking. This was in accordance with the lowering of the chlorophyll a/b ratio in these chloroplasts. The relative amoímt of proteins and carotenoids increased in both stromal and (to a lesser extent) granal chloroplast thylakoid fractions with the BAP concentration. The electron microscopic studies revealed nearly the same volume density of thylakoid membranes within chloroplasts of BAP treated plantlets and control ones. In the BAP treated plantlets the chloroplasts were smaller and had a profound accumulation of starch inclusions and a more flattened shape than the chloroplasts of control plantlets. The volume density of plastoglobuli in chloroplasts did not decrease under the influence of BAP,
Changes in chlorophyll (Chl) a+b and a/b, senescence patterns during Chl loss and changes in net photosynthetic rate (P^) of four leaf flushes in Quercus acutissima and Q. serrata were studied. Emergent current-year leaves were classified according to the order of shoot growth flushes (first to fourth flush groups). Senescence patterns showed that leaf fall started from the leaf cohorts of the first flush group (the "oldest" leaf cohorts) which cuhninated upwards to the fourth leaf flush group (the "yoímgest" leaf cohorts). Senescence during Chl loss was accompanied by a decline in Pf^. A strong influence by the leaf flushing phenomenon on senescence was found which limited leaf bearing period and duration of Having large total leaf area and moderately long duration, tiie third and second leaf flush groups reflected the highest photosynthetic potential. This may be a positive attribute since the duration by which these plants maximize the use of its assimilatory organs is an important factor for their carbon fixation.
Photosynthetic assimilatíon of CO2 in a four-year-old plant of lilac, measured in April and in July, was compared. The results were calculated with regard to the surface area of the particular year groups of the stems and to the total surface area of the stems as well as to the globál surface area of the leaves of the plant. In April the stems were the only site of photosynthesis. In July the main organs of CO2 assimilatíon were the leaves, while the participation of the shoots in that period amounted to 2 %. In the process of photosynthesis in the stems mainly the endogenous CO2 was utilized, while the share of exogenous CO2 was 0.02 %. The potential photosynthesis was determined also on the basis of measurements of oxygen release by chloroplasts isolated from the bark and leaves. In July the production of oxygen by chloroplasts ffom the bark of all stems was 5 % of the amount of oxygen released by the chloroplasts isolated from the leaves. In April the production of oxygen by chloroplasts isolated from the bark of the particular year groups of the stems was higher than in July. In the process of CO2 assimilatíon by the bark and leaves the potential Chemical activity of chloroplasts was not fully utilized. The potential CO2 assimilatíon by chloroplasts isolated from the bark was 8.5 times greater than the measured results of CO2 exchange in July and 35.8 times greater in April.
In the dimorphic stag’s hom fem, Platycerium coronarium (Koenig ex Mueller) Desv., photosynthetic characters and chlorophyll (Chl) contents were deteiinined in both nést and pendulous fronds at different stages of ontogeny and at different positions along the longest length of each frond. Area-specific radiant energy- saturated net photosynthetic (P^) and dark respiration rates, dry mass-specific Chl content and quantum yield increased during frond development and decreased when senescence set in. Radiant energy-saturated and dry-mass specific Chl content were greatest in the youngest tissues of each frond. In addition to the functions ascribed to the nést (water and nutrient collection) and pendulous (reproduction) fronds, the results indicate the important roles of both frond types in providing Chemical energy to the growth and survival of the plant.
Sodium chloride salinity had enhanced the photosynthetic rate, photosystem 2 activity and chlorophyll synthesis in isolated leaf cells of Ipomoea pescaprae up to 200 mM NaCl. The salt treated plants did not show any shift in the mode of photosynthesis.
Morphological and ultrastructural changes, the chlorophyll (Chl) content and Chl a fluorescence induction were studied in primary leaves of runner beán plants (Phaseolus coccineus L. cv. Pi?kny Jaš) grown in Knop solution and treated with excess Cu [20 g(CuS04 x 5 H2O) m"^] at difíerent growth stages. The plants were exposed to the metal for 12 d. Cu added to the nutrient solution at the beginning growth stage induced significant leaf area reduction (31 %) as well as increase of Chl accumulation (148 %) and leaf density (122 %). No ultrastructural changes of chloroplasts were seen. Application of Cu at the advanced growth stage caused relatively smáli changes except local disturbances in stroma lamellae and leaf reduction to 70 % of control. Significant disorganization of chloroplast ultrastructure, smáli leaf area reduction (80 %) but specific leaf area increase (163 %) and leaf density decrease (67 %) were seen only in the primary leaves of plants treated with Cu at the finál stage of growth. These changes, similar to senescence response, were accompanied by Fy/Fo ratio decrease to 67 % in comparison with control.
During the growth cycle of micropropagated Juglans regia plantlets, phosphoenolpyruvate carboxylase (PEPC) activity was aiways higher than initial ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity. The ratio of PEPC/RuBPCO activities was higher during the first part of the exponential phase of growth and lower during the second part. The variations of PEPC activity were parallel to the soluble protein content and the variations of initial and total RuBPCO activities were parallel to the chlorophyll accumulation.
The ribulose 1,5-bisphosphate carboxylase (RuBPC) activity, protein content and net photosynthetic rate (P^) were estimated at monthly intervals from September 1990 to August 1991 in Chukrasia íabularis, Dolichandrom atrovirens, Eugenia jambolana, Gmelina arborea, Lamea coromandelica, Terminalia arjuna and Terminalia bellehca. The leaves of all these tree species showed significantly higher RuBPC activity during summer than in winter, when it was expressed on the basis of chlorophyll (Chl) content. RuBPC exhibited seasonal variations in its activity and these differed from one tree species to the other. When expressed on the basis of leaf area, the activity of RuBPC correlated with protein content, but not with P^.
The steady-state photosynthetic irradiance and temperature responses of Viola hondoensis and V. keiskei (Violaceae) growing in proximity in their nati ve environment and under three levels of artificial shade of relative irradiance (RI) of 7, 20 and 50 % were investigated. The maximum photosynthetic rates and temperature optima under natural conditions were much higher in V. keiskei than in V. hondoensis, except when in leaves of V. keiskei chlorophyll was degraded due to autumn frosts. When grown under artificial shade, both species had higher temperature optima as RI decreased. Since leaves under the three RI conditions experienced a similar leaf temperature, it was concluded that the shifts in the temperature responses with RI resulted from acclimation to the varying irradiance. The higher temperature optima observed in V. keiskei under natural conditions were probably due to the fact that V. keiskei grew in more shady microhabitats than V. hondoensis.