Annual plants transport a large portion of carbohydrates and nitrogenous compounds from leaves to seeds during the phase of reproductive growth. This study aimed to clarify how reproductive growth affects photosynthetic traits in leaves and matter transport within the plant in the annual herb Chenopodium album L. Plants were grown in pots and either reproductive tissues or axillary leaves were removed at anthesis. Matter transport was evaluated as temporal changes in dry mass (as a substitute of carbohydrates) and nitrogen content of aboveground organs: leaves, axillary leaves, stems and reproductive tissues. Photosynthetic capacity (light-saturated photosynthetic rate under ambient CO2 concentration), nitrogen, chlorophyll and soluble protein content were followed in the 20th leaf that was mature at the start of the experiment. Removal of reproductive tissues resulted in accumulation of dry mass in leaves and axillary leaves, and accumulation of nitrogen in stem as nitrogen resorption from leaves and axillary leaves proceeded with time. Removal of axillary leaves proportionally reduced dry mass and nitrogen allocation to reproductive tissues, thus affecting the quantity but not quality of seeds. Removal treatments did not alter the time course of photosynthetic capacity, nitrogen, chlorophyll or soluble protein content during senescence in the 20th leaf, but changed the photosynthetic capacity per unit of leaf nitrogen according to demand from reproductive tissues. Together, the results indicate that reproductive tissues affected carbon and nitrogen economy separately. The amount of carbon was adjusted in leaves through photosynthetic capacity and carbohydrate export from them, and the amount of nitrogen was adjusted by transport from stem to reproductive tissues. The plant's ability to independently regulate carbon and nitrogen economy should be important in natural habitats where the plant carbon-nitrogen balance can easily be disturbed by external factors.
The peptide surfactants are amphiphilic peptides which have a hydrophobic tail and a hydrophilic head, and have been reported to stabilize and protect some membrane proteins more effectively than conventional surfactants. The effects of a class of peptide surfactants on the structure and thermal stability of the photosynthetic membrane protein lightharvesting complex II (LHCII) in aqueous media have been investigated. After treatment with the cationic peptide surfactants A6K, V6K2, I5K2 and I5R2, the absorption at 436 nm and 470 nm decreased and the absorption at 500-510 nm and 684-690 nm increased. Moreover, the circular dichroism (CD) signal intensity in the Soret region also decreased significantly, indicating the conformation of some chlorophyll (Chl) a, Chl b, and the xanthophyll molecules distorted upon cationic peptide surfactants treatment. The anionic peptide surfactants A6D and V6D2 had no obvious effect on the absorption and CD spectra. Except for A6D, these peptides all decreased the thermal stability of LHCII, indicating that these peptides may reconstitute protein into a less stable conformation. In addition, the cationic peptide surfactants resulted in LHCII aggregation, as shown by sucrose gradient ultracentrifugation and fluorescence spectra. and S. Liu, Y. Qiu, D.-Y. Yu
The study investigated the effects of different CaCl2 concentrations (2, 5, and 10 mM) on photosynthetic enzymatic activities, photosynthesis, and chlorophyll fluorescence of tung tree seedlings under drought conditions. Plants were sprayed with either CaCl2 or distilled water until run-off. Irrigation was then withheld to induce drought stress. The strength of drought stress was evaluated by relative leaf water content and soil water content, which was 27.3 and 9.5% on day 0 and day 12, respectively. Drought stress decreased activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, chlorophyll (a+b) content, net photosynthetic rate, stomatal conductance, transpiration rate, electron transport rate, the maximal quantum yield of PSII photochemistry, and effective quantum yield of PSII in tung tree seedlings. The CaCl2 pretreatments alleviated the negative effect of drought stress to some degree on all the parameters mentioned above., Z. Li, X. F. Tan, K. Lu, Z. M. Liu, L. L. Wu., and Obsahuje bibliografii
Chemical modification of purifíed phosphoenolpyravate carboxylase (PEPC) from the crassulacean acid metabolism plant Crassula argentea Thunb. with the histidyl reagent diethylpyrocarbonate (DEPC) resulted in a transient increase in activity followed by a decrease of activity with time. This biphasic response was observed when the modifíed enzyme was assayed at both low (sub-K,^ and saturating substráte (phosphoenolpyruvate, PEP) concentrations. There was an approximate 25- fold difference in the apparent rate constants for the activation and inhibition phases. This is in contrast to what we háve observed under similar conditions for the C4 enzyme from Zea mays L. for which only inhibition of activity occurs. Spectral studies indicated that up to 7 of the potential 20 histidine residues per subunit were modifíed, at least 3 of which were necessary for activity. The biphasic response of the Crassula enzyme was dependent on the concentration of DEPC. Progressively less inactivation was observed when modifying the enzyme with lower concentrations of DEPC. Chemical modification of PEPC with 75 pM DEPC resulted in a form of the enzyme with a lower K^, and higher This was concomitant with the modification of 4 histidines per subímit. Changes in the response of the enzyme to allosteric effectors were also observed; with modification the enzyme was desensitized to malate inhibition and glucose-6-phosphate activation. The Kj of the modifíed enzyme for malate increased over 15-fold. This was consistent with fluorescence binding studies using the extrinsic conformationalprobe S-anilino-l-naphthalenesulfonate which indicated the elimination of binding of malate and increased binding of the substráte to PEPC. Protection studies showed that malate desensitization was delayed by the presence of malate during modification. Malate also slowed the initial rate of histidine modifícation as measured spectrophotometrically. Thus histidine plays a role in the malate site of Crassula PEPC.
To find the effects of CO2 enrichment on plant development and photosynthetic capacity of nodulated (line A62-1) and non-nodulated (line A62-2) isogenic lines of soybean (Glycine max Merr.), we examined the interactions among two CO2 treatments (36±3 Pa = AC and 70±5 Pa = EC), and two nitrogen concentrations [0 g(N) m-2(land area) = 0N; 30 g(N) m-2(land area) = 30N]. Nodules were found in both CO2 treatments in 0N of A62-1 where the number and dry mass of nodules increased from AC to EC. While the allocation of dry mass to root and shoot and the amount of N in each organ did not differ between the growth CO2 concentrations, there was larger N allocation to roots in 0N than in 30N for A62-2. The CO2-dependence of net photosynthetic rate
(PN) for A62-1 was unaffected by both CO2 and N treatments. In contrast, the CO2-dependence of PN was lower in 0N than in 30N for A62-2, but it was independent of CO2 treatment. PN per unit N content was unaffected by CO2 concentrations. The leaf area of both soybean lines grown in 30N increased in EC. But in 0N, only the nodulated A62-1 showed an increase in leaf area in EC. Nitrogen use efficiency of plants, NUE [(total dry mass of the plant)/(amount of N accumulated in the plant)] in 30N was unaffected by CO2 treatments. In 0N, NUE in EC was lower than in AC in A62-1, and was higher than that at AC in A62-2. Hence, the larger amount and/or rate of N fixation with the increase of the sink-size of symbiotic microorganisms supplied adequate N to the plant under EC. In EC, N deficiency caused the down-regulation of the soybean plant. and T. Nakamura ... [et al.].
Prolamellar bodies (PLBs) isolated from dark-grown, 6.5-d-old leaves of wheat (Triticum aesíivum L. cv. Kosack) were treated with the carboxylic acid cross-linker l-ethyl-3-[3-(diniethylaniino)propyl]carbodiimide (EDC) or with the lysině specific cross-linker 2-iniinothiolane. SDS-PAGE showed that the most prominenent cross- linked product was a dimer of the NADPH-protochlorophyllide oxidoreductase (PCR), but also larger aggregates of the polypeptide were identified by inununological detection on electro-blots. A two-dimensional diagonál gel showed that much of the cross-linking was between the PCR polypeptides. The cross-linkers induced a shift of the fluorescence peak to shorter wavelengths, a bandwidth increase of the fluorescence peak, and an increase of the fluorescence yield. In the presence of NADPH the blue shift was reduced, but the increase in the fluorescence yield still occmred. A cross-linker treatment of PLBs prior to solubilization with 1-0-n-octyl-P -D-glucopyranoside (octylglucoside) delayed, but did not prevent the spectral shifts from 657 to 646 nm and from 646 to 635 nm observed in non-cross-linked detergent- treated PLBs. The cross-linking did not prevent a spectral shift, corresponding to the Shibata shift, of Chlide. Thus the spectral shifts are not strictly coupled to disaggregation of the PCR polypeptides.
DPC played an important role in regulating the production, translocation and partítioning of i‘*C-assimilates in cotton {Gossypium hirsutum L.) plants. Seed soaking with DPC increased the partítioning of cotton assimilates into roots aitd main stem, and decreased the partítioning into seedling tip which was beneficial for the seedling. After the appearance of a square, spraying with DPC decreased the partítioning of assimilates into the main stem, branches and their growing points, and increased the partítioning into reproductíve organs and roots. This helped to avoid or reduce spindling, ensured a steady growth, coordination of the relatíon between vegetatíve and reproductíve organs, and improved the development of floral buds. From bloom to boll-setting,. sprayings with DPC greatly increased the partítioning of assimilates into reproductíve organs and decreased the partítioning into vegetatíve organs, which was usefiil for the growth and development of squares and bolls.
Water-withholding for 5 to 7 weeks and subsequent re-watering were made on potted plants of two epiphytic (E) and two terrestrial (T) fern species, which were collected from a seasonal tropical rainforest and had been grown in a screenhouse with 5 % irradiance for 4 months. During the water stress, the two E species completely closed stomata when frond relative water content (RWC) reached about 70 % with fairly constant maximum photochemistry efficiency (Fv/Fm), while the two T species kept partial stomata opening until RWC reached 45 % and reduction in Fv/Fm at the late stage. Also, chlorophyll content as indicated by a spectral reflectance index was gradually reduced in three species. Physiological recovery was completed after 3-d re-watering for the E species, which was more rapid than for the T species. The gas exchange measurements and regression analyses indicated higher photosynthetic water use efficiency in the E species than in the T species. and Q. Zhang ... [et al.].
The effect of enhanced air CO2 concentrations (C520 and 0^50 = 520 and 650 cm^ m"^) on the growth of Lamium galeobdolon and Stellaria holostea and on the competition between the two species was examined. After five months growth imder CO2 enrichment the dry masses of both species increased when the plants were grown in monoculture, but the increase in biomass was much more pronounced in Stellaria. When the plants were grown together in competition, the measured shoot masses of Stellaria were again higher under C520 and 0^50 than at ambient CO2 concentration (C390 = 390 cm^ m'^), while the shoot masses of Lamium strongly decreased at Cgso- The effect of CO2 enrichment on the two plant species in monoculture differed significantly from that observed in mixed cultures. In terms of plant relative yield, Stellaria benefitted slightly but insignificantly from competition, while Lamium was significantly suppressed imder c^sq. Total community production of the mixed culture was optimum at C520, while that of the monocultures was highest at c^sq. At C390 and C520, growth of Stellaria depended strongly on irradiance in all types of culture. At C650 no such dependence could be demonstrated.
In morphological and biochemical studies we demonstrated that the development of eight-day old dark-grown beán seedlings was drastically influenced by prolonged irradiation with far red (FR) irradiation. The synthetic processes associated with leaf expansion were fiilly active, but the accumulation of chJorophyll (Chl) was very slow and the development of the photosynthetic apparatus was much prolonged. The capacity for oxygen evolution and photophosphorylation began at about the 2''‘* day. Low temperature spectroscopy showed the accumulation of three Chl a forms with absorption maxima at 670, 677 and 683 nm from the veiy beginning of the greening process and the appearance of two longer wavelength forms (with maxima at 690 and 698 nm) at the onset of photosynthetic activity. Electron microscopy showed unfiised stacks of primary thylakoids without grana formation. When the FR treated seedlings were subsequently placed in "white light", grana differentiated from these primary thylakoids.