Net photosynthetic rate (PN) of tobacco plants grown with NH4-N as the only N source was the lowest all the times, while PN grown only with NO3-N was the greatest until 22nd day, and PN grown with both NO3-N and NH4-N (1 : 1) was the greatest. Maximal photochemical efficiency of photosystem 2 (PS2), Fv/Fm, and actual quantum yield of PS2 under actinic irradiation (ΦPS2) in plants grown with only NH4-N were greatest at early stage and then decreased and were smaller than those of other treatments. Photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qNP) in the NH4-N plants were the greatest at all times. Hence excessive NH4-N can decrease not only photochemical efficiency but also the efficiency of utilization of photon energy absorbed by pigments for photosynthesis. Therefore, excessive NH4-N is a hindrance to photosynthesis of flue-cured tobacco. On the other hand, tobacco cultured with an appropriate mixture of NO3-N with NH4-N can sufficiently utilize photon energy and increase the efficiency of energy transformation. and H. X. Guo, W. Q. Liu, Y. C. Shi.
We investigated responses of chloroplasts from flag leaves of a newly-developed super-high-yield rice (Oryza sativa L.) hybrid LiangYouPeiJiu (LYPJ) to water stress (withholding irrigation) during the grain-filling period. In the early stage of water stress (0-6 d) only the activity of Hill reaction was inhibited, whereas activities of photophosphorylation and Ca2+-ATPase, and ATP content were increased and peaked in the day 6 of withholding irrigation. In the late stage of water stress (6-12 d), the activities of photosynthetic O2 evolution, Hill reaction, photophosphorylation, and Ca2+- ATPase, and ATP content were significantly reduced. The membrane lipid content was sharply decreased, especially of sulfoquinovosyl-diacylglycerol (SQDG) and phosphatidylglycerol (PG). The changes in the ultrastructure of chloroplasts included mainly a decrease in number of grana and increase in number of osmiophilic granules. and G.-X. Chen ... [et al.].
The effect of drought on plant water relations and photosynthesis of Vigna glabrescens (Vg) and Vigna unguiculata (cvs. 1183, EPACE-1 and Lagoa), which differ in their drought resistance, was compared. With the increase of drought severity, Vg showed a more gradual stomatal closure and maintained significantly higher levels of stomatal conductance (gs) and photosynthetic activity (PN) than the other genotypes even when minimum relative water content (RWC) values were observed. Furthermore, Vg was the only genotype able to accumulate significant amounts of proline already under moderate water deficit, what could explain the lower osmotic potential (ψs) values observed in these plants. The three V. unguiculata cultivars presented a similar stomatal control under increasing water deficit. A mesophyllic impairment of photosynthetic capacity (Pmax) was detected for cv. 1183 from the beginning of drought onset (85-75 % RWC) while in the Vg plants the values remained unaffected along the whole drought period, indicating that PN decrease observed in this genotype is mainly a consequence of stomatal closure. Such Pmax maintenance suggests the existence of a high mesophyllic ability to cope with increasing tissue dehydration in Vg. and P. Scotti Campos ... [et al.].
The effects of drought stress induced by polyethylene glycol, PEG (molecular mass 6000) on some ecophysiological characteristics of two wild pistachio species, Mastic and Khinjuk (P. mutica and P. khinjuk) selected as root stocks for production of edible pistachio trees (P. vera) in Iran and Turkey, were studied. Net photosynthetic rate (PN), stomatal conductance (gs), chlorophyll (Chl) fluorescence parameters, leaf water potential (Ψ1), leaf osmotic potential (Ψπ), leaf osmotic adjustment (ΔΨπ), and Chl a and b were measured. All parameters were influenced by increase in concentra-tion of PEG in the nutrient solutions. PN, gs, and Chl a were significantly higher in P. mutica than in P. khinjuk but, compared to the control treatment, P. khinjuk showed a higher resistance to drought stress than P. mutica. and A. Ranjbarfordoei ... [et al.].
Drought stress has multiple effects on the photosynthetic apparatus. Herein, we aimed to study the effect of drought stress on fluorescence characteristics of PSII in leaves of Plectranthus scutellarioides and explore potentially underlying mechanisms. Plants of P. scutellarioides were grown in a greenhouse and subjected to drought (DS, drought-stressed) or daily irrigation (control group). Leaf chlorophyll (Chl) index and induction kinetics curves of Chl a fluorescence and the JIP-test were used to evaluate effects of drought lasting for 20 d. Our results showed that both the leaf and soil relative water content decreased with increasing treatment duration. The leaf Chl index was reduced to half in the DS plants compared with the control group after 20 d. The minimal fluorescence in the DS plants was higher than that in the control plants after 10 d of the treatment. Maximum photochemical efficiency and lateral reactivity decreased with increasing treatment duration in the DS plants. With the continuing treatment, values of absorption flux per reaction center (RC), trapped energy flux per RC, dissipated energy flux per RC, and electron transport flux per RC increased in the earlier stage in the DS plants, while obviously decreased at the later stage of the treatment. In conclusion, drought stress inhibited the electron transport and reduced PSII photochemical activity in leaves of P. scutellarioides., L.-L. Meng, J.-F. Song, J. Wen, J. Zhang, J.-H. Wei., and Seznam literatury
The present study aimed to determine effects of drought stress on Lycium ruthenicum Murr. seedlings. Our results showed that mild drought stress was beneficial to growth of L. ruthenicum seedlings. Their height, basal diameter, crown, leaf number, stem dry mass, leaf and root dry mass increased gradually when the soil water content declined from 34.7 to 21.2%. However, with further decrease of the soil water content, the growth of L. ruthenicum seedlings was limited. After 28 d of treatment, the seedlings were apparently vulnerable to drought stress, which resulted in significant leaf shedding and slow growth. However, growth was restored after rehydration. Drought treatments led to a decrease in contents of chlorophyll (Chl) a, b, and Chl (a+b) and increase in the Chl a/b ratio. After rewatering, the Chl content recovered to the content of the control plants. Under drought stress, minimal fluorescence and nonphotochemical quenching coefficient increased, thereby indicating that L. ruthenicum seedlings could protect PSII reaction centres from damage. Maximum fluorescence, maximum quantum yield, actual quantum yield of PSII photochemistry, and photochemical quenching decreased, which suggested that drought stress impacted the openness of PSII reaction centres. A comparison of these responses might help identify the drought tolerance mechanisms of L. ruthenicum. This could be the reference for the planting location and irrigation arrangements during the growing period of L. ruthenicum., Y.-Y. Guo, H.-Y. Yu, D.-S. Kong, F. Yan, Y.-J. Zhang., and Obsahuje bibliografii
Five-year-old trees of deciduous Quercus robur L., evergreen Q. ilex L., and their semideciduous hybrid, Q. × turneri Willd. (var. pseudoturneri), growing in pots, were subjected to drought stress by withholding water for 18-22 days, until leaf water potentials decreased below -2 MPa. Gas-exchange rates, oxygen evolution, and modulated chlorophyll (Chl) fluorescence measurements revealed that by strong stomata closure and declining photosynthetic capacity down to approximately 50%, all three taxa responded with strongly reduced photosynthesis rates. In Q. robur, photochemical quenching of the drought-stressed plants was much lower than in nonstressed controls. Dissection of the occurring events in the photosynthetic electron transport chain by fast Chl fluorescence induction analysis with the JIP-test were discussed. and S. Koller, V. Holland, W. Brüggemann.
Effects of ectopic pacing on left ventricular repolarization were studied in six anesthetized open-c hest chickens. In each animal, unipolar electrograms were acquired from as many as 98 sites with 14 plunge needles (seven transmural locations between epicardium and endocardium in each needle). Activation-recovery intervals (ARIs), corrected to the cycle length, were used for estimating repolarization. At baseline, the nonuniform ARI distribution in the left ventricle resulted in the apicobasal differences being greater than the transmural gradient. Nonuniform ARI prolongation caused by ectopic pacing resulted in decreasing the transmural repolarization gradient and increasing the differences in th e apex-to-base direction. The basal, but not apical transmural differences contributed to the total left ventricular transmural gradient. The total left ventricular apicobasal gradient was contribute d by the apicobasal differences in mid-myocardial and subendoc ardial layers more than in subepicardial ones. Thus, in in situ chicken hearts, the transmural and apicobasal ARI gradients exist within the left ventricle with the shortest ARIs in the basal subepicardium and the longest ARIs in the subendocardium of th e apical and middle parts of the left ventricle. Apicobasal compar ed to transmural heterogeneity of local repolarization properties contributes more to the total left ventricular repolarization gradient., S. N. Kharin, D. N. Shmakov, N. A. Antonova., and Obsahuje bibliografii
Pyrococcus furiosus is a hyperthermophilic archaeon. Its ribulose-1,5-bisphosphate carboxylase/oxygenase (PfRubisco) has only large subunit (L). PfRubisco has a novel (L2)5, decameric structure and it possesses higher carboxylase activity and thermotolerance. To assess the potential functionality of PfRubisco in higher plants under high-temperature stress, PfRubisco coding sequence was transiently expressed in Nicotiana benthamiana by Pea early browning virus mediated ectopic expression. The transgenic PfRubisco plants produced chlorotic yellow stripes in their leaves. Relative to the control leaves, those with yellow stripes exhibited decreased net photosynthetic rate and chlorophyll content, altered chloroplast ultrastructure, and more severe photoinhibition of both photosystem I and II. We concluded that the ectopic expression of PfRubisco might disrupt the chloroplast development and function in N. benthamiana. The potential cause of the disruption was discussed. and X. -G. Li ... [et al.].
The interactive effect of elevated CO2 (EC) and moisture stress (MS) on Brassica juncea cv. Pusa Bold was studied using open-top chambers. The EC markedly increased net photosynthetic rate and internal CO2 concentration and reduced variable and maximal chlorophyll fluorescence. Under MS, EC increased water potential and relative water content, and reduced transpiration rate. The greater allocation of biomass to the roots, which serve as a strong sink for assimilated carbon under EC, helped in better root growth. and B. K. Rabha, D. C. Uprety.