The effects of serosally added 5-hydroxytryptamine (5-HT, 100 μM) on the short circuit-current (Isc) across jejunum and ileum taken from fed, starved and undernourished (Gerbillus cheesmani) were investigated. The effects of the neurotoxin, tetrodotoxin (TTX, 10 μM) on the basal Isc as well as on the maximum increase in Isc induced by 5-HT were also studied. There were regional variations in the basal Isc as well as in the way by which the small intestine responds to 5-HT. The basal Isc was greater in jejunum than in ileum and such differences were TTX-sensitive. The maximum increase in Isc, which results from addition of 5-HT, was higher in jejunum than in ileum under all three feeding conditions. TTX reduced the maximum increase in Isc induced by 5-HT across stripped and intact intestine of the two regions in the three nutritional states. The 5-HT-induced Isc in the jejunum of both starved and undernourished gerbils and in the ileum of starved animals was the function of both submucosal and myenteric plexus. In jejunum and ileum taken from starved and undernourished gerbils the 5-HT-induced Isc was both chloride- and bicarbonate-dependent. Thus the results indicated that both starvation and undernourishment increase that response and such increases were TTX-sensitive and both chloride- and bicarbonate-dependent., F. Y. Al-Balool., and Obsahuje bibliografii a bibliografické odkazy
Photosynthetic electron flux allocation, stomatal conductance, and the activities of key enzymes involved in photosynthesis were investigated in Rumex K-1 leaves to better understand the role of nitric oxide (NO) in photoprotection under osmotic stress caused by polyethylene glycol. Gas exchange and chlorophyll fluorescence were measured simultaneously with a portable photosynthesis system integrated with a pulse modulated fluorometer to calculate allocation of photosynthetic electron fluxes. Osmotic stress decreased stomatal conductance, photosynthetic carbon assimilation, and nitrate assimilation, increased Mehler reaction, and resulted in photoinhibition. Addition of external NO enhanced the stomatal conductance, photosynthetic rate, activities of glutamine synthetase and nitrate reductase, and reduced Mehler reaction and photoinhibition. These results demonstrated that osmotic stress reduced CO2 assimilation, decreasing the use of excited energy via CO2 assimilation which caused significant photoinhibition. Improving stomatal conductance by the addition of external NO enhanced the use of excited energy via CO2 assimilation. As a result, less excited energy was allocated to Mehler reaction, which reduced production of reactive oxygen species via this pathway. We suppose that Mehler reaction is not promoted unless photosynthesis and nitrogen metabolism are prominently inhibited. and H. D. Li ... [et al.].
Adenosine is secreted from adipocytes, binds to adenosine A1 receptor and modulates various functions of these cells. In the present study, the effects of an adenosine A1 receptor antagonist (DPCPX; 0.01, 0.1 and 1 μM) on lipogenesis, glucose transport, lipolysis and the antilipolytic action of insulin were tested in rat adipocytes. DPCPX had a very weak effect on lipogenesis and did not significantly affect glucose uptake. In adipocytes incubated with 1 μM DPCPX, lipolysis increased. This effect was blunted by insulin and by a direct inhibitor of protein kinase A. Moreover, 0.1 μM DPCPX substantially enhanced the lipolytic response to epinephrine and increased cAMP in adipocytes. However, DPCPX was ineffective when lipolysis was stimulated by direct activation of protein kinase A. Adipocyte exposure to epinephrine and insulin with or without 0.1 μM DPCPX demonstrated that this antagonist increased the release of glycerol. However, despite the presence of DPCPX, insulin was able to reduce lipolysis. It is concluded that DPCPX had a weak effect on lipogenesis, whereas lipolysis was significantly affected. The partial antagonism of adenosine A1 receptor increased lipolysis in cells incubated with epinephrine alone and epinephrine with insulin due to the synergistic action of 0.1 μM DPCPX and epinephrine., T. Szkudelski, K. Szkudelska, L. Nogowski., and Obsahuje seznam literatury
Arbuscular mycorrhizal fungi (AMF) form symbioses with many plants. Black locust (Robinia pseudoacacia L.) is an important energy tree species that can associate with AMF. We investigated the effects of AMF (Rhizophagus irregularis and Glomus versiforme) on the growth, gas exchange, chlorophyll (Chl) fluorescence, carbon content, and calorific value of black locust seedlings in the greenhouse. The total biomass of the arbuscular mycorrhizal (AM) seedlings was 4 times greater than that of the nonmycorrhizal (NM) seedlings. AMF greatly promoted the photosynthesis of black locust seedlings. AM seedlings had a significantly greater leaf area, higher carboxylation efficiency, Chl content, and net photosynthetic rate (PN) than NM seedlings. AMF also significantly increased the effective photochemical efficiency of PSII and significantly enhanced the carbon content and calorific value of black locust seedlings. Seedlings inoculated with G. versiforme had the largest leaf area and highest biomass, Chl content, PN, and calorific value., X. Q. Zhu, C. Y. Wang, H. Chen, M. Tang., and Obsahuje bibliografii
Brassinosteroids (BRs) have been reported to counteract various stresses. We investigated effects of exogenously applied brassinosteroid, 24-epibrassinolide (EBR), and brassinosteroid-mimic compound, 7,8-dihydro-8α-20-hydroxyecdysone (DHECD), on the photosynthetic efficiency and yield of rice (Oryza sativa L. cv. Pathum Thani 1) under heat stress. Solutions (1 nM) of EBR and DHECD were separately sprayed onto foliage of individual rice plants during their reproductive stage. Five days after the application, the plants were transferred to the day/night temperature regime of 40/30°C for 7 days and then allowed to recover at normal temperature for 7 days. We demonstrated that both DHECD and EBR helped maintain the net photosynthetic rate. The DHECD and EBR application enhanced stomatal conductance, stomatal limitation, and water-use efficiency under the high-temperature regime. DHECD- and EBR-treated plants showed an increase in the nonphotochemical quenching that was lower than that in the control plants. Moreover, DHECD and EBR treatments maintained the maximal quantum efficiency of PSII photochemistry and the efficiency of excitation capture of the open PSII center. Furthermore, the treatments with DHECD or EBR resulted in higher chlorophyll content during the heat treatment compared with the control plants. The paddy field application of 1 nM EBR and/or 1 nM DHECD at the reproductive stage during the hot season could increase the rice yield, especially, the number of filled seeds. DHECD and EBR enhanced total soluble sugar and reducing sugar in straw and more starch was accumulated in rice seeds. Consequently, our results confirmed that DHECD showed biological activities mimicking EBR in the improvement of photosynthetic efficiency and in rising the rice yield under heat stress., J. Thussagunpanit, K. Jutamanee, W. Sonjaroon, L. Kaveeta,
W. Chai-Arree, P. Pankean, A. Suksamrarn., and Obsahuje bibliografii
Ca2+ is an important factor mediating many biotic and abiotic stress responses in plants. In this study, we measured the chlorophyll (Chl) fluorescence of transgenic rice with increased or decreased expression of a calcium-sensing receptor (OsCaS) gene during water deficit caused by polyethylene glycol to prove our hypothesis that increased Ca2+ in combination with increased OsCaS could enhance the drought resistance of transgenic rice. Transcript abundance (evaluated by RT-PCR) was significantly lower in OsCaS antisense line 766 (AS766) than that in the wild type, while the overexpression line 777 (O777) showed four times higher amount than that in the wild type. Chl fluorescence showed that the photochemical quantum yield of PSII in the light increased due to addition of Ca2+ in the O777, but dropped in the AS766. Nonphotochemical quenching increased under stress in both transgenic lines and in the wild type, but less in the O777. Nonregulatory quantum yield of energy dissipation showed no significant change under drought stress. Photochemical quenching was significantly higher in the O777 than those in the AS766 and in the wild type after the Ca2+ treatment. In the absence of stress, the electron transport rate (ETR) was significantly higher in the O777 than in both the AS766 and the wild type. In contrast, the ETR of the wild type and both transgenic lines decreased under drought stress, while the effect of polyethylene glycol was partially alleviated by Ca2+ addition in the O777. In summary, excitation energy conversion and dissipation by PSII were regulated by Ca2+ in the O777. It might partially alleviate the effect of drought stress, whereas addition of Ca2+ had no effect in the wild type and the AS766., R. Wei, Y. Liu, Y. Sui, M. Xu, S. Liu, X. Zhao., and Obsahuje seznam literatury
Heavy metals such as cadmium (Cd) may affect different physiological functions in plants. We carried out a hydroponic experiment under greenhouse conditions in order to evaluate the effect of Cd on photosynthetic and physiological parameters of safflower. The responses of six safflower genotypes (Nebraska-10, 2811, Kouseh, S149, C111, and K12) to four concentrations of CdCl2 (0, 1.5, 3, and 4.5 mg L-1) were examined. Mean shoot and root dry masses of safflower plants were reduced by nearly 57% after the treatment by 4.5 mg(CdCl2) L-1. Contrary to the mean proline content, which increased by 121%, the mean total leaf area per plant, net photosynthetic rate, stomatal conductance to the CO2, leaf chlorophyll a, b, and (a+b), carotenoid content, and quantum efficiency of PSII decreased by 84.4, 50.5, 50.0, 31.6, 32.2, 31.8, 32.9, and 11.2%, respectively, at the presence of 4.5 mg(CdCl2) L-1. The mean Cd concentration in shoots and roots of safflower genotypes exhibited 52- and 157-fold increase, respectively, due to the addition of 4.5 mg(CdCl2) L-1 to the growing media. The mean malondialdehyde content was enhanced by 110% with the increasing CdCl2 concentration, indicating the occurrence of a considerable lipid peroxidation in the plant tissues. Even though the membrane stability index was adversely affected by the application of 1.5 mg(CdCl2) L-1, the decrease ranged from 45 to 62% when plants were treated with 4.5 mg(CdCl2) L-1. Genotype Nebraska-10 seemed to be different from the remaining genotypes in response to the 4.5 mg(CdCl2) L-1; its net photosynthetic rate tended to be the greatest and the Cd concentration in shoots and roots was the lowest among genotypes studied. This study proved Cd-induced decline in growth, photosynthesis, and physiological functions of safflower., L. Moradi, P. Ehsanzadeh., and Obsahuje seznam literatury
Two greenhouse experiments were conducted in order to investigate the effects of different levels of water stress on gas exchange, chlorophyll fluorescence, chlorophyll content, antioxidant enzyme activities, lipid peroxidation, and yield of tomato plants (Solanum lycopersicum cv. Jinfen 2). Four levels of soil water content were used: control (75 to 80% of field water capacity), mild water stress (55 to 60%), moderate water stress (45 to 50%), and severe water stress (35 to 40%). The controlled irrigation was initiated from the third leaf stage until maturity. The results of
two-year trials indicated that the stomatal conductance, net photosynthetic rate, light-saturated photosynthetic rate, and saturation radiation decreased generally under all levels of water stress during all developmental stages, while compensation radiation and dark respiration rate increased generally. Water stress also declined maximum quantum yield of PSII photochemistry, electron transfer rate, and effective quantum yield of PSII photochemistry, while nonphotochemical quenching increased in all developmental stages. All levels of water stress also caused a marked reduction of chlorophyll a, chlorophyll b, and total chlorophyll content in all developmental stages, while activities of antioxidant enzymes, such as superoxide dismutase, peroxidase, and catalase, and lipid peroxidation increased., X. K. Yuan, Z. Q. Yang , Y. X. Li, Q. Liu, W. Han., and Obsahuje seznam literatury
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