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Zhou W.-H.,Gansu Agricultural University | Zhou W.-H.,Ministry of Education Key Laboratory of Ecosystem Gansu Province Laboratory of Pratacultural Engineering | Zhou W.-H.,Sino Us Center For Grazingland Ecosystem Sustainability | Shi S.-L.,Gansu Agricultural University | And 5 more authors.
Chinese Journal of Applied Ecology | Year: 2012

In order to explore the regulation approaches for improving the salt-tolerance of alfalfa, the seedlings of Medicago sativa L. cv. Gannong No. 4 were taken to study their growth and nitrogen metabolism under salt stress as affected by NO-donor SNP, NO-scavenger c-PTIO, and sodium ferrocyanide (a SNP analogue with NO not released). Exogenous NO could obviously alleviate the inhibition effects of salt stress on the seedling growth and photosynthesis via increasing plant dry matter and leaf chlorophyll content, net photosynthesis rate, transpiration rate, and soluble protein content. Exogenous NO enhanced the activities of leaf nitrate reductase, glutamine synthetase, and glutamate-oxoglutarate aminotransferase, restrained the activities of protease and glutamate dehydrogenase, decreased the free amino acid content, and improved the nitrate content and ammonium assimilation under salt stress. Applying sodium ferrocyanide did not show any alleviation effect on the seedling growth and nitrogen metabolism under salt stress. As a NO-scavenger, c-PTIO inhibited the growth and nitrogen metabolism under salt stress, but the inhibition effect could be mitigated by supplementing SNP. It was suggested that exogenous and endogenous NO were involved in the regulation of alfalfa nitrogen metabolism under salt stress. Source

Kou J.T.,Gansu Agricultural University | Kou J.T.,Sino Us Center For Grazingland Ecosystem Sustainability | Shi S.L.,Gansu Agricultural University | Shi S.L.,Sino Us Center For Grazingland Ecosystem Sustainability | And 4 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2014

Plant photosynthetic capability usually changes after damage by a herbivorous pest. Photosynthetic compensation is the physiological response of the plant to pest damage with the level of compensation varying with the change in pest damage. This paper explores the photosynthetic response mechanism of alfalfa to the dominant insect-Odontothrips loti -and explains the compensatory mechanism of alfalfa to thrip damage. The thrip resistant clone, R-1 and susceptible clone, I-1 were used to investigate the gas exchange and chlorophyll fluorescence parameter changes under different insect densities (0, 1, 3, 5, and 7 per branch, respectively), Photosynthesis equipment, GFS-3000 (Walz, Germany) and modulated chlorophyll fluorometer imaging-PAM (Walz, Germany) were used. For the 7 per branch treatment, the results indicate that the chlorophyll content of R-1 initially increased and then decreased, while the chlorophyll content of I-1 decreased. For R-1, the chlorophyll content was 11.32% lower than CK (0 thrip per branch), and for the 3, 5, and 7 per branch treatments of I-1, the chlorophyll contents were 14.05%, 22.02% and 26.27% lower than CK, respectively. For both R-1 and I-1, the net photosynthetic rate (Pn) and water use efficiency (WUE) decreased, while the intracellular concentration of CO2(Ci), stomatal conductance (Gs) and transpiration rate (Tr) increased. For R-1, the Pn of 3, 5, and 7 per branch treatments were 6.98%, 19.03% and 20.11% lower than CK, and the WUE of all the treatments were 16.32%, 23.95%, 37.12% and 45.89% lower than CK. For I-1 treatments, the Pn of all the treatments were 5.38%, 8.77%, 22.47% and 35.66% lower than CK, and the WUE were 25.23%, 31.05%, 45.78% and 61.81% lower than CK, respectively. The chlorophyll content, WUE and Pn of R-1 were all greater than I-1 under the same insect density. As insect density increased, the initial fluorescence (F0) increased, which for the R-1 clone resulted in F0 for 5 and 7 per branch treatments of 6.99% and 9.13% higher than CK, respectively. For the I-1 clone, all the treatments were 2.81%, 6.45%, 12.36% and 14.93% higher than CK, respectively. The actual photosynthetic efficiency (ΦPSII) of PSII, non-photochemical quenching coefficient (NPQ), photochemical quenching coefficient (qP), potential activity (Fv/ F0) of PSIIand original light transformation efficiency (ΦPSII) of PSIIdecreased for both R-1 and I-1. Among which the Fv/ F0of 3, 5 and 7 per branch treatments for the R-1 clone were 5.07%, 16.74% and 21.19% lower than CK and the Fv/ Fmof 5 and 7 per branch treatments were 3.50% and 4.63% lower than CK, respectively. For the I-1 clone, Fv/ F0of all the treatments were 8.24%, 13.68%, 22.88% and 28.04% lower than CK, and the Fv/ Fmwere 1.67%, 2.91%, 5.31% and 6.86% lower than CK, respectively. Under the same insect density, R-1 was found to have a lower F0 but higher ΦPSII, qP, Fv/ F0 and Fv/ Fm, when compared with I-1. As a rule, the gas exchange parameter and chlorophyll fluorescence kinetic parameter of R-1 fluctuated less than I-1, indicating that the thrip's rasping-sucking damage had injured the chloroplast tissue of alfalfa leaves, decreased the anabolism of chlorophyll, aggravated leaf transpiration, decreased WUE, and therefore affected alfalfa photosynthesis. The thylakoid membrane in the alfalfa leaves and PSIIreaction center were injured, which decreased the absorption of light energy, and impeded the photosynthetic electron transport, reducing its photosynthetic efficiency. While under lower insect densities (1 per branch, 3 per branch), the R-1 clone had a stronger capability to adjust for water loss and usage after being damaged by the thrip, demonstrating adaptability to the thrip's rasping-sucking damage through internal regulation, lowering PSIIdamage, with higher absorption, transmission, use and conversion efficiency. Therefore the R-1 clone was found to have a stronger resistance to thrips when compared with the I-1 clone, as expressed by the higher photosynthetic efficiency and photosynthetic compensation effect. © 2014, Science Press. All rights reserved. Source

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