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The Regulation Of Light Harvesting In The Photosynthetic Apparatus Of Plants

Posted on:2008-05-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y ChenFull Text:PDF
GTID:1100360215455072Subject:Botany
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In the light-fluctuating environment plants have developed some strategies coping with the changes in the sunlight. Amongthese strategies the regulation of light harvesting of the photosynthetic aparratus is very important to maximize utilization at low light and avoid photodamage at high light.The dissociating of some light-harvesting complex (LHCII) from photosystem II (PSII) core complexes is probably a regulatory way dealing with short-term high light.The study on the LHCII dissociation mayt assist to understand the mechanisms of light-harvesting regulation and photoprotection. This work mainly explores its evidence,universality and the difference between it and state transition. The main results are as follows.1 The gas exchange evidence for reversible dissociation of light-harvesting complex LHCIIPlants often regulate the amount and size of LHC II to maximize photosynthesis at low light and avoid photodamage at high light. In this study gas exchange, 77K chlorophyll fluorescence and PSII electron transport as well as LHCII protein were measured in leaves illuminated by different light in intensity. The obtained results were as follows. After irradiance transition from saturating to limiting one leaf photosynthetic rate in soybean leaves declined first to a low level, then rose slowly to a stable value (V pattern), while in wheat leaves it dropped immediately to a stable value (L pattern). Saturating pre-irradiation led to significant declines in both 77K fluorescence parameter F685/F735 and light-limited PSII electron transport rate in soybean but not in wheat leaves, indicating that some LHCIIs dissociate from PSII in soybean but not in wheat leaves. Moreover, L pattern of the LHCII-decreased rice mutant and V pattern of its wild type also demonstrate that V pattern is linked to dissociation/re-association of some LHCIIs from/to PSII. 2 Species-dependence of light-harvesting complex LHC II dissociationThrough the observing and calculating of leaf photosynthetic responses to changes in light intensity and CO2 concentration it was found that among the examined more than 50 plant species 32 species and residual 25 species showed respectively the V pattern and L pattern of the photosynthetic response curve to light intensity transition. The species-dependence of the photosynthetic response pattern was not related to classification in taxology because the photosynthetic response to light intensity transition might display the two different patterns (V and L) in plants of the same family, for example, rice and wheat (Gramineae), soybean and peanut (Leguminosae). It seemed to be related to the pathway of photosynthetic carbon assimilation. All of the examined C4 plants (maize, green bristlegrass and thorny amaranth) displayed the L pattern in the photosynthetic response to light intensity transition. It might be related the light environment where plants originated. The V pattern of photosynthetic response to light intensity transition was often observed in some plants grown in shade habitats, for example, sweet viburnum and japan fatsia, while the L pattern was frequently observed in those plants grown in sun habitats, for example, ginkgo and cotton. Furthermore, the ratio of electron transport rate to carboxylation rate in vivo measured at limiting light in V pattern plants (mostly higher than 10) was far higher than that in L pattern plants (mostly lower than 5), but the ratio measured at saturating light had no differencebetween the two kind plants. These results can be explained by that the V pattern plant species have larger light-harvesting complex (LHCII) and at saturating light the reversible dissociation of some LHCIIs from PSII reaction center complex occurs. The pattern of photosynthetic response to light intensity transition and the ratio of electron transport rate to carboxylation rate in vivo measured at limiting light are probably used as probes distinguishing between sun and shade plants.3 Difference between light-harvesting complex LHC II dissociation and state transitionIn order to determine if the saturating light-induced LHCII reversible dissociation is a phenomenon of state transition, the effects of different light treatments on leaf photosynthesis and low temperature (77K) chlorophyll fluorescence parameters were observed in Arabidopsis, soybean and wheat leaves. The main results are as follows. (1) The photosynthetic response curve to light intensity transition from saturating to limiting one in Arabidopsis wild-type leaves was V pattern, while the curve in Arabidopsis mutant leaves lacking chloroplast protein kinase STN7 was L pattern. (2) After illumination with saturating white light 77K fluorescence parameters F685 and F685/F735 decreased significantly in Arabidopsis wild-type, but not in Arabidopsis mutant stn7 leaves. (3) After illumination with weak red light F685 and F685/F735 decreased significantly, F735 increased significantly in Arabidopsis wild-type, but not in Arabidopsis mutant stn7 leaves; (4) both the weak red light and saturating light treatment could induce significant decreases in F685 and F685/F735 without an increased F735 in soybean leaves. (5) Significantly decreased F685, F685/F735 and increased F735 could be induced by weak red light but not saturating white light in wheat leaves. These results indicate that saturating white light can induce the reversible dissociation of some LHCIIs from PSII core complex but not cause the transition from state1 to state 2 in Arabidopsis wild-type and soybean leaves. Also, the transition from state1 to state 2 in Arabidopsis wild-type and wheat leaves can be induced by weak red light but not by saturating white light. Hence, the reversible LHC II dissociation occurred in saturating light-illuminated leaves is not a phenomenon of state transition because the dissociated LHC II is not associated with PS I.
Keywords/Search Tags:light-harvesting comlex of photosystem II (LHCII), low temperature (77K) chlorophyll fluorescence, net photosynthetic rate, PSII electron transport, reversible dissociation, species dependence, state transition, Arabidopsis
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