Contrasting patterns of photosynthetic acclimation to the light environment are dependent on the differential expression of the responses to altered irradiance and spectral quality |
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Authors: | E H Murchie & P Horton |
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Institution: | Robert Hill Institute, Department of Molecular Biology and Biotechnology, Western Bank, University of Sheffield S10 2TN, UK |
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Abstract: | Chl, chlorophyllChl a/b, ratio of chlorophyll a to chlorophyll bCyt f, cytochrome fFR, far-red lightLFR, low irradiance, far-red enriched growth lightLHCII, light harvesting complex associated with PSIILW, low irradiance, white growth lightMW, moderate irradiance, white growth lightPAR, photosynthetically active radiationPmax, light and CO2 saturated photosynthetic ratePSI, photosystem IPSII, photosystem IIFour plant species (Chamerion angustifolium, Digitalis purpurea, Brachypodium sylvaticum and Plantago lanceolata) which have previously been shown to demonstrate contrasting photosynthetic acclimatory responses to the light environment ( 33 , Plant, Cell and Environment 20, pp. 438–448) were analysed at a biochemical level. Plants were grown under low irradiance with a shade-type spectrum (LFR: 50μmol quanta m–2 s–1), moderately high white light (MW: 300μmol quanta m–2 s–1) and low irradiance white light (LW: 50μmol quanta m–2 s–1). The effects of light quality upon chlorophyll content and photosynthetic capacity were found to be species-dependent. A far-red dependent reduction in chlorophyll was found in three species, and an irradiance-dependent reduction was found in B. sylvaticum, which showed the greatest alteration in the xanthophyll cycle pool size of all species tested under these conditions. Chlorophyll a/b ratios were sensitive to both light quality and quantity in C. angustifolium and D. purpurea, being highest in MW, lowest in LFR, and intermediate in LW, whilst the other species showed no response. Ratios of photosystem II to photosystem I (PSII and PSI) demonstrated a strong irradiance-associated increase in all species except B. sylvaticum, whereas an increase in PSII/PSI in LFR compared to LW conditions was present in all species. A change in chlorophyll a/b was not always associated with a change in PSII/PSI, suggesting that the level of LHCII associated with each PSII varied in some species. Cytochrome f content showed an irradiance-dependent effect only, indicating a relationship with the capacity of electron transport. It is concluded that differing strategies of acclimation to the light environment demonstrated by these species results from differing strengths of expression of a series of independently regulated changes in the levels of photosynthetic components. |
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Keywords: | acclimation chloroplast irradiance photosynthesis photosystem spectral quality |
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