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Title: Effects of altered levels of expression of β-carotene hydroxylase on xanthophyll cycle pool size and stress tolerance of rice (Oryza sativa L.)
Author: Zhao, Liang
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2016
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Plants have varied biochemical and physiological responses to excessive light to optimise photosynthesis and to protect their photosynthetic apparatus against photooxidative stress. An important mechanism which protects plant photosystems from light-dependent damage by harmless thermal dissipation of the excitation energy is defined as non-photochemical quenching (NPQ). Extensive studies have shown that the formation and relaxation of qE, the major component of NPQ, are regulated by the xanthophyll cycle (XC, the reversible inter-conversion between the carotenoids violaxanthin and zeaxanthin) as well as pH gradient across thylakoid membrane (ApH) and PsbS protein. Studies using Arabidopsis overexpressing gene (chyB) encoding (3- carotene hydroxylase have shown possibilities to manipulate the kinetics of NPQ and therefore photoprotection by altering the XC pool size. We characterised the changes of xanthophyll cycle pool size, carotenoids composition and NPQ induction in ChyB overexpressing (OE) transformants of rice and compared with ChyB defective (RNAi) and the wild type plants. The XC pool size had nearly twofold increase in the overexpressing plants without affecting the functioning XC, compared to greatly reduced size of XC pool in the ChyB RNAi plants. Accordingly, ChyB OE plants had enhanced capacity of maximal qE and faster formation of qE in comparison with the wild type, while ChyB RNAi plants present retarded qE formation and inferior qE capacity. However, ChyB OE plants showed slow formation of DES (de-epoxidation state of the XC pool) associated with the enlarged XC pool size. Under high light and high temperature conditions, ChyB OE also showed improved resistance to photooxidative stress while ChyB RNAi showed increased sensitivity to photooxidative stress. To investigate the effects of altered XC pool size on modulating NPQ. two types of environment were imposed where light was fluctuating: firstly in a glasshouse (natural rapidly fluctuating light environment) where complete rice canopies were formed. Second in a CE growth chamber experiments where LED lights imposed an artificial growth condition where light continually fluctuated between limitation and saturation. In both environments ChyB RNAi plants also showed inferior growth and biomass production and we conclude that the formation of xanthophyll-dependent NPQ is vital for optimal growth in a variable light environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available