Low growth temperatures modify the efficiency of light use by photosystem II for CO₂ assimilation in leaves of two chilling-tolerant C₄ species, Cyperus longus L. and Miscanthus [multiplication] giganteus
2006
Farage, Peter K. | Blowers, David | Long, Stephen P. | Baker, N. R. (Neil R)
Two C₄ plants, Miscanthus [multiplication] giganteus and Cyperus longus L., were grown at suboptimal growth temperatures and the relationships between the quantum efficiencies of photosynthetic electron transport through photosystem II (PSII) (PSII operating efficiency; F[subscript q][prime]/F[subscript m][prime]) and CO₂ assimilation ([straight phi][subscript CO2]) in leaves were examined. When M. [multiplication] giganteus was grown at 10 °C, the ratio of the PSII operating efficiency to [straight phi][subscript CO2] increased relative to that found in leaves grown at 14 and 25 °C. Similar increases in the F[subscript q][prime]/F[subscript m][prime] : [straight phi][subscript CO2] occurred in the leaves of two C. longus ecotypes when the plants were grown at 17 °C, compared to 25 °C. These elevations of F[subscript q][prime]/F[subscript m][prime] : [straight phi][subscript CO2] at low growth temperatures were not attributable to the development of anthocyanins, as has been suggested for maize, and were indicative of the operation of an alternative sink to CO₂ assimilation for photosynthetic reducing equivalents, possibly oxygen reduction via a Mehler reaction, which would act as a mechanism for protection of PSII from photoinactivation and damage. Furthermore, in M. [multiplication] giganteus grown at 10 °C, further protection of PSII was effected by a 20-fold increase in zeaxanthin content in dark-adapted leaves, which was associated with much higher levels of non-photochemical quenching of excitation energy, compared to that observed in leaves grown at 14 and 25 °C. These differences may explain the long growing season and remarkable productivity of this C₄ plant in cool climates, even in comparison to other C₄ species such as C. longus, which occur naturally in such climates.
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