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Regulation of guard cell photosynthetic electron transport by nitric oxide

2013; Oxford University Press; Volume: 64; Issue: 5 Linguagem: Inglês

10.1093/jxb/ers397

1460-2431

Attila Ördög, Barnabás Wodala, Tamás Rózsavölgyi, Irma Tari, Ferenc Horváth,

Plant responses to elevated CO2

Nitric oxide (NO) is one of the key elements in the complex signalling pathway leading to stomatal closure by inducing reversible protein phosphorylation and Ca2+ release from intracellular stores. As photosynthesis in guard cells also contributes to stomatal function, the aim of this study was to explore the potential role of NO as a photosynthetic regulator. This work provides the first description of the reversible inhibition of the effect of NO on guard cell photosynthetic electron transport. Pulse amplitude modulation (PAM) chlorophyll fluorescence measurements on individual stomata of peeled abaxial epidermal strips indicated that exogenously applied 450nM NO rapidly increases the relative fluorescence yield, followed by a slow and constant decline. It was found that NO instantly decreases photochemical fluorescence quenching coefficients (qP and qL), the operating quantum efficiency of photosystem II (ΦPSII), and non-photochemical quenching (NPQ) to close to zero with different kinetics. NO caused a decrease in NPQ, which is followed by a slow and continuous rise. The removal of NO from the medium surrounding the epidermal strips using a rapid liquid perfusion system showed that the effect of NO on qP and ΦPSII, and thus on the linear electron transport rate through PSII (ETR), is reversible, and the constant rise in NPQ disappears, resulting in a near steady-state value. The reversible inhibition by NO of the ETR could be restored by bicarbonate, a compound known to compete with NO for one of the two coordination sites of the non-haem iron (II) in the QAFe2+QB complex.