Differences between barley and maize revealed in limitations of photosystems I and II under high temperature and low air humidity.

Abstract

Non-photochemical quenching and limitations of the photosystem I and photosystem II activities were studied in C3-plant barley and C4-plant maize. Plants were undergone to prolonged heat stress under high and low air humidity. Both species decreased non-photochemical quenching under tolerated heat stress (37-42{degrees}C), while increased it under nearly lethal heat stress (46{degrees}C). Usually, limitation at the acceptor side of the photosystem I was minor, while at 46{degrees}C it appeared major limiting factor. A similar decrease of photosystem II activity at 46{degrees}C by lower air humidity was achieved through different mechanisms. In barley, photosystem II downregulated by the increase of non-photochemical quenching. In maize, photosystem II downregulated by the increase of limitation at the acceptor side. Analysis of transients also revealed differences between species. One second after a light induction, limitations flashes at the acceptor sides of both photosystems. Elevating temperature reduced the size of these flashes; acceptor-side limitations of both photosystems decreased proportional to each other. In maize, the decrease was simple: the size of flashes slightly decreased at 37{degrees}C and more reduced at 42-46{degrees}C. In barley, the decrease had complex pattern: the size of flashes greatly reduced at 37{degrees}C and gradually returned to the control level under the higher temperatures. Around the photosystem II, the flash was quenched by a later burst of non-photochemical quenching. In barley, the transient peaks of acceptor-side limitation and non-photochemical quenching were very similar at any temperature. This was not observed in maize. The ratios between limitations qC/Y(NA) and qC/Y(ND) were studied. HighlightsO_LILight 1s induces instant limitations at acceptor-sides of PSII (qC) and PSI (Y(NA)) C_LIO_LITemperature reduced these flashes of qC and Y(NA) proportional to each other C_LIO_LIThe pattern of reduction was different in barley and maize C_LIO_LIFlash of qC was quenched by proportional flash of qN in barley but not in maize C_LIO_LIStationary PSII activity was decreased by different mechanisms in barley and maize C_LI