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

Abstract

AbstractNon-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°C), while increased it under nearly lethal heat stress (46°C). Usually, limitation at the acceptor side of the photosystem I was minor, while at 46°C it appeared major limiting factor. A similar decrease of photosystem II activity at 46°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°C and more reduced at 42-46°C. In barley, the decrease had complex pattern: the size of flashes greatly reduced at 37°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.HighlightsLight 1s induces instant limitations at acceptor-sides of PSII (qC) and PSI (Y(NA))Temperature reduced these flashes of qC and Y(NA) proportional to each otherThe pattern of reduction was different in barley and maizeFlash of qC was quenched by proportional flash of qN in barley but not in maizeStationary PSII activity was decreased by different mechanisms in barley and maize