Lysenko, E. A. | bioRxiv Science

bioRxiv2023

Changes of Cd content in chloroplasts are mirrored by the activity of photosystem I, but not by photosystem II.

Cd is one of the most toxic heavy metals and widespread pollutant. We searched for a direct Cd action on the photosynthetic electron transport chain using induced chlorophyll fluorescence and P700 light absorption. Young barley and maize plants were treated with Cd in toxic (80 M) and nearly lethal (250 M) concentrations. The maximal and relative photochemical activities of PSI, its major limitation at the donor side, and partially acceptor-side limitation of PSII changed in agreement with Cd accumulation in the corresponding chloroplasts. Probably, acceptor-side limitation of PSII increased with a direct Cd action under 80 M that was overcome with an indirect Cd action under 250 M. These alterations can be explained by Cd/Cu substitution in plastocyanin. The photochemical and non-photochemical quenching by PSII varied diversely that cannot be explained unambiguously by any mechanism. The limitations of PSI (Y(ND), Y(NA)) and PSII (qC) were compared for the first time. They were ranged as follows: Y(NA) < qC < Y(ND). Short segments of qC and Y(ND) dynamics varied proportionally to each other. This implies the existence of an unknown mechanism adjusting limitations at the acceptor side of PSII (qC) and at the donor side of PSI (Y(ND)). HighlightsO_LIPSI activity changed in agreement with the changes of Cd content in chloroplasts C_LIO_LIThe data on PSII activity cannot be clearly explained by Cd action C_LIO_LIPSII acceptor-side limitation qC was governed by opposed direct and indirect Cd actions C_LIO_LIPSI and qC changes can be explained by Cd/Cu substitution in plastocyanin C_LIO_LILimitations qC of PSII and Y(ND) of PSI changed proportionally for a short time C_LI

plant biology↗

bioRxiv2022

Lower air humidity reduced both the plant growth and activities of photosystems I and II under prolonged heat stress.

The warming is global problem. In natural environments, a heat stress is accompanied with a drought usually. The effect of lower air humidity remains obscure. Maize and barley plants were supplied with an unlimited source of water for the root uptake and undergone to heat stress for 48 h at contrast conditions of air humidity. The lower air humidity decreased photochemical activities of photosystem I and photosystem II. The small effect was revealed in control. The temperature elevation to 37{degrees}C and 42{degrees}C increased relative activities of the both photosystems; the photosystem II was activated more. The effect of air humidity disappeared at 37{degrees}C; at 42{degrees}C, the effect was small. At 46{degrees}C, lower air humidity magnified substantially the inhibitory effect of heat. Consequently, the maximal and relative activities of the both photosystems were decreased in maize and barley; the plant growth was reduced greatly. The photosystem II was inhibited more. At 46{degrees}C, maize plants increased water uptake by roots at lower air humidity and survived; barley plants were unable to increase water uptake and died. Therefore, air humidity is the important component of environmental heat stress influencing activities of photosystem I and photosystem II and thereby plant growth and viability. HighlightThe effect of severe heat stress was magnified with lower air humidity. At 46{degrees}C, their mutual action inhibited photosystem I and II and reduced greatly the plant growth and viability.

plant biology↗