Klaus, A. A. | Search bioRxiv

bioRxiv2026

Common excluder barley has more than one mechanism to remove Cd from chloroplasts

Chloroplasts comprise photosynthesis and other important processes. Plants protect chloroplasts from stresses including Cd accumulation. Common terrestrial plants, excluders apply a set of mechanisms to restrict Cd penetration to chloroplasts. Removal of accumulated Cd from chloroplasts should also be a beneficial strategy. However, we do not know whether excluder plant species have ability to remove Cd from chloroplasts. We used barley as a common excluder plant species. To barley plants, we applied a model with two stable isotopes 111Cd and 114Cd to distinguish Cd accumulated earlier and later. A portion of Cd absorbed by roots continued translocation to shoot for some days after the external source of Cd was changed from one isotope to another. Chloroplasts acquired new portions of Cd and lost part of Cd accumulated earlier; a total Cd content remained rather unchanged. Cd loss from thylakoids was detected in vivo and in vitro. Cd loss from stroma and envelope was observed in vivo but not in vitro. Therefore, barley has at least two distinct mechanisms for Cd removal from chloroplasts: one from thylakoids and another from stroma. We hypothesized diverse chlorophagy pathways as a potential mechanism for Cd removal from chloroplasts. Cd accumulation by chloroplasts was mainly light-independent. In chloroplasts, Cd accumulated in vivo was tightly bound and mainly located in thylakoids. In vitro, chloroplasts from Cd-treated plants accumulated much less Cd than chloroplasts from untreated plants in a previous study. This implies reorganization of transport across chloroplast envelope membranes. HighlightsO_LICd was removed from thylakoids both in vivo and in vitro C_LIO_LICd was removed from stroma and envelope in vivo but not in vitro C_LIO_LIIn chloroplasts, Cd accumulated in vivo was tightly bound C_LIO_LICd accumulation by chloroplasts was mainly light-independent C_LIO_LIRoot barrier slowed down Cd translocation to shoot but not halted it 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↗