Heat-induced down-regulation of photosystem II protects photosystem I in honeysuckle (Lonicera japonica)

Photochemical Efficiency of Photosystem II in Inverted Leaves of Soybean [Glycine max (L.) Merr.] Affected by Elevated Temperature and High Light

“…Under natural conditions, a combination of high light and heat stress in summer is the main environmental stress that leads to a decrease in plant photosynthesis, usually starting with a reduction in the production of photosynthetic assimilates under mild abiotic stress when leaves avoid water dissipation by reducing stomatal aperture and thus limiting the mesophyll conductance to CO 2 , at which point diffusive limitation is the main cause of the decrease in leaf photosynthetic capacity (Das et al, 2015;Bahamonde et al, 2018;Fanourakis et al, 2019;Mihaljević et al, 2020). As the stress level increased and time increased, the leaf photosynthetic apparatus was damaged and PSII photochemical activity was reduced in addition to diffusive limitation, and at this time, the nondiffusion limitation was better than diffusion limitation (Hazrati et al, 2016;Jiang et al, 2021). In this study, the P n and gs of inverted leaves and normal leaves…”

“…The PI ABS values of normal and inverted leaves decreased by 63.2%-66% and 68%-90% at 4 p.m., respectively, compared to 9 a.m. Compared with PI ABS , the PI total values not only reflect PSII photosynthetic electron transfer activity but also relate to changes in PSI-related processes (Kalaji et al, 2014;Jiang et al, 2021). Therefore, some researchers suggest that PI total is more sensitive to abiotic stresses than PI ABS .…”

“…Under natural conditions, a combination of high light and heat stress in summer is the main environmental stress that leads to a decrease in plant photosynthesis, usually starting with a reduction in the production of photosynthetic assimilates under mild abiotic stress when leaves avoid water dissipation by reducing stomatal aperture and thus limiting the mesophyll conductance to CO 2 , at which point diffusive limitation is the main cause of the decrease in leaf photosynthetic capacity ( Das et al, 2015 ; Bahamonde et al, 2018 ; Fanourakis et al, 2019 ; Mihaljević et al, 2020 ). As the stress level increased and time increased, the leaf photosynthetic apparatus was damaged and PSII photochemical activity was reduced in addition to diffusive limitation, and at this time, the nondiffusion limitation was better than diffusion limitation ( Hazrati et al, 2016 ; Jiang et al, 2021 ). In this study, the P n and gs of inverted leaves and normal leaves were significantly reduced at 4 p.m. during the treatment, and C i of normal leaves was also significantly reduced at noon, but C i in inverted leaves behaved differently in both years, with no significant difference between 9 a.m. and 4 p.m. C i in inverted leaves in 2020, while the difference reached a significant level in 2021, which could be caused by climatic factors between years but could at least suggest that the reduction in P n of normal leaves can be explained by a reduction in gs ( Pandey et al, 2007 ) and that inverted leaves may be more susceptible to photooxidative damage and damage to the photosynthetic apparatus at elevated temperature and high light compared to normal leaves, which is supported by the decrease in F v /F m values and performance indexes (PI ABS and PI total ) and the increase in DI O /RC values in inverted leaves at noon.…”

“…Many studies have assessed the harmful effects of heat on photosynthesis, where elevated temperatures reduce CO 2 fixation by inhibiting photosynthetic system activity. The inactivation of PSII in plants under complex stress in summer leads to a decrease in photosynthetic capacity ( Fanourakis et al, 2019 ; Jiang et al, 2021 ). Some researchers have noted that F v /F m values of normal leaves range from 0.75 to 0.83 and that a decrease in this parameter indicates that PSII has been damaged ( Krause and Weis, 1991 ).…”

“…Under natural conditions, the elevated temperatures at noon in summer are usually accompanied by other environmental stresses, such as high light, and the dual stress of heat and high light seriously affects the growth and development of soybeans, especially during the seed-filling stage, resulting in reduced soybean yields ( Cohen et al, 2021 ; Kimm et al, 2021 ). As an important organ in direct contact with the environment, leaves are more sensitive to light and temperature, because photosystem II (PSII) is sensitive to heat and high irradiation stress during the process of carbon dioxide assimilation ( Dongsansuk et al, 2013 ; Jiang et al, 2021 ). Exposure to high light and elevated temperature in summer can damage the photosynthetic apparatus of the plant and cause photoinhibition, which is manifested in the metabolic processes: reduced transpiration accompanied by increased leaf temperature, reduced antioxidant and photosynthetic enzyme activities, damage to the cytoplasmic membrane, destruction of chloroplast structure and function, reduced electron transport and carbon metabolism, and increased reactive oxygen species (ROS) ( Janka et al, 2013 ; Gu et al, 2017 ; Blackhall et al, 2020 ; Mihaljević et al, 2020 ).…”