Photosynthesis and Heat Stress

Heat Stress and Photosynthesis

• Heat stress and oxidative stress can prevent the healing of damaged PSII by inhibiting PSII protein production, leading to a reduction in plant photosynthesis efficacy.
• Chlorophyll, the principal photosynthetic component, can absorb light energy and facilitate electron transport in the early and most critical phases of photosynthesis.
• Under heat stress, the amount of chlorophyll in leaves declines, resulting in leaf senescence or chlorosis.
• Thermal treatment raises the efficiency of chlorophyllase and Chl-degrading peroxidase, leading to a significant drop in Chl levels.

Oxidative Damage

• Plant responses to heat stress accumulate ROS, including singlet oxygen, superoxide radical, hydrogen peroxide, and hydroxyl radical, causing oxidative damage.
• The activation sites of PSI and PSII in chloroplasts are primary locations of ROS formation, although ROS is produced in other organelles such as peroxisomes and mitochondria.
• The maximum efficacy of PSII and the acquired ROS have a linear relation.
• Heat stress has been proposed as a primary source of ER stress.

Heat Stress Responses and ROS Homeostasis

• ROS are produced by enzymatic and nonenzymatic processes in plants under normal and stressful situations and are linked to several stages of plant development and growth.
• Heat stress triggers the release of ROS scavengers, which eliminate excessive ROS.
• ROS scavengers in plants include Ascorbate peroxidase (APX), Catalase (CAT), CSD1, CSD2, and CCS1.
• Heat stress induces the release of cell wall binding protein Expansin 1 (AsEXP1) in hair grass, involved in cell wall remodeling.

Heat Stress Responses and Epigenetic Modifications

• Epigenetic modifications occur at the DNA level in response to heat stress.
• Epigenetic modifications, including DNA methylation, histone modifications, histone variations, short RNAs, and long noncoding RNAs, may upregulate to defend plants from destruction.
• These modifications are related to heat stress response (HSR) gene expression.
• The activation of methyltransferases has been examined extensively in response to heat stress.

Cell Membrane Disruption

• Plants that thrive at high temperatures retain permeability and stability, necessitating membrane fluidity variability.
• Thylakoids and cell membranes are usually one of the first to be altered by high thermal effects.
• Heat stress causes the decomposition of the structural proteins of the cellular membrane, leading to membrane permeability and disruption of cellular functions.