Mechanisms Regulating the Dynamics of Photosynthesis Under Abiotic Stresses

Abstract

Photosynthesis sustains plant life on earth and is indispensable for plant growth and development. Factors such as unfavorable environmental conditions, stress regulatory networks, and plant biochemical processes limits the photosynthetic efficiency of plants and thereby threaten food security worldwide. Although numerous physiological approaches have been used to assess the performance of key photosynthetic components and their stress responses, though, these approaches are not extensive enough and do not favor strategic improvement of photosynthesis under abiotic stresses. The decline in photosynthetic capacity of plants due to these stresses is directly associated with reduction in yield. Therefore, a detailed information of the plant responses and better understanding of the photosynthetic machinery could help in developing new crop plants with higher yield even under stressed environments. Interestingly, cracking of signaling and metabolic pathways, identification of some key regulatory elements, characterization of potential genes, and phytohormone responses to abiotic factors have advanced our knowledge related to photosynthesis. However, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. Here, we provide a detailed overview of the research conducted on photosynthesis to date, and highlight the abiotic stress factors (heat, salinity, drought, high light, and heavy metal) that limit the performance of the photosynthetic machinery. Further, we reviewed the role of transcription factor genes and various enzymes involved in the process of photosynthesis under abiotic stresses. Finally, we discussed the recent progress in the field of biodegradable compounds, such as chitosan and humic acid, and the effect of melatonin (bio-stimulant) on photosynthetic activity. Based on our gathered researched data set, the logical concept of photosynthetic regulation under abiotic stresses along with improvement strategies will expand and surely accelerate the development of stress tolerance mechanisms, wider adaptability, higher survival rate, and yield potential of plant species.

Keywords: abiotic stresses; biosynthesis; chlorophyll; degradation; photosynthetic machinery.

Figure 1

Schematic representation of the photosynthesis performance under abiotic stresses (heat, drought, and salinity). Drought and heat stress down-regulate enzymatic activity and electron transport chain (ETC) and cause membrane rupture, low CO₂ solubility, leaf senescence, and reactive oxygen species (ROS) production. On the other hand, salinity causes ion toxicity, membrane disruption, reduced stomatal conductance, lower quantum yield of PSII, slow electron transport, and reduced activity of photosynthesis related enzymes.

Figure 2

Diagram showing the general and specific effects of heavy metals on plants. Heavy metals affect ROS production, inhibit ATP synthesis and damage DNA and proteins. The damage to DNA and proteins is shown separately. Free radicals damage DNA and cause membrane peroxidation when metal ions surround the site of tissue injury, causing ATP inhibition, and NADH depletion.

Figure 3

Heavy metal stress damages the chloroplast structure and chlorophyll (Chl) biosynthesis and degradation processes during photosynthesis. Toxicity due to metal ions gradually affects enzymatic activity and inhibits Chl components and the uptake of essential elements, finally blocking the Chl biosynthesis pathway. The blue arrow depicts this process in a step-by-step manner.

Figure 4

Regulation of the complex phytohormone network under stress conditions. The imposition of stress on the photosystem reaction center induces the hormonal signal transduction. The red dotted lines indicate the regulation of two hormone inhibitions, and green lines indicate the co-regulation of two hormones. The regulation of gene transcription by different hormones shows the involvement of the photosynthetic machinery.