Reduced Metabolic Activity:
Dormant seeds exhibit a significant reduction in their metabolic rate compared to actively growing plants. This is achieved by decreasing the overall activity of various enzymes involved in cellular respiration. As a result, the seed consumes less oxygen and produces less carbon dioxide.
Alternative Electron Transport Pathways:
The electron transport chain, where most ATP synthesis occurs during cellular respiration, may undergo modifications in dormant seeds. Alternative pathways, such as the alternative oxidase (AOX) pathway, become more prominent. AOX allows for the transfer of electrons directly to oxygen without going through the entire electron transport chain, minimizing energy loss and reactive oxygen species (ROS) production.
Enhanced Antioxidant Defense:
Dormant seeds often accumulate high levels of antioxidants, such as ascorbic acid (vitamin C), tocopherols (vitamin E), carotenoids, and flavonoids. These antioxidants help protect cellular components, including enzymes involved in cellular respiration, from oxidative damage caused by ROS.
Regulation of TCA Cycle:
The tricarboxylic acid (TCA) cycle, also known as the Krebs cycle, plays a crucial role in cellular respiration. In dormant seeds, the activity of certain enzymes in the TCA cycle may be altered to reduce the production of intermediates used in anabolic processes. This allows the seed to divert resources towards energy storage molecules.
Glyoxylate Cycle Activation:
Some dormant seeds activate the glyoxylate cycle, which functions alongside the TCA cycle. The glyoxylate cycle enables the conversion of fatty acids, stored as triglycerides, into carbohydrates. This alternative pathway helps the seed mobilize stored reserves and generate energy without complete degradation of lipid molecules.
Storage of Carbohydrates:
Instead of consuming all the energy produced during cellular respiration, dormant seeds store a significant portion of it as carbohydrates, mainly in the form of starch or sucrose. This energy storage strategy ensures the seed has readily available reserves for germination and early seedling growth.
Maintenance of ATP Levels:
Dormant seeds maintain relatively low levels of ATP, just enough to sustain essential cellular processes and repair mechanisms. ATP production is tightly regulated to minimize energy expenditure and prevent damage from excessive ROS production.
Overall, the modifications of cellular respiration in dormant seeds contribute to their remarkable ability to withstand harsh environmental conditions, maintain cellular integrity, and remain viable for extended periods until favorable conditions for germination occur.
