Respiration begins when a seed absorbs water. The enzymes inside seeds have to be in suspension to function. Activated enzymes start respiration and use organic matter stored in the seed during respiration to make ATP molecules needed for growth. Respiration continues in the seed after the sprout has emerged until the seed’s endospermic material is used up and the cotyledons have produced the sprout.
What is True Respiration?
Respiration is a catabolic reaction that breaks down glucose and other nutrients. Germinating seeds take in oxygen from the surrounding air. The oxygen is used to convert nutrients stored in the seed’s endosperm into energy that the seed uses to sprout. Enzymes activated when the seed imbibes (takes in water) make the energy conversion possible. Carbon dioxide is given off as a waste product during respiration.
Soaking seeds before planting has been a common practice and seeds need water uptake to begin respiring. Dry seeds do respire, but at an extremely low, nearly undetectable rate. Stored gases in seeds are released when water is first taken up. This is not true respiration. True respiration starts when the seed’s testa (seed coating) is softened by water and enough water passes the softened coating to activate seed enzymes. The seed swells and begins to consume oxygen. “H2O2 acts as a signalling molecule,” says scientist Jianhua Xang of Hong Kong Baptist University.
Is Respiration Steady?
Respiration goes in spurts, like seedling growth. A root and a shoot develop as the result of the biochemical reactions in the seed. Seed respiration levels off after this point. When the root and shoot begin the next growth spurt leading up to true leaves, the respiration rate increases again to fuel the growth.
Factors Affecting Respiration
Respiration is affected by storage conditions. Injury or infection during storage makes seeds less able to respire. The germination environment also affects the rate of seed respiration. Adequate respiration depends on several factors, including light exposure, temperature, moisture, oxygen level and carbon dioxide level. These are called abiotic factors because they are nonliving parts of the seeds’ surroundings. An unfavourable environment during the first stage of respiration, when seeds take up water, strongly influences the rate of respiration during the rest of the seeds’ growth. An unfavourable environment inhibits respiration and can cause seed death or spindly seedlings.
When Does Respiration End?
When the young plant has sprouted and begun to grow the first set of true leaves, respiration slows. Seed respiration ends when the seed’s resources have been used up by the new seedling.