Respiration of Germinating Seeds

Low levels of respiration have been reported in dry seeds, though we mean dry in a relative sense since such seeds do contain moisture, e.g. cereal grains in dry storage have a 10-15% water content. Respiration of stored seeds will be discussed further in the second volume of this book during our consideration of viability and longevity. 

Seed and fruit coats can act as barriers to the uptake of water and thus prevent or retard germination. They can also affect respiration by limiting the permeability to oxygen. Coat effects on germination and the restriction of gaseous exchange is another topic reserved for the second volume. 

The introduction of dry seeds to water results in an immediate and rapid evolution of gas, an event which may last for several minutes. This burst upon wetting is not related to respiration the gas is not predominantly CO2, and could be that released from colloidal adsorption as water is imbibed. Further, this release occurs from dead seeds and non=-living seed parts [54]. 

A very early metabolic event during imbibition, occurring in less than 15 min, appears to be the reformation of keto acids from amino acids by deamination and transamination reactions [37]. Keto acids important for respiratory pathways (e.g. a-ketoglutarate and pyruvate) may be absent from dry seeds such as wheat [70] and peanut cotyledons [138]. They are known to be chemically unstable and it has been suggested [37] that they are stored in the dry seed as the appropriate amino acid, and then reformed on rehydration. This might occur also in barley embryos, seeds of Sinapis alba, and axes and cotyledons of Phaseolus vulgaris [36, 37]. 

Phase /. This is characterized by a sharp rise in respiration lasting about 10 h and is attributed in part to activation and hydration of mitochondrial enzymes associated with the citric acid cycle and electron transport chain (see 

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