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. 1985 Mar;77(3):676–686. doi: 10.1104/pp.77.3.676

Control of Seed Germination by Abscisic Acid 1

III. Effect on Embryo Growth Potential (Minimum Turgor Pressure) and Growth Coefficient (Cell Wall Extensibility) in Brassica napus L.

Peter Schopfer 1, Claudia Plachy 1
PMCID: PMC1064584  PMID: 16664118

Abstract

The physical mechanism of seed germination and its inhibition by abscisic acid (ABA) in Brassica napus L. was investigated, using volumetric growth (= water uptake) rate (dV/dt), water conductance (L), cell wall extensibility coefficient (m), osmotic pressure (∏i), water potential (Ψi), turgor pressure (P), and minimum turgor for cell expansion (Y) of the intact embryo as experimental parameters. dV/dt, ∏i, and Ψi were measured directly, while m, P, and Y were derived by calculation. Based on the general equation of hydraulic cell growth [dV/dt = Lm/(L + m) (Δ∏ - Y), where Δ∏ = ∏i - ∏ of the external medium], the terms (Lm/(L + m) and ∏i - Y were defined as growth coefficient (kG) and growth potential (GP), respectively. Both kG and GP were estimated from curves relating dV/dt (steady state) to ∏ of osmotic test solutions (polyethylene glycol 6000).

During the imbibition phase (0-12 hours after sowing), kG remains very small while GP approaches a stable level of about 10 bar. During the subsequent growth phase of the embryo, kG increases about 10-fold. ABA, added before the onset of the growth phase, prevents the rise of kG and lowers GP. These effects are rapidly abolished when germination is induced by removal of ABA. Neither L (as judged from the kinetics of osmotic water efflux) nor the amount of extractable solutes are affected by these changes. ∏i and Ψi remain at a high level in the ABA-treated seed but drop upon induction of germination, and this adds up to a large decrease of P, indicating that water uptake of the germinating embryo is controlled by cell wall loosening rather than by changes of ∏i or L. ABA inhibits water uptake by preventing cell wall loosening. By calculating Y and m from the growth equation, it is further shown that cell wall loosening during germination comprises both a decrease of Y from about 10 to 0 bar and an at least 10-fold increase of m. ABA-mediated embryo dormancy is caused by a reversible inhibition of both of these changes in cell wall stability.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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