Preconditioning and germination of Orobanche seeds: Respiration and protein synthesis

Abstract

The imbibition and respiration of Orobanche seeds during preconditioning and germination are described. Fully imbibed seeds show two peaks in respiration, followed by a gradual decline in the absence of stimulant. In the presence of stimulant two peaks are also discerned, one during the preconditioning and one during the germination period, which are followed by a gradual decline after the seeds germinate. Drying the seeds after preconditioning results in the non-appearance of the second respiratory peak and a slow decline in respiration. The drop following germination can probably be ascribed to exhaustion of substrate, but the decline in absence of germination stimulant must have other causes. Seeds take up and metabolize radioactive leucine both during preconditioning and germination. Part of the leucine is respired. The pattern of proteins present in the seeds shows distinct changes both during preconditioning and during germination. In addition, after 8 hr of preconditioning, a number of proteins are synthesized. Towards the end of the germination period, fewer new proteins are formed. In the absence of germination stimulant, incorporation of label into protein gradually declines with time and fewer new proteins are synthesized. The results clearly show that seeds which are not exposed to a germination stimulant are able to remain viable for considerable periods of time without damage. In contrast, seeds which start to germinate but do not reach a host show clear indications of exhaustion of their reserve materials and probably will die.