The effect of several inorganic salts on the dark germination inducing action of gibberellin was studied using 10 to 29 months stored tobacco seeds as plant materials. Gibberellin was added to the germination beds in very low concentrations; in these concentrations gibberellin itself could not induce dark germination in high rate.
When the pH of the germination beds were controled with HCl-KOH, HCl-NH₄OH and HNO₃-KOH, two pH optima were observed at pH ranges between 2.0 and 3.0, and between 4.8 and 5.5. In these cases, the first pH optima moved to more acidic sides and there the germination rates reached higher values, as the storage length of the seeds increased. On the contrary, at the second pH optimum, the germination rates decreased remarkably to the levels of the controls, when the storage period of the seeds became longer.
When H₃PO₄-KOH was used for pH adjustment, three pH optima were obseved. In these cases, at the first pH optimum (pH2.2-2.7), the germination rate seemed to increase following the lengthening of the storage period. In the second and third pH optima (around 4.0 and 5.0), however, the germination rates seemed to decrease with the increase of the storage length. When H₃PO₄ and NH₄OH were used as pH adjusters, four pH optima were observed. In this case first and second optima (pH2.0 and around 3.0) seemed to correspond to the first one of the previous case.
It was observed in all the cases, that at around pH5.0 the seed having shorter storage length had higher germination rate than the longer one.