Germination gibberellins

In addition to inhibitory chemicals which enter the plant from the external environment, many endogenous inhibitors appear to function as regulators of seed germination and plant growth and development. The interrelationships between endogenous inhibitors and growth promoters such as the auxins, gibberellins, and kinins remain to be elucidated. 

ABA produce more mature seeds showing primary dormancy than the wild-type plants. A reduced dormancy often occurs in seeds of ABA-insensitive mutants. Gibberellin A (GA) is absolutely required for germination of the wild-type Arabidopsis seeds. Seeds of ethylene-insensitive and GA-insensitive mutants are supersensitive to exogenous ABA, which suggests that in imbibed seeds ethylene and GA may directly counteract the action of ABA in dormancy maintenance. ... 

Results. The analytical data are summarized in Table II. Absorption of the gibberellin from its solution is more nearly complete at the lower concentration range, and the applied material is relatively little degraded during germination and drying. The data clearly indicate translocation of gibberellin into the sprouts. 

Figure 3. Germination of lettuce and Lepidium seeds held in darkness at 25° and 20° C., respectively, after moistening with various concentrations of gibberellin A3, dissolved in unbuffered or dilute citrate phosphate buffer...

The increased germination was not the direct effect of pH alone or of the one particular buffer. Phthalate-HCl, glycine-HCl, and sodium aconitate buffers at pH 3.2 had no effect in the dark but did increase the sensitivity of seed to light. Germination in darkness occurred only when the acid or a buffered solution of gibberellin was used to moisten the substrate. 

In the germination of cereal seeds, it was long known by brewers that if the embryo was excised (or dead) the endosperm would not be hydrolyzed and sugars would not be released. In 1960, Paleg showed that amylolytic activity in the embryo-less half could be fully restored in the presence of gibberellin. In other words, the substance that passed from the embryo to the endosperm (or rather, to the living cells of the aleurone layer that encloses the dead endosperm) induces there the synthesis of a-amylase which is responsible for hydrolysis of the stored starch reserves held in the endosperm. The extent to which the a-amylase was induced became another bioassay for gibberellin. 

Interconversion of gibberellin A2o to gibberellin A29 by etiolated seedlings and germinating seeds of dwarf Pisum sativum." Phytochemistry, 197, 13, 793-796. 

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