The germination characteristics of phytochrome‐deficient aurea mutant tomato seeds

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Abstract
The germination of tomato (Lycopersicon esculentum Mill.) cv. Moneymaker seeds of a phytochrome‐deficient aurea (au) mutant and its isogenic wild types were investigated. In contrast to the wild type whose seeds germinate in darkness, those of the au mutant have a low dark germination level. Continuous far‐red light (FR) inhibits the germination of the wild type, whereas in au‐mutant seed batches exhibiting some dark germination, no inhibition of these dark‐germinating seeds was observed. Germination of the au mutant was promoted by continuous red light (R). Intermittent pulses of R were also effective and phytochrome was implicated as the photoreceptor, since cyclic treatments of 2 min R/2 min FR/26 min darkness led to a significantly lower germination than the control receiving 2 min R/28 min darkness. Germination of the au mutant in darkness increased with the period of post‐harvest storage in paper packers at laboratory temperature. Germination could also be induced in darkness at 25°C by treatment of the imbibed seeds for a period of time at a lower or higher temperature. Germination was also promoted by the presence of nitrate ions in the imbibition medium. In this case simultaneous irradiation with FR failed to inhibit germination of the au mutant, whilst germination of the wild‐type controls was strongly inhibited. In the case of a highly dormant au seed batch where continuous R, low temperature treatment and nitrate ions were partially effective (promotive), full germination could be induced by the combination of continuous R with one of the other factors. The stable pool of phytochrome is predicted to be the pool involved in the promotion of seed germination in darkness as a result of residual Pfr being present in it during dehydration. The au‐mutant seeds are more dormant than wild type seeds and therefore require more of the active FR‐absorbing form of phytochrome (Pfr) to achieve germination. Since the au mutant exhibits a phytochrome‐controlled promotion of germination, it must contain phytochrome and it is speculated that this is stable pool of phytochrome which has been demonstrated to be present in the light‐grown au mutant plants.