Germination, precocious

Viviparous mutants of maize provide a second example of an ABA deficiency during grain development affecting germinability. Precocious germination is observed in the viviparous mutants which are deficient in ABA [7,25]. ABA levels in developing maize have also been reduced by treatment of the embryonic tissue with fluridone, which blocks the synthesis of the carotenoid precursors of ABA. The lack of ABA synthesis may explain why fluridone treatment of embryonic tissue between 9 and 13 days post-anthesis inhibited induction of dormancy [7, 20]. 

If immature cotton embryos have the ability to germinate, demonstrated by their behaviour when isolated, why do they not do so in the intact developing seed Vivipary, the germination of immature seeds within the fruit of the parent plant, is rare in cotton and when it occurs it is lethal. Prevention of vivipary might be explained by the fact that coincidental with the capacity of the embryo to germinate precociously, and perhaps to produce messenger RNA for proteinase... 

The concentration of ABA increases in late embryo development shortly before the onset of desiccation and seed dormancy [42,81], ABA inhibits precocious germination of immature embryos in culture [70]. Genetic studies have shown that ABA is involved in dormancy and ABA deficient and ABA-insensitive mutants have been isolated [44]. Reciprocal crosses of wild type and ABA-deficient aba mutants of Arabidopsis showed that there are two different pools of ABA in Arabidopsis seeds. The embryonic ABA is... 

Fig. 1. Precocious germination of seeds of four different genotypes of Arabidopsis thaliana in water under continuous light at 24° C. The seeds were isolated from the fruits at the indicated time, and subsequently transferred to the germination conditions. Germination was counted after 14 days. Seeds developed either in winter or summer...

Application of ABA to immature wheat embryos prevents embryonic germination, while embryo culture without ABA results in precocious germination [23]. Incubation of immature embryos in ABA also causes the early accumulation of proteins that are characteristic of later stages of embryo maturation [22]. Some of the maturation proteins have been identified and these include wheat germ... 

Table 3.5. Development of proteinase enzyme activity during precocious germination of cotton embryos...

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