The emphasis of modern dormancy research is almost entirely on the form of dormancy that is acquired during seed development, primary dormancy. Abscisic acid (ABA) appears to be intimately involved in its regulation. The action of abscisic acid has also been implied in many other developmental processes. The coincidence of developmental events, such as dehydration and completion of maturation, with the acquisition of primary dormancy suggests that dormancy is influenced by these processes. Germinability, both during development and after maturation, is sometimes directly correlated with ABA content. The lack of such a correlation may be explained by assuming a decisive role for the responsiveness to ABA or other overriding factors. ABA has been detected in all seed components. The different seed tissues may all contribute, to various extents, to the degree of whole seed dormancy. It is concluded that ABA action in dormancy regulation is not restricted to the embryo but is also located in endospermic tissue. In addition, a role of ABA in the morphological development of germination modifying seed tissues is proposed. The mechanism for ABA action appears to be associated with cell wall properties.

It has been proposed that sucrose and raffinose play a role in the storability of maize seeds. The levels of these sugars in the embryos and the glassy state were compared in maize seeds of contrasting storage stability to determine the relationship between sugar composition, glassy state and the storability of the seed. Sucrose was the predominant sugar but its content was not correlated with good storage. The content of raffinose as a mass fraction of total sugars and the magnitude of the glassy state showed positive correlations with storage stability. It is suggested that in maize seeds dry storage stability is a reflection not of the total soluble sugars, but of the mixture of sucrose with raffinose. Apparently raffinose amplifies the magnitude of the glass signal and this in turn is associated with enhanced storability.

In the present study, the efficiency of two cryopreservation strategies for oil palm (Elaeis guineensis Jacq.) was compared. If extracted from rehydrated kernels, 65% of the embryos desiccated to around 0.3 g H2O/g DW developed into plantlets after cryopreservation. In contrast, only 25% of embryos (0.12 g H2O/g DW) extracted from cryopreserved dry kernels developed into plantlets. However, this value was increased to 63% if kernels were partially rehydrated before freezing until the water content of embryos reached 0.3 g H2O/g DW. This study emphasizes the importance of partial rehydration of oil palm embryos before cryopreservation.

Imbibed embryos of after-ripened and secondarily thermo- and FR-dormant Agrostemma githago seeds were investigated as to their ability to synthesize DNA, RNA and proteins with the aim of finding characteristic differences connected with the induction and maintenance of developmental arrest. A gradual decrease in DNA synthesis was observed during the induction of thermodormancy. However, DNA synthesis was stimulated up to that of embryos of 30–h-imbibed after-ripened seeds within 24 h approximately after transferring the thermodormant seeds into temperatures which normally allow germination. DNA synthesis of embryos of FR-dormant seeds remained constant at a relatively low level during 7 d FR and another 7 d dark incubation. RNA synthesis decreased to different extents during induction of thermo- and FR-dormancy when it was arrested at a relatively low level in seeds transferred to temperatures which normally allow germination. Processes leading to an increase in RNA synthesis such as in embryos of after-ripened seeds appeared to be quantitatively and/or qualitatively repressed. Interestingly, protein synthesis was extremely depressed during induction of thermodormancy whereas it was slightly stimulated during induction of FR-dormancy. Nevertheless two-dimensional protein PAGE revealed several polypeptides which were new, increased, decreased or not synthesized predominantly in axes of thermo- and FR-dormant seeds in comparison to germinating after-ripened seeds. It is suggested that a connection exists between these polypeptides and the repression of germination. After transferring seconarily dormant seeds to temperatures which normally allow germination, a temporary stimulation of protein synthesis could be observed in both cases.

Seed germination of the hemiparasitic angiosperm Striga hermonthica is elicited by compounds present in the root exudates of the host plant. A variety of chemicals can substitute for the host-derived signal although the exact mechanism through which these act is unknown. In the present study, thidiazuron (TDZ), a cytokinin-active urea derivative was found to stimulate germination. This thidiazuron-induced germination was shown to be mediated by endogenous ethylene, by a similar mechanism to germination induced by host-root exudate and the synthetic stimulant GR-24. Comparing the effects of TDZ, host-root exudate, GR-24 and the ethylene precursor 1-aminocyclopropane-1-car-boxylic (ACC) suggests that ethylene production increases as a result of increased ACC synthesis and is consistent with a model for Striga seed germination in which host-derived signals and other stimulants act by eliciting the synthesis of ethylene via a stimulation of ACC synthase activity. All germination stimulants tested trigger a rapid increase in O2 uptake by conditioned seeds. The patterns of O2 uptake following TDZ or GR-24 treatments show similarities and three distinct phases of respiration are apparent. In contrast, stimulation of O2 uptake by ethylene results in a different pattern, with no distinct phases obvious following the initial burst of activity.

Experiments were performed to determine if RAPD profiles developed using total DNA isolated from soybean seed could be affected by the physiological state or the quality of the seed. RAPD profiles were developed using template DNA isolated from a single seed lot of soybean (Glycine max L. cv. Kirby). High quality seeds were used to produce four populations varying in either quality or physiological state: untreated control seed ambient temperature and humidity storage for 12 months, accelerated aging at 41°C and 100% relative humidity for 48 h, and controlled hydration (seed priming). One hundred and eighty-eight primers were used to create separate RAPD profiles from total DNA isolated from each set of seed and from soybean leaf tissue. Sixteen polymorphisms from 14 primers were identified as a result of seed treatments. Six primers showed nine polymorphisms in RAPD profiles of ambient-stored seed DNA, while four and two primers produced polymorphisms in reactions using accelerated aged or primed-seed template DNA, respectively. Two primers showed a polymorphic fragment in vegetative DNA not observed in any of the seed DNA samples. Ten of the observed polymorphisms were due to the appearance of a DNA fragment in response to a specific seed treatment while six were the result of the treatment-induced loss of a DNA fragment. The six polymorphisms resulting from the loss of a major fragment were all due to ambient-temperature seed storage. Results were reproducibly obtained from multiple DNA isolations using three separate DNA isolation procedures involving either multiple seed or a single seed as the template source. Therefore, genetically identical seed can consistently display RAPD polymorphisms as a response to the environmental exposure.

An element of storage stability of many orthodox seeds is that the embryo cytoplasm is vitreous at normal storage temperatures. That is, as drying proceeds during seed maturation, intracellular solutions become so concentrated and viscous that diffusional movement is all but eliminated (Williams and Leopold, 1989). In this report the relationship between desiccation tolerance and the ability to form the vitreous state as germination proceeds is examined. As pea seeds (Pisum sativum cv. Alaska) imbibed water up to 18 h, no change in the glass transition temperature was seen, and the embryos remained desiccation-tolerant. Between 18 and 44 h of imbibition, the axes lost the ability to exhibit a distinguishable vitreous transition, and the embryos had lost the ability to survive desiccation. After about 50 h, embryos again showed vitrification but only at markedly lower temperatures, as would be expected to accompany the loss of oligosaccharides (sucrose, raffinose, stachyose and verbascose) and their replacement by monosaccharides during early germination (Koster and Leopold, 1988). Thus, the loss of desiccation tolerance during germination in pea seeds appears to be associated with a loss of the high temperature oligosaccharide: water glass and a subsequent appearance of a new glass transition at a lower temperature resulting from the accumulation of monosacchrides.

The endosperm and cotyledon tissues of Ricinus communis seeds and young seedlings were examined for changes in the mineral nutrient composition of globoids during early seedling growth. The effect on globoid composition of providing mineral nutrients to the developing seedling was also investigated. Globoids in endosperm and cotyledon tissues of castor bean seeds contained P, Mg and K, as well as trace amounts of Ca, Fe and Zn. Irrespective of the addition of mineral nutrients, K content in globoids of endosperm and cotyledon tissues declined significantly during initial seedling growth. During early seedling growth, amounts of Fe, Zn and Ca increased in cotyledon globoids. Ca contents of globoids of endosperm tissues also increased. The changes in Fe, Zn and Ca globoid contents were not influenced by providing mineral nutrients to growing castor bean seedlings.