Embryo germination

There are two types of receptor, termed fast and slow sites [21]. The fast responses (detectable in <5 min) appear to be brought about by membrane-mediated phenomena, while the slow responses, which involve protein synthesis, are not detectable within the first half hour. The receptor types have different molecular requirements, and the fast reaction is not a pre-requisite for the slow. Growth assays employed to assess activity include Avena coleoptile, lettuce hypocotyl, rice seedling, and bean axis. Other types include lettuce seed and wheat embryo germination, transpiration assays, leaf disk senescence, and more recently, a-amylase production. Stomatal closing using epidermal strips is an assay for the fast receptor. 

Finally, another important hormonal factor (but not the last) is the abscisic acid (ABA). This compound is produced mainly in chloroplasts. Its main functions are stomata closure, seed dormancy and the inhibition of axiUaiy buds growth. The addition of ABA to in vitro embryogenic cultures inhibits the early embryo germination and stimulates the coordinated maturation of the somatic embryo. However, prolonged exposition to ABA, this element suppresses growth of the formed in vitro plants (Bozhkov et al., 2002). 

In this chapter we describe a stable and efficient plant regeneration system for the Hinoki and Sawara cypress via somatic embryogenesis. The initiation of embryogenic cultures (EC), their maintenance and proliferation, maturation of somatic embryos, germination... 

Hay, E.I. and Charest, P.J. (1999) Somatic embryo germination and desiccation tolerance in conifers. In Somatic Embryogenesis in Woody Plants, Vol. 4. Jain, S.M. et al. (ed), 547 pp, Kluwer Academic Publishers, Dordrecht, 61-%. 

In the megagametophyte of gymnosperms DNA content varies but slightly during embryo germination, e.g. Pseudotsuga menziesii [32], Pinus resinosa [107] and P. nigricans [12]. 

Examples of Epicotyl and Hypocotyl Dormancy. It is particularly well-known of our Rosaceae that their seeds require vernalization. In the case of the apple it has been found (Fig. 203) that if the seed coat is removed germination still does not take place. If, however, the thin endosperm pellicle is also removed, the embryos germinate. (We have already mentioned that the endosperm of the Rosaceae is impermeable to gases and that, for example, hydrogen cyanide formed after water uptake cannot escape.) The seedlings of other Rosaceae as well as the apple show. 

Figure 9.4 Photographs from the breeding programme developed at IMIDA-ITUM. (a) Rescued embryos germinating in vitro (b) bunch of Itumsix (c) bunch of Itumseven (d) plot of Itumflve (e) plot of Itumtwuelve.

Raw Materials. Two principal types of malting-grade badey are in use, ie, six-row and two-row. Six-row badey has six kernels around the stalk, whereas the two-row variety has two kernels. Six-tow kernels tend to be twisted, and the two-row grade is more symmetrical. Figure 1 is an illustration of a badey kernel and its key components. As badey is converted into malt, the acrospire for the embryo lengthens until it reaches the far end of the kernel, and roodets also grow as if the seed is germinating into a new plant. A discussion of the stmcture and composition of badey can be found in Reference 1. 

Cucurbit seeds are exalbuminous or lacking endosperm in the mature state. In such seeds the embryo is large in relation to the seed as a whole. It fills the seed almost completely and its body parts, particularly the cotyledons, store the food reserves for germination. Since the predominant tissue of the seed is cotyledonous, and since cotyledons are leaves, anatomy and histology of typical leaf tissue suffice to describe the preponderant part of the seed. Epidermal cells cover the cotyledonary surface followed by palisade and abundant parenchyma cells that contain the food reserves. Vascular tissues are also present. 

The cerebral endothelial cells of the blood-brain barrier originate from the middle germinal sheet of the embryo, the mesoderm [17]. Concomitant with migration and proliferation of capillary endothelial cells during formation of the cerebral vascular network occurs the imprinting of the cells. Thereby, induction by the cellular surrounding plays an important role [18-21], The relevance of the cellular environment for the development of the barrier function of cerebral microvessels was first demonstrated by Stewart and Wiley [22], who transplanted embryonic brain tissue of a quail into embryonic gut tissue of chicken and vice versa. The cerebral transplant was vascularized by intestinal vessels, in which properties of the blood-brain barrier had been induced. In transplanted brain vessels, however, no characteristics of a barrier could be demonstrated, due to the lack of a neuronal environment. These results indicated that the cerebral microvessels are of extraneuronal origin, with properties that are induced by the cellular environment. In addition, brain tissue has the capability to induce blood-brain barrier characteristics also in noncerebral vascular tissue [23],... 

A developing embryo produces ABA, which incepts and maintains mature seed dormancy. Germination begins with the uptake of water by imbibition of the dry seed and is followed by embryo expansion. Usually, it is considered complete when the radicle is through all the covering layers. There is still controversy whether... 

The methylation of DNA at CpG islands has also turned out to be an important regulator for cell development, the differentiated proteome and the regulation of cell survival [237,238]. Indeed the implications of this chemical modification have been linked to DNA accessibility, chromatin fluidity and cell transformation [239,240]. DNA methylation is required for genomic stability and believed to act as an inert epigenetic marker in germinal cells and preimplantation embryos [238]. Presumably, DNA methylation is required for the heritable transmission of chromatin structure, which prevents the expression of terminally silenced genes in differentiated tissues, and provides a host-defense mechanism against parasitic transposable elements [241]. 

Extracts (12 mL each) were added to Petri dishes 10 cm in diameter containing 50 g of 30-mesh washed sand covered with filter paper circle (7-cm diameter, Whatman 1). Controls were moistened with doubly distilled water. Ten indicator seeds were placed on the filter paper in each dish with the embryo down and the hypocotyl pointed to the center of the Petri dish. Each indicator/extract combination had 3 replicates. The Petri dishes were kept in a dark growth chamber for approximately 72 hr at 25°C. The radicle length of each germinated seedling was measured at 72 hr. 

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