Embryonic axis

The seeds of dicotyledonous plants have two cotyledons, or seed leaves, which are part of the embryo. The cotyledons usually are the main storage tissue, although in some plants (such as castor bean) the endosperm also has a storage function. During development in the field, seeds gradually accumulate storage oils, proteins and carbohydrates (Table 3.1). In the seed, the cotyledon structure is relatively simple. The remainder of the embryo, the embryonic axis, consists mostly of undifferentiated cells, but provascular tissue can be detected that develops into vascular tissue in the seedling. 

To date very little is known of the regulation of the gln-a gene. This gene must be expressed strongly during seed development as its mRNA is present at quite high levels in both the cotyledons and embryonic axis of dry seeds and is the predominant or perhaps only GS mRNA present in... 

The greatest portion of the lipids in barley kernel is nonpolar lipids (67-78%). The compositions of lipids in the embryonic axis, bran endosperm, and hull fractions of hulless barley caryopses were determined by Price and Parsons (124) (Table 27). Neutral lipids were predominant in all fractions. Phospholipid content of barley hull was lower than that of the bran endosperm and embryonic axis. The hull fraction contained the highest glycolipid amount among the grain fractions. 

Fatty Acid Embryonic Axis Bran-endosperm Hull Embryonic Axis Bran-endosperm Hull... 

Figure 7.1 Chemical images of the same wheat kernel cross-section showing the population on the z-axis. (a) Lipid in the scutellum and aleurone cell walls (b) Protein in the embryonic axis and aleurone cells ...

Figure 7.3 (a) Sketch of wheat kernel cross-section, showing from the outside towards the center pericarp, aleurone cells, aleurone cell walls, endosperm, depleted layer and germ (scutellum and embryonic axis). The following regions of the kernel were studied A = pericarp/endosperm B = pericarp/ subaleurone endosperm C = corner of germ D = single aleurone cell E = endosperm/ scutellum (b) Cross-section (not to common... 

Figure 7.13 (a) Unsprouted kernel /,y,z chemical functional group maps of (left) scutellum (lipid), (center) embryonic axis (protein) and (right) endosperm (carbohydrate). All images are from the same imaging data cube (b) Sprouted kernel x,Y,z chemical functional group maps of (left)... 

Vasiliauskas, D., Stern, C.D. 2001. Patterning the embryonic axis FGF signaling and how vertebrate... 

In the more benign asexual cycle, Epichloe endophytes (and all Neotyphodium species) remain asymptomatic (Fig. 1). As floral primordia are formed, endophytes grow into ovules, proliferate in the nucellus tissues, and later colonize the embryonic axis of the developing seed, which leads to vertical transmission (Freeman, 1904 Philipson and Christey, 1986). Hyphae in the remnant nucellar layer form a conspicuous mat between the aleuron and the seed coat (White et al., 1991). Symptomless endophytes may also invade stamen filaments and anther walls, but have never been found in pollen grains, and apparently are not disseminated via paternal structures (Sampson, 1933 Hinton and Bacon, 1985). Vertical transmission of endophytes in infected tillers occurs at nearly 100% efficiency (Siegel et al., 1984). However, seeds which are free of endophyte may occasionally be produced when shoot meristems of individual... 

CoUinearity describes the sequential expression of a genomic cluster of Hox genes along an embryonic axis and associated properties. 

Although roots, particularly the root apices, are a major site of cytokinin biosynthesis in plants, there is evidence now that other meristematic tissues and organs including the cambium, developing buds, seeds and fruits and the embryonic axis of germinating seed have the ability to synthesize cytokinins under optimal growth conditions [6, 14]. Recently, stem and leaves have also been shown to be additional sites of cytokinin production [6]. The view that root-produced cytokinins move in the xylem to the shoot to participate in the control of development and senescence is widely accepted [15]. The major question that remains to be clarified is under what conditions the observed cytokinin activity in other plant parts is derived solely from the roots, and when, and to what degree it is derived by synthesis in situ. 

After the initial imbibition phase and hydration of the cell walls and cell contents the matric potential (i/ J plays a minor role in attracting water into the cell. Indeed, some of the matrices, e.g. protein and carbohydrate storage products in the storage organs, are later hydrolysed to low molecular weight, osmotically-active substrates which decrease (make more negative) the of both the seed as a whole, and, when transported there, of the growing embryonic axis (Chap. 6). The increase in water uptake in Phase III is thus initially asso-... 

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