Page 4 - Scialabba_alii_1999
P. 4
The mucilaginous celis often had a minute protuber- KD. Protein conteni was high in ha rd green-brown
ance similar to a column (Fig. 6) on the inner tan- seed (Fig. 12b) and ripe brown seeds (Fig. 12c),
gential wall protruding into the celi lumen. This with no evidence of qualitative differences.
structure is probably a residual of the protoplast in
the basai portion of the celi. Subepidem1al parenchy- DISCUSSION
ma celis became crushed. The inner layer of the out-
er integument was the tìrst to differentiate, becoming The morphological and histochemical changes of
the palisade layer with thickenings on the radiai and developing seeds of Bra.uica 11WcrocwJW werc
tangential walls. The outer layer of the inner integu- foliowed from the early stages after anthe.,i-. up to
ment died and was compressed Lo form the pigment- maturity. Using embrym of different age~. an
ed layer. The endosperm was reduced to two layers: attempt was made to relate developmental stages
the one-layered aleurone and the hyaline com- of the embryo Lo changes in esterase and phos-
pressed layer. Esterases and acid phosphatases were phatase activity and in the presence/absence of
detected in the column (Fig. 6), the radiai and inner phenols. The development of the embryo preced-
tangential walls of mucilaginous celis (Fig. 7), the ed that of the seed integuments. During secd
aleurone and hyaline layers and in the procambial development mosl celi layers of the ovule integu-
and parenchyma celis of the embryo (Fig. 8). Phe- ments disappeared. the cytoplasm was reabsorbed
nols were detected in the radiai and extemal periph- and the walis became crushed. The structure of
eral walb of mucilaginous celb (Fig. 9). ripe seeds was similar to that described for Cru-
The mature seed, not strictly spherical, \\a~ ciferae b) Yaughan et al. ( 1971 ). ln B. macm-
almost 2-3 mm long, brownish with grey stripes carpa, esterases. acid phosphatases and phenoll.
and with two integuments and a yeliowish or increased during development. but decreased in
sometimes green embryo. The oily cotyledons ripe seeds. suggesting ù1at they play a temporary
folded along the mid axis Lo fonn a duct. The functional role. Phenols were found in celis where
external integument consisted of a mucilaginous esterasc activity had previously been detected.
layer. a crushed subepidermal parenchyma layer Generai esterases are related to the lysosomal
and a palisade layer. The inner integument consist- function of the vacuoles (Mc Lean and Gahan,
ed of a crushed pigmented epidermal layer. This 1969a) or they may occur in the cytoplasm where
was followed by an aleurone layer and a hyaline they are synthesized and transported to the celi
layer (Fig. l 0). The embryo, the walis of the walis in construction (Mc Lean and Gahan,
mucilagino us cells, the aleurone and the hyaline 1969b) . In B. napus seeds, 80% of ali phenols are
layers were positive for esterases. Phosphatase esterified phenolic acids (Naczk and Shahidi,
acti vity was strong in the column of the mucilagi- 1992). besides the esterases hydrolyse aliphatic
nous celis and low in the subepidermal and hyaline and aromatic esters (Gahan, 1984); therefore we
layers of the integumcnts. In the embryo, the walis suppose that in B. macrocwpa the esterases may
of the parenchymatous cells, which define the also be involved in the hydrolysis of phenolic
interceliular spaces of the cortical cylinder (Fig. esters leading Lo the formation of phenolic acids.
Il ) and the adhesion regions of the cotyledons Phenols have an antimitotic effect (Podbielkows-
were positive for phosphatase activity. ka et al., 1994). and, therefore. could be a defense
Starch was absent in ripe sccds, but carbohy- system against infections during seed maLUration
drates were localized on the walis of the hyaline or seed germination. or they could prevent germi-
and aleurone layers (not shown). Lipid reserves nation by blocking mitosis.
were abundant in the embryo, and lipid droplets Duri ng seed development of B. macrocarpa, we
were detected in the cells of the aleurone and pig- observed a reduction in starch content, the appear-
mented layers. Phenols were scanty in mucilagi- ance of polysaccharides in mucilaginous celis and
nous celis, the palisade layer, root tip, and abun- the pigmented layer, together with an increase in
dant in the pigmented layer. proteins and lipids. Starch was present in the first
Protein content changed during maturation: green stage of development. was absent in ripe seeds and
seeds (Fig. 12a) were characterized by low protein its digestion was associated with mucilage deposi-
content with molecu lar weight of 2 1, 22, 27 and 30
ISO
