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Rac­col­ta di imma­gi­ni del seme di mais con diver­si ingrandimenti

Descri­zio­ne pre­sa da https://www.flickr.com/photos/146824358@N03/33762056788/in/album-72157679942049418/

The Bran is the outer­mo­st layer of the seed. It con­sists of a seed coat that is fused with the peri­carp, which is made of seve­ral dif­fe­rent layers. The­se layers are the epi­der­mis, the meso­carp, a sec­tion of cross cells and a sec­tion of tube cells. The­se extra layers and the seed coat make up the Bran.

Past the Bran lies the outer­mo­st layer of the endo­sperm, a sin­gle layer of dar­kly stai­ning cuboi­dal cells kno­wn as the Aleu­ro­ne layer (foto3). The cells of the Aleu­ro­ne layer are rich in pro­tein and lipid inclu­sion bodies. The Aleu­ro­ne layer func­tions in the syn­the­sis of the enzy­me α‑amylase which is secre­ted during ger­mi­na­tion, and moves into the endo­sperm in order to begin brea­king down starch into mal­to­se and glucose.

The endo­sperm is the bulk of the seed. It ser­ves mostly to sto­re starch as a fuel reser­ve for the seed during ger­mi­na­tion, and has been kno­wn to sto­re pro­teins. The Endo­sperm is split bet­ween two types of cells, hor­ny endo­sperm and flou­ry endo­sperm. Hor­ny endo­sperm is more abun­dant near the peri­carp and coty­le­don, and stains pink. Flou­ry endo­sperm sits rou­ghly in the midd­le, and stains blue. Flou­ry endo­sperm cells are gene­ral­ly lar­ger, and the starch gra­nu­les are more like­ly to be sphe­ri­cal and less com­pact, com­pa­red to the hor­ny endo­sperm, which is has poly­go­nal and com­pact gra­nu­les and smal­ler cells. Hor­ny endo­sperm also gene­ral­ly has more gra­nu­les than floury.

The Coty­le­don is the outer­mo­st layer of the embryo­nic sec­tion. An alter­na­ti­ve name for the Coty­le­don is the scu­tel­lum. The Coty­le­don is gene­ral­ly the “fir­st leaf” of the plant, in that it ejec­ts from the ker­nel and gro­ws to the sur­fa­ce. It’s bor­der with the endo­sperm is clear­ly mar­ked by a distinct layer of pali­sa­de like epi­der­mis. The­se elon­ga­ted epi­the­lial cells secre­te hor­mo­nes into the endo­sperm that acti­va­te the enzy­ma­tic dige­stion of star­ches. The­se star­ches are absor­bed by the Coty­le­don and trans­fer­red to the deve­lo­ping embryo. A well-defi­ned vascu­lar strand can be seen for­ming within the paren­chy­ma cells of the cotyledon.

The Embryo, or germ con­sists of the coleop­ti­le, plu­mu­le, radi­cal, hypo­co­tyl, and coleo­rhi­za. The coleop­ti­le begins with the nor­thern­mo­st tip of the embryo, and can be distin­gui­shed by its cuti­cle and pali­sa­de epi­der­mis. It has typi­cal leaf pro­per­ties, like­ly becau­se it func­tions as a pro­tec­ti­ve sheath sur­roun­ding the shoot. Under­neath the coleop­ti­le is the plu­mu­le, or embryo­nic shoot, which is a sec­tion of rapid­ly divi­ding cells. The plu­mu­le bears the true “fir­st lea­ves” of the plant. Below the plu­mu­le is the hypo­co­tyl, which is a con­nec­ting struc­tu­re bet­ween the plu­mu­le and radi­cle. It func­tions by hel­ping to “push” the coty­le­don out of the ground during deve­lo­p­ment, and will even­tual­ly beco­me part of the stem. The radi­cle is the cur­ved struc­tu­re beneath the hypo­co­tyl, and will even­tual­ly turn into the pri­ma­ry roo­ts of the plant. Just beneath the radi­cle are an inner dark stai­ning root cap and outer pink stai­ning coleo­rhi­za that pro­tect the root tip during germination.

Peri­car­po

Peri­car­po del seme di mais a 400 ingrandimenti

Endo­sper­ma a sini­stra ed embrio­ne a destra

Pare­te del pericarpo

 

Bran and Aleu­ro­ne Layer with Hor­ny Endosperm

Cel­lu­le del­l’em­brio­ne nel Cotyledon

ingran­di­men­to

Cel­lu­le del­l’em­brio­ne del mais ingran­di­men­to 400x

Cel­lu­le del­l’em­brio­ne del mais

 

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