Aleurone (from Greek aleuron , flour) is a protein found in protein granules maturing from seeds and tubers . The term also describes one of the two main cell types in the endosperm , the aleurone layer . The aleurone layer is the outermost layer of the endosperm, followed by the inner starchy endosperm. This layer of cells is sometimes referred to as the peripheral endosperm. It is located between the pericarp and the hyaline layer of the endosperm. Unlike starchy endosperm cells, aleurone cells remain alive at maturity.
Content
- Analeurone protein
- 2aleurone tissue
- 3aleurone development
- 4aleurone function
- 5References
- 6External links
aleurone protein
Allele proteins can have two different morphological characteristics, homogeneous and heterogeneous. The homogeneous aleurone consists of similar protein bodies (for example, Phaseolus vulgaris ), while the heterogeneous aleurone consists of granules of different shapes and types of proteins covered with a membrane (for example, Ricinus communis ).
multicolored corn has some of its pigments in the aleurone layer.
The aleurone layer surrounds the endosperm of grass seed tissues and is morphologically and biochemically distinct. Starchy endosperm cells are large, irregularly shaped cells and contain starch grains, while aleurone cells are cuboid in shape and contain aleurone grains. In more cultivated cereals ( species of wheat , rye , oats , rice and corn ) the aleurone is a single layer, while barley has a layer of multicellular aleurone. Primary thick cell walls encase and protect aleurone cells.
The aleurone layer is important for both the developing seed and the mature plant. The aleurone tissue accumulates large amounts of oils and lipids that are useful during seed development. It is also a place for mineral storage and in some species, functions in seed dormancy. The aleurone may also express several pathogen-protective proteins, including PR-4. Aleurone also serves as the most dietarily beneficial fraction in many brans. In addition, the aleurone tissue contains many protein-storage vacuoles known as protein bodies. In starchy endosperm cereals, the aleurone contains about 30% of the kernel proteins. In colored corn, anthocyanin pigments in the aleurone layer give the grains a dark bluish-black color.
aleurone development
The development of the aleurone layer involves several periclinal , and anticlinal cell divisions and several steps of genetic regulation. The dek1 gene and crinkly4 (CR4) kinase both function and regulate positive aleurone’s cellular destiny. The normal dek1 gene is required in order to receive and respond to the position signals that determine the fate of the aleurone cells during development.
Mutants of the dek1 gene block, the formation of aleurone and cause cells to develop endosperm cells like starch, instead of aleurone cells. This causes the seed to lack an aleurone layer. This mutation is caused by the insertion of a Mu transpos in the dek1 gene, causing it to malfunction. However, this transposon can sometimes withdraw from the gene, restoring the function of dek1 . Experiences in this area have helped to demonstrate that the signals that determine aleurone positioning are still present in the later stages of development, and the aleurone cells still respond to those signals.
Similar to the dek1 mutation, genes with a mutation in the CR4 gene also cause a switch in the fate of aleurone cells. The CR4 gene codes for a receptor kinase and is therefore involved in signal transduction pathways that involve the fate of aleurone cells. Plants with a mutated CR4 gene are shorter than normal and produce wrinkled leaves.
In addition, several hormones influence the development of the aleurone layer, including auxin , cytokinin , abscisic acid (ABA), and gibberellin (GA). Aids and cytokinin play a role in the early stages of aleurone development. Aleurone maturation is promoted by ABA while germination is promoted by GA.
aleurone function
The aleurone layer performs a variety of functions to help maintain good seed development. An example of this is the maintenance of a low pH in the apoplast . In relation to cereals, the aleurone layer releases organic and phosphoric acids, in order to maintain the pH of the endosperm between a pH of 3.5 and 4. In barley, the aleurone layer also releases nitrite to the starch and apoplast endosperm under anaerobic conditions. In addition, although the function is not clear, a certain class of hemoglobins (Hb) is present in the outer layer of living cells, including the barley aleurone tissue and rice seeds.
During seed germination , the embryo plant produces the gibberellin hormone that triggers aleurone cells to release α-amylase for the hydrolysis of starch, proteases, and storage proteins for the endosperm . Proof that G-proteins play a role in gibberellin signaling events has been obtained. The breakdown of starch supplies endosperm sugars to boost root growth and acrospire . This version of amylase is considered the most important and unique function of the aleurone layer. This effect is inhibited by the vegetable hormone abscisic acid, which keeps the seed dormant. After completing this function, the aleurone cells in the developing seed undergo apoptosis .
Experiments carried out in the 1960s confirmed that in order for the aleurone layer to secrete enzymes that degrade starch, the embryo has to be present. Following removal of the embryo, starch degrading enzymes were not released and no degradation of the starch tissue occurred.
The effect of gibberellin on the aleurone is used in brewing , especially in the production of barley malt where treatment ensures that a batch of barley seeds germinate evenly.
