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The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae (in the RER), and tubular structures in the SER. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum is not found in red blood cells, or spermatozoa.
The outer nuclear membrane also shares a common border with the endoplasmic reticulum. [8] While it is physically linked, the outer nuclear membrane contains proteins found in far higher concentrations than the endoplasmic reticulum. [9]
The endoplasmic reticulum (ER) is a synthesis and transport organelle that branches into the cytoplasm in plant and animal cells. [3] The Golgi apparatus is a series of multiple compartments where molecules are packaged for delivery to other cell components or for secretion from the cell. [ 4 ]
The desmotubule (DM) is shown as a continuation of the endoplasmic reticulum (ER), with various membrane proteins linking it to the plasma membrane (PM). A desmotubule is an endomembrane derived structure of the plasmodesmata that connects the endoplasmic reticulum of two adjacent plant cells.
Unlike animal cells, almost every plant cell is surrounded by a polysaccharide cell wall. Neighbouring plant cells are therefore separated by a pair of cell walls and the intervening middle lamella, forming an extracellular domain known as the apoplast. Although cell walls are permeable to small soluble proteins and other solutes, plasmodesmata ...
Smooth endoplasmic reticulum makes hormones and lipids, degrades toxins, and controls cellular levels of calcium. Though most control of cell division is present in the nucleus, the centrosomes present in the endoplasm assist with spindle formation. The endoplasm is the site of many activities necessary for the cell to maintain homeostasis. [2]
Plant cells lack centrioles or spindle pole bodies except in their flagellate male gametes, and they are entirely absent in the conifers and flowering plants. [4] Instead, the nuclear envelope itself appears to function as the main MTOC for microtubule nucleation and spindle organization during plant cell mitosis.
One of the few organelles they do contain at maturity is the rough endoplasmic reticulum, which can be found at the plasma membrane, often nearby the plasmodesmata that connect them to their companion or albuminous cells. All sieve cells have groups of pores at their ends that grow from modified and enlarged plasmodesmata, called sieve areas.