Ultrastructure of the symbionts and mycetocytes of bird cherry aphid (Rhopalosiphum padi)

As is known for other aphids, the symbiont cytoplasm in Rhopalosiphum padi is differentiated into a central eccentric and a cortical region which contains electron-lucent nucleoplasm and DNA fibrils. The cytoplasm is surrounded by a plasma membrane, cell wall and perisymbiotic membrane which are separated by periplasmic spaces. The periplasmic space between the cell wall and perisymbiotic membrane contains small vesicles. The symbionts are packed into mycetocyte cells which contain a large nucleus and all the normal cell organelles. For the first time, however microtubules and microfilaments have been identified, but only at high magnification and evidence has been found which makes it possible to propose a mechanism of vesicular transport.