Phalloidin is a peptide that can be conjugated to fluorescent dyes, such as fluorescein, and used to label actin in cells. Phalloidin-fluorescein was added to dividing, ciliated cells in culture. Where will the fluorescence be localized in the cells when looking at the treated cultures using fluorescence microscopy?
a. at the inner surface of the inner nuclear membrane
b. at the inner surface of the plasma membrane
c. microtubule-organizing centers (MTOC) cilia
d. more than one of the above.

b. at the inner surface of the plasma membrane

Explanation:

Phalloidin is a type of toxic substance that is found in dead cap mushrooms. It has a bicyclic structure of heptapeptide. It has a great ability to bind with the filamentous actin selectively and tightly. So it is used in the fluorescent microscopic study to detect or identify the structure or position of the F- actin. Due to phalloidin small structure, generally it is used in the labeling of cellular protein during the fluorescent microscopy to increases high resolutions. Since most of the actin is connected with the inner surface of the plasma membrane so the cells that are treated with phalloidin, has fluorescence at the inner surface of the plasma membrane.