MCQ IN MEDICINE

Detailed explanation-1: -Increased callose deposition at plasmodesmata leads to plasmodesmata closure, which helps restrict pathogen spread. Increased callose deposition in the vascular tissues such as phloem sieve tubes could also functions as a defense mechanism for reducing the colonization and transport of vascular pathogens.

Detailed explanation-2: -Callose is a cell wall material that can be deposited around sieve pores. The deposition leads to as decrease in pore diameter and eventually to coplete occlusion. Callose formation has been shown to occur within minutes after injury and leads to tube occlusion within 10-20 minutes in some species.

Detailed explanation-3: -Callose blocks sieve tubes in winter which is the end of the growing season. Sieve tubes are long, tube-like structures that are one of the types of cells that make up the phloem (food conducting vessel).

Detailed explanation-4: -Callose is involved at multiple stages of pollen development as a structural component. It is also deposited at cell plates during cytokinesis. In addition, callose can be deposited at plasmodesmata (PD) to regulate the cell-to-cell movement of molecules by controlling the size exclusion limit (SEL) of PD.