Angiosperm Sieve Elements: Key Features

Sieve elements are the conducting cells of the phloem tissue in plants, responsible for transporting sugars. In angiosperms, these mature cells undergo significant structural changes to optimize transport efficiency.

Components of Mature Sieve Elements

Let's examine the given options in the context of mature sieve elements in angiosperms:

• P-proteins: These proteinaceous filaments are present in the cytoplasm of mature sieve elements in angiosperms and play a role in sealing off damaged sieve tubes.
• Callose: This polysaccharide is often deposited around sieve areas and on sieve plates, especially during dormancy or after injury, but it is fundamentally associated with sieve areas.
• Sieve plate: This is a defining feature of sieve elements, characterized by pores that connect adjacent sieve tube members, facilitating longitudinal flow. It is present in mature cells.
• Nucleus: Mature sieve elements in angiosperms are highly specialized and characteristically lack a nucleus. This anucleate state, along with the absence of a vacuole and other major organelles, maximizes the lumen space for phloem sap flow.

Conclusion on Absence

The most notable absence in a mature sieve element of an angiosperm, crucial for its function, is the nucleus. This allows for unimpeded longitudinal transport of photosynthates through the sieve tube.