The outermost proteinaceous layer of maize endosperm is called

The correct option is aleurone.

Step-by-step Explanation:

1. Understanding Maize Seed Structure: Maize (corn) is a monocotyledonous plant. A maize grain is actually a single-seeded fruit (known as a caryopsis) where the seed coat is fused with the fruit wall (pericarp).

2. The Endosperm: The bulk of the maize seed contains a large, starch-storing tissue called the endosperm, which provides nutrition to the developing embryo during germination.

3. The Aleurone Layer: The endosperm is surrounded by a specialized, single-layered outer boundary called the aleurone layer. This layer is highly proteinaceous and plays a crucial role in secreting hydrolytic enzymes (such as amylases) that break down the stored starch in the endosperm during seed germination.

4. Evaluating Other Options:
- pericarp: This is the fruit wall, which is fused with the seed coat in maize, forming the outermost protective layer of the entire grain, but it is not a part of the endosperm itself.
- epidermis: This refers to the outermost layer of cells covering the plant body, not specifically the endosperm.
- tunica: This is a layer of cells found in the shoot apical meristem, unrelated to seed anatomy.

Therefore, the outermost proteinaceous layer of the maize endosperm is the aleurone layer.