The wheat grain has an embryo with one large, shield-shaped cotyledon known as

1. Coleoptile
2. Epiblast
3. Coleorrhiza
4. Scutellum

The wheat grain has an embryo with one large, shield-shaped cotyledon known as scutellam. Scutellam is factor of the arrangement of a barley, wheat and rice seed, hence it represent the structure for monocotyledon plants. It is considered as the modified seed leaf and are connected with the embryo sac with the help of vascular tissue. It is a very delicate part with large surface area. It shows considerable performance in absorption of 2,4-D (Dichlorophenoxyacetic acid) on seed germination. When the seeds starts to germinate, the embryo initiates to secrete gibberellic acid (GA). After 24 hours of this process now scutellam starts to synthesize GA. Embryo's scutellum helps in the synthesis and secretion of gibberellin to the aleurone layer of the endospermic seed, as a result, various enzymes are developed. These enzymes permit the compilation of embryo and the products are engrossed by scutellum and moved to the developing embryo.

So, the correct answer is option D.