Following statements were made with respect to plant steroid hormones:

A. The receptors for plant steroid hormones are found in the nucleus, similar to animal steroid hormones.
B. There are multiple pathways for the plant steroid hormone biosynthesis involving the cytochrome P450 class of enzymes.
C. The first plant steroid hormone was isolated from male gametophytes.
D. Plants deficient for the steroid hormone brassinosteroid show underproliferation of phloem and overproliferation of xylem cells.
E. Castasterone is a plant steroid hormone abundant in the vegetative tissues of the plant.

Which one of the following options represents the combination of all correct statements?

Correct option is B

Statement A: "The receptors for plant steroid hormones are found in the nucleus, similar to animal steroid hormones." (Incorrect)

• In plants, the receptors for brassinosteroids are typically located in the plasma membrane, not in the nucleus, unlike animal steroid hormones, where receptors are often in the cytoplasm or nucleus.
  

Statement B: "There are multiple pathways for the plant steroid hormone biosynthesis involving cytochrome P450 class of enzymes." (Correct)

• Cytochrome P450 enzymes are indeed crucial in the biosynthesis of brassinosteroids and other plant steroids. These enzymes catalyze essential steps in steroid hormone synthesis.
  

Statement C: "The first plant steroid hormone was isolated from male gametophytes." (Correct)

• The first plant steroid hormone, brassinolide, was indeed isolated from rape pollen (a male gametophyte), which later led to the identification of brassinosteroids as a class of plant hormones.
  

Statement D: "Plants deficient for the steroid hormone brassinosteroid show underproliferation of phloem and overproliferation of xylem cells." (Incorrect)

• This statement is not entirely accurate because although brassinosteroid deficiency leads to vascular abnormalities, it’s more specific in causing defective vascular differentiation rather than generalized overproliferation of xylem. It’s a misleading simplification of the physiological effects.
  

Statement E: "Castasterone is a plant steroid hormone abundant in the vegetative tissues of the plant."  (Correct)

• Castasterone is a brassinosteroid, one of the most biologically active steroid hormones, and it is found abundantly in the vegetative tissues of plants.
  

Information Booster :

1. Brassinosteroids (BRs) are essential plant hormones involved in growth, stress tolerance, and reproduction. They regulate cell elongation, vascular differentiation, and flowering.

2. Biosynthesis: BRs are synthesized via cytochrome P450 enzymes, with key intermediates like castasterone and brassinolide.

3. Receptors & Signaling: BRs bind to BRI1 receptors on the plasma membrane, activating signaling pathways that promote cell growth and development.

4. Deficiency Effects: BR-deficient plants show stunted growth, impaired vascular differentiation, and reduced fertility.

5. Castasterone is an active brassinosteroid abundant in vegetative tissues, important for growth and vascular tissue formation.