The metal constituent of chlorophyll is

Chlorophyll is the primary pigment responsible for light absorption during photosynthesis in plants. The chemical structure of chlorophyll consists of a porphyrin-like macrocycle called a chlorin ring, which is composed of carbon, nitrogen, and hydrogen [t2][t4]. At the absolute center of this ring structure, a magnesium ion (Mg2+) is sequestered [t1][t4]. This central magnesium atom is essential for stabilizing the molecule and facilitating the transfer of electrons down the electron transport chain to drive energy production [t4][t5]. While other metals like iron or manganese are involved in different stages of plant metabolism or the oxygen-evolving complex, magnesium is the specific metal constituent that occurs within the chlorophyll molecule itself [c1][t7]. Without magnesium, the chlorophyll molecule cannot function effectively to harvest light energy [t5].

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Nitrogen (N) > p. 363
2. [2] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/chlorin
3. [3] https://www.arsdcollege.ac.in/wp-content/uploads/2020/03/Role-of-Mg.pdf