The correct option is Kinetin.
Explanation
The discovery of plant growth regulators often resulted from accidental observations during physiological experiments. The identification of cytokinins, a class of hormones that promote cell division (cytokinesis), is directly linked to tissue culture experiments conducted by F. Skoog and his colleagues.
Detailed Analysis:
- Skoog’s Observation: F. Skoog and his co-workers observed that callus (a mass of undifferentiated cells) derived from the internodal segments of tobacco stems proliferated only when the nutrient medium containing auxins was supplemented with specific extracts. These supplements included extracts of vascular tissues, yeast extract, coconut milk, or DNA.
- Isolation of Kinetin: In 1955, Miller et al. successfully isolated and crystallized the active substance responsible for promoting cytokinesis from autoclaved herring sperm DNA. They named this substance Kinetin.
- Chemical Nature: Kinetin is chemically known as N6-furfurylamino purine, a modified form of adenine (a purine base). It does not occur naturally in plants but was the first cytokinin-like substance identified.
Analysis of Incorrect Options:
- Abscission II Abscission II & Dormin Dormin: These substances were independently isolated by different researchers studying abscission and dormancy. They were later found to be chemically identical and named Abscisic Acid (ABA), which functions primarily as a growth inhibitor.
- Zeatin Zeatin: Zeatin is a natural cytokinin isolated from corn kernels (Zea mays) and coconut milk. While it serves a similar function to Kinetin, it was discovered later and is naturally occurring, unlike the Kinetin isolated from herring sperm DNA.
Key Takeaway:
Kinetin was the first cytokinin discovered, isolated from autoclaved herring sperm DNA during Skoog's experiments on tobacco callus proliferation.