Question

What is the use of introducing the property of delayed fruit ripening in some plants? Explain the methods used for delaying fruit ripening.

Hint:

The Flavr Savr tomato, developed by Calgene in 1994, was the first genetically modified food approved for human consumption, utilizing antisense technology to delay softening.

Answer 1

Step 1: Advantages of Delayed Fruit Ripening
Introducing delayed ripening has major agricultural and economic benefits:
1. Reduces Post-Harvest Loss: Fruits remain firm for a longer period, preventing soft bruising and spoilage.
2. Extends Shelf-Life: Fruits can be stored for longer periods, allowing them to be shipped long distances or exported without expensive refrigeration.
3. Retains Quality: Fruits retain their flavor, aroma, nutritional value, and texture during transport, ensuring high-quality produce reaches consumers.


Step 2: Methods Used to Delay Ripening
Fruit ripening is controlled by the gaseous plant hormone ethylene. Delayed ripening is achieved by genetically suppressing ethylene synthesis or action:
1. Antisense RNA Technology (e.g., Flavr Savr Tomato):
- Softening occurs when the enzyme polygalacturonase (PG) degrades cell-wall pectin.
- Scientists introduced an antisense gene that produces RNA complementary to the normal PG mRNA.
- These two strands hybridize to form double-stranded RNA, blocking the translation of the PG enzyme and keeping the fruit firm.
2. Suppression of Ethylene Biosynthesis Genes:
- Ethylene is synthesized from S-adenosylmethionine via the precursor 1-aminocyclopropane-1-carboxylic acid (ACC).
- Using antisense genes to silence ACC synthase or ACC oxidase (enzymes in this pathway) reduces ethylene production, delaying ripening.
3. Expression of ACC Deaminase:
- Introducing a bacterial gene (e.g., from Pseudomonas) for ACC deaminase breaks down ACC into ammonia and $\alpha$-ketobutyrate.
- This diverts the precursor away from ethylene synthesis, lowering ethylene levels and delaying ripening.
Final Answer: Delayed ripening reduces post-harvest losses and extends fruit shelf-life during transport. This is achieved using antisense RNA to silence pectin-degrading enzymes (like polygalacturonase) or by suppressing ethylene synthesis (silencing ACC synthase/oxidase, or expressing bacterial ACC deaminase).