Post Harvest Technology, Ripening and senescence of fruits and vegetables .

Ripening and senescence of fruits and vegetables

1. An Assignment on ETHYLENE BIOSYNTHESIS, PERCEPTION AND MOLECULAR MECHANISM OF ACTION; REGULATORY ROLE OF ETHYLENE IN SENESCENCE AND RIPENING COURSE TITLE- RIPENING AND SENESCENCE OF FRUITS AND VEGETABLES COURSE NO.- PHM- 601 CREDIT HOURS- 2 (1+1) Submitted to Er. Bhagwat Kumar Krantikari Debridhur College of Horticulture and Research Station, Jagdalpur Submitted by Vidhya Sagar Mali Ph.D previous year Dept. of Fruit Science Mahatma Gandhi University of Horticulture and Forestry (C.G.)

2. Contents Introduction Occurrence, distribution and transport Site of synthesis Structure and biosynthesis Molecular mechanism of action Regulatory role of ethylene Conclusion Mahatma Gandhi University of Horticulture and Forestry (C.G.) References

3. Mahatma Gandhi University of Horticulture and Forestry (C.G.) 1 Introduction Ethylene is a natural plant hormone released by all plant tissues and microorganisms. It is also called as ‘Ripening hormone’, as it plays an important role in fruit ripening process. Low concentration of 0.1-1.0 microlitres is sufficient to trigger the ripening process in climacteric fruits. It has autocatalytic activity because of which such small quantities can trigger further release of large quantities of ethylene by the fruit tissues. Very little response is only seen to exogenous application of ethylene in case of non-climacteric fruits. .

4. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Occurrence and distribution 2 Ethylene can easily be synthesized in all plant organs such as roots, stems, leaves, tubers, fruits and seeds . It is highest in senescing tissues and ripening fruits . Within the plant organs, ethylene formation is mainly located in peripheral tissues. Ethylene is biologically active at low concentration (less than 1 ppm). Ethylene can easily pass through plasma membrane into the cell , easily diffuse within the plant, and flushed out of plant tissues through intercellular spaces. Transport In comparison to ACC synthesis and ACC oxide, less is known about ethylene perception and single transduction , because of difficulties in isolation and purifying ethylene. ( Transport by diffusion )

5. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Site of synthesis It is naturally produced in plants & synthesized from any part of the plant. The production of ethylene in accelerated at the time of ripening of fruits, leaf fall, senescing flowers, injuries, drought stress etc. Maturing fruits, meristematic region, nodal region are the sites of actively synthesis. Synthesis Ethylene get synthesized naturally in mature fruits, aging leaves etc. Physiological stress like- wounding, bruising, flooding, chilling, temperature, cutting etc. 3

6. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Structure and biosynthesis Ethylene is the simplest olefin (mol. w t. 28 ). Chief precursor of ethylene is the containing amino acid methionine. 4

7. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Biosynthesis of Ethylene Pathway of ethylene synthesis is given by Yang 1980. The amino acid methionine is precursor of ethylene and ACC (1-aminocyclopropane – 1 carboxylic acid) serves as an intermediate between methionine and ethylene. When methionine is conjugated with adenosine gives rise to SAM (S- adenosyl methionine) in presence of enzyme adomate synthetas and it used a molecule of ATP. SAM in presence of aminocyclopropane carboxylic acid synthetas (ACC synthetas) break down into aminocyclopropane carboxylic acid and S- methylthioadenosine. Aminocyclopropane finally converted into ethylene in presence of ACC oxidase. This reaction is presumed to be triggered by ethylene forming enzyme (EFE). 5

8. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Molecular mechanism of ethylene action 1.Membrane permeability Ethylene acts by changing permeability of the cell membrane. Ethylene is lipid soluble, hence it gets dissolved in lipid membrane and alters the permeability of membrane. 2.Nucleic acid and protein metabolism Some response like fruit ripening & abscission are due to the gene expression and protein synthesis. Synthesis specific mRNA and enzymes. Reduce biosynthesis of auxins and inhibits its transport. 3.Regulation of auxin metabolism 6

9. 7 Mahatma Gandhi University of Horticulture and Forestry (C.G.) Contd… - Increased permeability increases RNA and protein synthesis . - It also accelerates the secretion of variety of enzymes like polygalactourinase, cellulose and phospholipase they softening and degradation of cell wall. - ᾳ -amylase enzymes it results in hydrolysis of starch into sugars . - High permeability increases respiration thereby hastens fruit ripening process.

10. 8 Mahatma Gandhi University of Horticulture and Forestry (C.G.) Mode of action Ethylene, acts in symphony with other plant hormones (auxins, gibberellins, kinins and abscissic acid) to exercise control over the fruit ripening process. The relationship of other plant hormones to ripening is as yet not clearly defined. Different fruits do have different level of ethylene production. Climacteric and non-climacteric fruit appear to differ in in control of ethylene synthesis. The biosynthesis of ethylene in climacteric fruit is said to be autocatalytic. Climacteric fruits exposed to propylene begin to synthesize ethylene in an autocatalytic manner; non-climacteric fruit show no such response.

11. Mahatma Gandhi University of Horticulture and Forestry (C.G.) 9 R egulatory role of ethylene in senescence and ripening Changes occur during ripening Structural changes Physical changes Biochemical changes The fruit will become less firm as the structure of the fruit is degraded. When a substance undergoes a change that does not change its chemical composition. The chemical composition of fruits changes and it is irreversible.

12. 10 Mahatma Gandhi University of Horticulture and Forestry (C.G.) 1. Structural changes Cell wall- Cellulose fiber starts breaking and middle lamella dissolves which leads to softening of fruit. Cell membrane- Becomes permeable. Intercellular space- Porosity reduced. Chloroplast- Change into chromoplast. Cuticle- Deposits of cuticles and wax e.g. grape and pear. Epidermal hair- Number reduced or disappeared e.g. Rambutan Lenticels and stomata- Number increased as a result fruit shriveled, shorter storage life. Sclerenhyma and vascular bundle- Become lignified.

13. 11 2 . Physical changes Color- Loss of chlorophyll which is accompanied by synthesis of anthocyanin, carotenoid, xanthophylls giving the fruits characteristics colour. Water content- Decline in water content persisted throughout the ripening process in some fruit, whereas in other it reversed during the progression of the ripening e.g. Potato. Dry matter- As the fruit matures it accumulates a lot of starch and some sugar. As the fruit ripens starch is converted to sugar. Thus the DM of fruit at harvest is a good indicator of the sugar content of the fruit when fully ripe. Fruit firmness- Decreased during ripening. Specific gravity- The specific gravity increases within expected of fruit weight and fruit volume at ripening stage. Fruit shape – The shape of fruit can change during maturation and can be used as a indication to determine harvesting. Mahatma Gandhi University of Horticulture and Forestry (C.G.)

14. 3. Biochemical changes 12 Hormonal changes- Ethylene Change in pigments Increase in activity of enzymes Change in pectin substances Change in phenols Synthesis in volatile compounds Change in acids Change in carbohydrates Mahatma Gandhi University of Horticulture and Forestry (C.G.)

15. Conclusion 13 Mahatma Gandhi University of Horticulture and Forestry (C.G.) 1. Ripening , itself considered to be readiness for harvest, brings about many specialized changes the in fruit that makes it aesthetically appealing. These changes are essentially genetically controlled and much less can be done to alter them at the eye level. 2. Ethylene plays an important role in governing the ripening cycle. The study of changes related to ripening helps in differentiation between desirable and undesirable changes occurring due to ripening. 3. Biotechnological alterations can help in manipulation of the ripening process for the benefit of human kind. Control of ripening process can render the produce to be more aesthetically sound for longer duration and delaying the senescence and undesirable changes.

16. Mahatma Gandhi University of Horticulture and Forestry (C.G.) References