Growth and Development of Horticultural Crops (1+1)

3. Hormonal control of ripening

• Ethylene has been established as a ripening hormone. Massive doses of ethylene can bring about ripening changes in immature fruits. So, it is the hormone which plays the most powerful regulatory role in ripening. It has been observed that a rise of ethylene level occurs at the onset of the climacteric rise and can be assigned the role of the trigger of ripening.
  
• They proposed that the onset of ripening is associated not only with a rise in the ability to biosynthesize ethylene but also a marked increase in ethylene responsiveness. It has also been found that ethylene can induce a respiratory climacteric in some leaves and develop many of the pigments commonly developed in fruit ripening. In general, ethylene may be bringing about the formation of new types of enzymes in fruits.
  
• However, ethylene is not a universal ripening hormone. Some climacteric fruits like strawberry and citrus have no effect on their ripening by the ethylene treatment.
  
• Leopold and Kriedemann (1975) concluded that ripening appears as an unveiling enzyme system which brings about the alteration of the fruit, and respiratory energy must be provided both for the synthesis of the new enzymes system and for their actions in ripening. Hormonal regulation may be involved in the change from a mature fruit resistant to a ripening to one which becomes receptive to ripening signals.