Regulation of Senescence

Senescence is a part of a developmental sequence of events and has to be a controlled process. You must have seen that if you cut twigs having leaves and flowers and put them in flower vases, these twigs senesce faster than if the twigs were still on the parent plant. It has been found that senescence is controlled by both external and internal factors. Of the external factors, plant hormones, length of the day, temperature and nutrient supply play an important role. Of the internal factors, size and age of the plant, degree of flowering and time of ripeness of fruits determine the onset of senescence. In one experiment where the normal time of senescence was 120 days, when mature fruits were removed from plants the time of senescence was delayed.

It occurred after 140 days. And when young fruits and-flowers were removed from plants as soon as they were formed, the senescence was delayed to 160 to 180 days. This means that the senescence is initiated as soon as the process of reproduction is set in. This is probably because a plant needs a lot of nutrition for the growth of flowers and fruits. So to increase the supply to fruits, the stored material from leaves and other parts is translocated to the growing fruits. The demand is so high that the fresh supply of nutrient and photosynthates cannot be replenished. It is a simple case of more demand than supply. Naturally, the system collapses. However, in the process like majority of other organisms the plant tries to ensure that the fruits mature and seeds are set so that it can continue with its progeny. It is a case of self-sacrifice by the parent plant in order to see its seeds develop properly and grow.