Question

What is the function of p-protein and callose protein in the conduction of food from the phloem?

Answer 1

Conduction of food materials is the key feature of the phloem. So here, P-protein and callose protein act as a defense for defence, in fact, we can actually call them a damage control team.

Complete step by step answer: P-proteins are phloem proteins and their function is not yet fully known. They appear to play the "damage control" if the phloem is hurt. Upon failure of the sieve element, the P-proteins quickly aggregate into the sieve plate to form a clot that avoids the leakage of the phloem from exuding through the wound. PP1 and PP2, pumpkin phloem proteins, are examples of P-proteins that tend to be synthesised in CC and transported to SE. PP2 is not present at the early stages of development but starts to be generated by the CC and transported to the SE later in development.
Callose, Beta-1-3-Glucan, is a carbohydrate that is often stored in the sieve plate in reaction to injury. However, there is some question as to whether the callose is immediately deposited in response to the injury or whether it is a secondary response to the manipulation needed for a microscopic view of the sieve element. Callose accumulation often occurs in old, non-functional sieve elements and is likely to close the old elements to keep the phloem translocation stream working.

Note: The existence of Callose in sieve plates has been recognised for a long time, but the way this polysaccharide plug is synthesised has remained unexplained. Two independent laboratories have recently documented the detection of Callose synthase 7 also known as CalS7, also known as glucan synthase-like 7 GSL7, as the enzyme accountable for Callose accumulation in the sieve plate.