Question

Tyloses are seen in__________.
a. Collenchyma
b. Phloem cells
c. Ray parenchyma
d. Ray parenchyma and xylem cells

Answer 1

Permanent tissues are made up of cells that have lost the power to divide and can be simple and complex permanent types. Simple permanent tissues include parenchyma, collenchyma and sclerenchyma and complex permanent tissues include xylem and phloem. Tyloses are the balloon-like large structure found in heartwood.

Complete answer:

As we have learnt that permanent tissues can be simple and complex. Simple permanent tissues are parenchyma, collenchyma and sclerenchyma and complex permanent tissues are xylem and phloem.

We should talk about Xylem first which is the transporter of water from roots to stems and leaves in the plants whereas phloem helps in transporting food. Xylem is interconnected with vessels and tracheids to perform this function. Vessels are long and cylindrical tubes which are devoid of protoplast and tracheids are elongated dead cells with hard lignified wall and wide lumen. Xylem parenchyma are the only living cells in xylem and stores food and water. It is divided into axial parenchyma cells and ray parenchyma cells which radiate out of the common centre.

Now let us talk about Tyloses that are balloon-like outgrowths of protoplast of parenchymatous cells that protrude into the xylem vessels via pits. These outgrowths are formed under stress conditions or when pathogens invade the xylem tissues. Both the axial and ray parenchyma cells adjacent to vessels form the tyloses outgrowths and these parenchyma cells are called contact cells.

It is also interesting to know that nucleus and cytoplasm of these cells migrate into the tyloses and they may differentiate into sclereids.

Hence, the correct answer is option (D).

Note: Some important points to remember:
- Plant families that are devoid of vessels are Winteraceae, Tetracentraceae and Trochondendraceae.
- Some species of Selaginella and Pteridium and order Gnetales of Gymnosperms possess vessels and these are non-angiosperm plants.
- Sieve tubes of phloem are called the RBCs of the plant body as they are devoid of nucleus.