Question

In Pinus, endosperm cells have 30 chromosomes then how many chromosomes are present in sieve cells?

Answer 1

Pinus are trees or shrubs belonging to the pine family. It includes various commercially important trees such as cedars, firs, hemlocks, larches, pines and spruces. It is included in the order Pinales. The Pinus trees are evergreen, coniferous resinous trees.

Complete answer:
Pinus are gymnosperm as they bear naked seeds without any seed coat and are non-flowering in nature. In Pinus, the endosperm is not a true endosperm and sieve cells are cells that are associated with the functioning of the phloem.

Endosperm is produced as a tissue inside the seeds of most flowering plants and gymnosperms. It surrounds the growing embryo. It helps in the nutrition of the developing embryo in the form of starch, oils and protein. In gymnosperms, endosperm is not true endosperm. Endosperm in gymnosperm does not arise due to double fertilization. Between the two sperm nuclei, one of them degenerates as a result, endosperm is not a real endosperm. However, a nutrition providing tissue is essential for the embryo to grow and germinate.

Sieve cells are specialized cells that are important for the function of phloem. The sieve cells form the part of the phloem which is a highly organized tissue and functions in the transportation of organic compounds made during photosynthesis. The sieve cells in the gymnosperms do not contain companion cells. The sieve cells in gymnosperms are diploid or 2n.

In Pinus, endosperm is formed before the process of fertilization. It is the result of pre-fertilization tissues. As it is formed without fertilization, endosperm is haploid. It is the same as that of the female gametophyte and so it is haploid and contains a number of chromosomes. Hence, if the endosperm in Pinus is haploid(n) with 30 chromosomes, the sieve cells will have 60 chromosomes as it is diploid or 2n.

Note: Pinus is a gymnosperm. In Pinus, endosperm arises before fertilization and hence it is haploid. Whereas, sieve cells are the specialized transport cells of the phloem system and are diploid. Therefore, sieve cells of Pinus will have 60 chromosomes as it is diploid, 2n and endosperm is haploid with 30 chromosomes.