Question

Rarely in angiosperms, the pollen tube develops further in the embryo sac. The abnormality is called as-
A. Metaxenia
B. Nemec phenomenon
C. Xenia
D. Mesogamy

Answer 1

Hint: In most flowering plants, the megaspore's nucleus undergoes mitosis three times, producing eight haploid nuclei. These eight nuclei make up the female gametophyte.

Complete answer: To answer this question, first we need to know about pollination in plants. The transfer of pollen grains from the anther to the stigma of a pistil is termed pollination. After pollination, the pollen grain germinates and the tube cell begins to form the pollen tube. Usually, the pollen tube enters the embryo sac through the micropyle or opening in the ovule's integuments. There, the sperm discharges into the embryo sac.

Now, let us find the solution from the given options.
Metaxenia is the influence pollen has on the form of fruit and other characteristics of the fruit. Metaxenia can help to classify the best parents of pollenizers to minimize the time of fruit growth and increase yield in mixed cultivar plantings.
Generally, pollen grains have two nuclei. Sometimes, the number of nuclei in some abnormal pollen grains can increase. In 1898 Nemec noticed that the pollen grains in the petaloid anthers of Hyacinthus Orientalis often form large eight-nucleate structures, resembling embryo sacs. He presumed that they resulted from a disintegration of the generative nucleus and three divisions of the pollen's vegetative nucleus.
Xenia is the effect of male parent genes on fruit and/or seed growth. One of the most common examples of xenia is the different colours that can be created by individual pollen grains in maize by an assortment of alleles. These cobs of corn are grown for decorative purposes.
Mesogamy is a form of fertilization where the tube of pollen reaches the ovule through its middle part or through the ovule integuments.

So, the correct answer is option B i.e., Nemec Phenomenon.

Note: There are two haploid nuclei, a tube nucleus and generative nucleus inside each pollen grain. The tube nucleus is involved in the growth of the nucleus down the pistil to the ovary. The generative nucleus produces two sperm nuclei by mitosis. The sperm nuclei move to the ovary through the micropyle. One sperm fuses with the egg forming the zygote, while the other sperm and the polar nuclei fuse to form a triploid cell.