Question

Length of the pollen tube depends on the distance between
A. Pollen grain and upper surface of stigma
B. Pollen grain on upper surface of stigma and ovule
C. Pollen grain in anther and upper surface of stigma
D. Upper surface of stigma and lower part of style

Answer 1

A pollen tube is a tubular structure formed when germinating by the male gametophyte of seed plants. In the plant life cycle, pollen tube elongation is an essential step.

Complete Answer:
The pollen tube acts either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly in some gymnosperms through ovule tissue to transfer the male gamete cells from the pollen grain cells. In maize, to traverse the length of the pistil, this single cell can grow longer than 12 inches (30 cm).

For sexual reproduction to occur in seed plants, pollen tube formation is important. Pollen grains are brought to the female gametophyte by wind , water or pollinators. One such transport strategy involves shifting from the stigma into the style. If a pollen grain has been inserted by self-incompatibility mechanisms with a compatible stigma, the germination phase is initiated.

The pollen grain undergoes a conformational shift during this process, whereupon a given segment begins to protrude outward to form a tube-like structure, referred to as the pollen tube. This structure descends rapidly through tip-directed growth down the length of the style, reaching rates of 1 cm/h, while carrying two non-motile sperm cells. The pollen tube ruptures upon meeting the ovule, thereby supplying the sperm cells to the female gametophyte, eventually resulting in a double fertilisation event.

The first fertilisation event produces a diploid zygote, and a triploid endosperm is formed by the second fertilisation event. Separate systems such as microsporocytes and megasporocytes have pollen grains.

The correct Answer is option (B) Pollen grains on the upper surface of stigma and ovule.

Note: Pollen tubes are an exemplary model for understanding the behaviour of plant cells. They are easily grown in vitro and have a very active cytoskeleton that polymerizes at very high rates, offering interesting mechanical properties to the pollen tube. The pollen tube germinates from the pollen grain in angiosperms and grows through the stigma, style, ovary and ovules to meet the eggs over the entire length. Pollen tubes were first discovered in the 19th century by Giovanni Battista Amici.