Study Pollen Tube Growth on Stigma

Our Objective

To study pollen tube growth on stigma

The Theory

 Aflowering plant's life cycle includes pollination. Pollination is the process of transferring pollen grains from a flower's anthers to its stigma or to another flower’s stigma, whether through abiotic or biotic mechanisms. Abiotic refers to the fact that the pollen is not conveyed by living things but rather by forces like wind or water. Animals, insects, and birds can all play a role in biotic pollination. Biotic pollination is the primary method to fertilize most plants.

Pollen Germination
Pollen germination is the first step in the fertilization process. It occurs when a mature pollen grain lands on the stigma of a compatible flower. Before reaching the stigma, pollen grains are produced in the anthers of the flower's male reproductive organ called the stamen.The pollen grain consists of two cells: the vegetative cell and the generative cell. The vegetative cell is responsible for producing the pollen tube, while the generative cell will eventually divide to form two sperm cells.

When a pollen grain lands on a receptive stigma, it absorbs moisture and nutrients from the stigma's surface. This initiates a series of biochemical reactions that activate the pollen grain's metabolism. As a result, the vegetative cell begins to grow, forming a pollen tube. The pollen tube elongates and starts to penetrate the stigma tissue, ultimately reaching the ovary through the style, which is the long tube connecting the stigma to the ovary.

Pollen Tube Growth on Stigma
Once pollen germination occurs on the stigma, the pollen tube growth begins. The pollen tube plays a vital role in delivering the sperm cells from the stigma to the ovule, where the female gametophyte or embryo sac is located.

The pollen tube grows through the tissues of the style by digesting its way through. The process of tube growth is driven by the tip of the pollen tube, which is rich in enzymes and other substances that facilitate cell wall degradation and tissue penetration. Pollen tube growth is an example of tip growth of cellular process.

The pollen tube's growth is guided by various chemical signals and cues from the female reproductive structures, ensuring that it grows towards the ovules. This process is known as chemotropism. Once the pollen tube reaches the ovule, it enters through a small pore called the micropyle and releases the two sperm cells. One of these sperm cells fuses with the egg cell, forming a zygote (fertilized egg), while the other sperm cell combines with two polar nuclei in the central cell to form the triploid endosperm, which provides nutrients to the developing embryo.


Learning Outcomes

  • Students understand the term pollination.
  • Students can learn on how germination take place in plants.
  • Students understand the concept of pollen tube growth on stigma.