Factors afftecting growth of pollen grains

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TITLE: FACTORS AFFECTING GROWTH OF POLLEN GRAINS

OBJECTIVE:

To investigate the effects of different concentrations of sucrose solutions and different concentration of boric acid in the growth of pollen grains.

INTRODUCTION:

Pollen grains are produced in the pollen sacs of the anther. Each microspore mother cell undergoes meiosis to produce four haploid cells, each of which produces a pollen grain or a microspore. The haploid nucleus of a pollen grain divides by mitosis to produce two haploid cells which function as male gametes. The pollen grain secretes a thin inner wall, the intine, and a thick outer wall, the exine. The mature pollen grains, containing the male nuclei, are released when the anther wall dries out and the anther splits.

On landing the stigma, the pollen grain absorbs water. The growth of pollen tube is stimulated by the secretion of sucrose by epidermal cells of the stigma. There are also a number of other factors affecting growth of pollen tubes which includes temperature, pH, and concentration of calcium, boron, and metal ions such as copper and potassium ions. The pollen tube continues to grow down the style as it is attracted by chemicals produced by micropyle of the ovule. Hence, when the pollen tube penetrates the ovule, two male nuclei are released and double fertilisation occurs whereby one of the male nuclei fuses with the egg cell to form a diploid zygote and the other male nucleus fuses with the two polar nuclei, forming a triploid primary endosperm nucleus. The zygote then develops into embryo and the triploid nucleus gives rise to the nutritive tissue known as the endosperm. Immediately after fertilisation, the ovule is known as the seed.

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Figure 1: Image of pollen (Picture shows the transfer of pollen to solid medium)


MATERIALS AND  APPARATUS:

Lilum, forceps, beaker, sucrose solutions with concentrations of 0.3M, 0.5M and 1.0M, stopwatch, plasticine, 0.01% boric acid, microscope slide, dropper and microscope.

METHOD:

  1. A stamen from a Lilium flower was picked off with a forceps.
  2. The anther was gently tapped in a beaker containing 0.3M sucrose in 0.01% boric acid.
  3. A set up as in the diagram was prepared. To prepare a hanging drop preparation, the ring of plasticine (about 15mm in diameter) was placed on a microscope slide, ...

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