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Factors afftecting growth of pollen grains

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Introduction

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. ...read more.

Middle

0.3M sucrose + boric acid 0.5M sucrose + boric acid 1.0M sucrose + boric acid 30 9 x 9.9�m = 89.1�m 10 x 9.9�m = 99.0�m 10 x 9.9�m = 99.0�m 60 10 x 9.9m = 99.0�m 11 x 9.9m = 108.9�m 15 x 9.9m = 148.5�m 100 division graticule = 99 division stage 1 division graticule = 0.99 division 1mm = 100 division stage micrometer (�m) 1 small division = 0.01mm DISCUSSION: 1. Lillium anthers were chosen in this experiment because they have nice meiotic figures as they produce the male gametophyte, that is, the chromosomes are more easily observed than in many other species. 2. To investigate the factors which affect pollen tube growth, the concentration of sucrose factor for an example, pollen grains are placed in a sucrose solution and the pollen tubes which germinates is then observed and measured. The length of pollen tube indicates how well the factor affects pollen tube growth. 3. In this experiment, the anther was first gently tapped to remove small pollen grains that are barely visible to the human eye into the beaker containing the different concentrations of sucrose and boric acid. 4. By using the different concentrations of sucrose, we can determine the effect of sucrose on germination of pollen grains. ...read more.

Conclusion

8. During the experiment, some pollen grains had two pollen tubes emerging from it in different directions. This happens as the pollen tube has no specific direction (usually they are attracted the chemicals produced by the micopyle of the ovule). The truth is that pollen tubes can germinate from 1, 2 or 3 poruses of the pollen grain, divide and branch during their growth in the ovary. The branches are of different length and give secondary splits. Special short branches are formed near the micropyle of the ovule. They grow into top part of integuments. The pollen tubes start to branch profusely near the placental surface. In that place they are likely to react to the stimulus from mature ovules which seem to be dispersed in the exudate covering placenta. 9. The hanging drop technique is used in this experiment as it is a well-established method for examining living, unstained, very small organisms. The traditional procedure employs a glass slide with a circular concavity in the centre into which a drop of fluid, containing the pollen grains, hangs from a coverslip. This simple preparation allows students to observe extremely small sized pollen grains in sucrose solution under the microscope effectively and easily. CONCLUSION: As concentration of sucrose increases, the number of pollen grains which have germinated (pollen tube) also increases. ...read more.

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