Pollen Tube Growth & Pollen-Pistil Interaction — NEET Biology
📚 Practice ConceptPollen tube grows through the tissues of the stigma and style and reaches the ovary. You would recall that in some plants, pollen grains are shed at two-celled condition (a vegetative cell and a generative cell). In such plants, the generative cell divides and forms the two male gametes during the growth of pollen tube in the stigma. In plants which shed pollen in the three-celled condition, pollen tubes carry the two male gametes from the beginning. Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus. Many recent studies have shown that filiform apparatus present at the micropylar part of the synergids guides the entry of pollen tube. All these events–from pollen deposition on the stigma until pollen tubes enter the ovule–are together referred to as pollen-pistil interaction. As pointed out earlier, pollen-pistil interaction is a dynamic process involving pollen recognition followed by promotion or inhibition of the pollen. The knowledge gained in this area would help the plant breeder in manipulating pollen-pistil interaction, even in incompatible pollinations, to get desired hybrids.
Which of the following statements are NOT correct? S1: If the filiform apparatus of the synergids were non-functional, the pollen tube would likely fail to enter the embryo sac. S2: If both male gametes fused with the egg cell instead of one fusing with polar nuclei, a single triploid zygote would be formed, and no endosperm. S3: A plant exhibiting apomixis would produce seeds without the involvement of both syngamy and triple fusion. S4: If an ovule contains two functional egg cells and two pollen tubes enter the embryo sac, resulting in two separate syngamies, then polyembryony will occur with two genetically identical embryos. S5: In some flowering plants, the generative cell divides into two male gametes before pollen shedding, leading to a 3-celled pollen grain.
View solution & NCERT explanation
Correct answer: B — S2 and S4 only
Let's evaluate each statement: S1: The filiform apparatus plays an important role in guiding the pollen tube into the synergid. If it were non-functional, the pollen tube's entry would be impaired or fail. This statement is correct. S2: In normal double fertilisation, one male gamete (n) fuses with the egg cell (n) to form a diploid (2n) zygote. If both male gametes (n+n) fused with an egg cell (n), it would result in a triploid zygote, but the question implies *both male gametes were used to fertilise egg cells*, meaning two separate egg cells. If both male gametes (n) fertilized two separate haploid egg cells (n), two diploid (2n) zygotes would be formed, not a single triploid zygote. Also, if both male gametes fuse with egg cells, there would be no male gamete left for triple fusion, resulting in no endosperm. The statement says 'a single triploid zygote would be formed', which is incorrect. This statement is NOT correct. S3: Apomixis is a form of asexual reproduction that mimics sexual reproduction, where seeds are produced without fertilisation. This means neither syngamy nor triple fusion occurs. This statement is correct. S4: If two separate syngamies occur from two different pollen tubes (even if from the same pollen parent), the resulting embryos would be genetically distinct because the male gametes are generally not identical, and the egg cells (if two were functional) would also contribute to genetic distinctness. Genetically identical embryos typically arise from the splitting of a single zygote. This statement is NOT correct. S5: In many species, the generative cell divides mitotically to form two male gametes while the pollen grain is still in the anther, resulting in a 3-celled pollen grain at the time of shedding. This statement is correct. Therefore, statements S2 and S4 are NOT correct. The final answer is B. Recap: This question assesses the understanding of the roles of different structures and events during double fertilisation, including hypothetical scenarios and mechanisms like apomixis and polyembryony.
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