Sir , pls could you elaborate about the mechanism of chemotropism in the pollen tubes of an angiospermic plant?
Sir , pls could you elaborate about the mechanism of chemotropism in the pollen tubes of an angiospermic plant?
Chemo-tropism is growth of organisms such as bacteria and plants, navigated by chemical stimulus from outside of the organism or organism's part.
The response of the organism or organism part is termed ‘positive’ if the growth is towards the stimulus, or ‘negative’ if the growth is away from the stimulus.
An example of chemo-tropic movement can be seen during the growth of the pollen tube, where growth is always towards the ovules. It can be also written that conversion of flower into fruit is an example of chemo-tropism.
Fertilization of flowers by pollen is achieved because the ovary releases chemicals that produce a positive chemo-tropic response from the developing pollen tube
Plant cells are enclosed in a rigid extracellular matrix (ECM), the cell wall, through which various cell–cell communications are accomplished in response to diverse environmental or developmental signalling cues. The haploid pollen tube cell, carrying two immotile sperm cells, is the only migrating cell in the angiosperms . For plant sexual reproduction, pollen tube cells pass through a series of signalling events in female reproductive tissues and deliver two sperm cells into the embryo sac for double fertilization: one sperm cell fuses to the egg cell, resulting in the formation of the zygote, and the other to the central cell, resulting in the formation of the endosperm, a nutritional tissue for the developing embryo in the seed .
The pollen tube shows polar tip growth, which enables the tube cell to migrate directionally toward the ovules through the transmitting tract (TT) . When the pollen tube grows in the reproductive tract, a callose wall forms to sequester the cell cytoplasm containing the male germ unit (tube cell nucleus and two sperm cells) at the front. The tube cell is a completely separate unit from the spent pollen tube and the pollen grain . The tube cell cytoplasm has tip-oriented, reverse fountain streaming, which is fuelled by a dynamic cytoskeleton, to convey the vesicles containing membrane and cell wall materials to the clear zone at the newly synthesized tube tip . Here, fine actin filaments and a tip-focused Ca2+ gradient are found, and a tip-localized Ca2+-dependent protein kinase functions in oscillation and reorientation of pollen tube tip growth . In addition, a Rho-family GTPase of plant (ROP) functions in polar tip growth by controlling the dynamics of actin filament formation .
Pollen tubes grow much faster and longer in the pistil than in germination medium. The in vivopollen tubes of Lilium longiflorumare able to travel the long stylar TT (approx. 10 cm) to reach the ovules in 3 d, while the in vitro pollen tubes grow only up to approx. 5 mm and cease growth within a day. This is probably due to a more dynamic actin organization, exocytosis/endocytosis events and tip-growth signalling occurring in the clear zone at the tip by interplay between the tube cell and the pistil TT . The pistil tissues can provide the pollen tube with a cue for guidance as well as nourishment for tube cell growth. Polar tip growth and guidance of the pollen tube need to be further studied in the light of pollen–pistil interactions, because we have yet to understand fully the effects of the pistil on the pollen tube. Several studies have recently shown biochemical and genetic evidence that small proteins secreted from either pollen or the pistil play critical roles in pollen tube tip growth and chemotropic guidance . The next big question is whether these small, secreted proteins act with any receptor partner to regulate downstream signalling, as their functional counterparts do in neuronal axon guidance and polarized growth of the mating yeast cell (.
Chemo-tropism is growth of organisms such as bacteria and plants, navigated by chemical stimulus from outside of the organism or organism's part.
The response of the organism or organism part is termed ‘positive’ if the growth is towards the stimulus, or ‘negative’ if the growth is away from the stimulus.
An example of chemo-tropic movement can be seen during the growth of the pollen tube, where growth is always towards the ovules. It can be also written that conversion of flower into fruit is an example of chemo-tropism.
Fertilization of flowers by pollen is achieved because the ovary releases chemicals that produce a positive chemo-tropic response from the developing pollen tube
Plant cells are enclosed in a rigid extracellular matrix (ECM), the cell wall, through which various cell–cell communications are accomplished in response to diverse environmental or developmental signalling cues. The haploid pollen tube cell, carrying two immotile sperm cells, is the only migrating cell in the angiosperms . For plant sexual reproduction, pollen tube cells pass through a series of signalling events in female reproductive tissues and deliver two sperm cells into the embryo sac for double fertilization: one sperm cell fuses to the egg cell, resulting in the formation of the zygote, and the other to the central cell, resulting in the formation of the endosperm, a nutritional tissue for the developing embryo in the seed .
The pollen tube shows polar tip growth, which enables the tube cell to migrate directionally toward the ovules through the transmitting tract (TT) . When the pollen tube grows in the reproductive tract, a callose wall forms to sequester the cell cytoplasm containing the male germ unit (tube cell nucleus and two sperm cells) at the front. The tube cell is a completely separate unit from the spent pollen tube and the pollen grain . The tube cell cytoplasm has tip-oriented, reverse fountain streaming, which is fuelled by a dynamic cytoskeleton, to convey the vesicles containing membrane and cell wall materials to the clear zone at the newly synthesized tube tip . Here, fine actin filaments and a tip-focused Ca2+ gradient are found, and a tip-localized Ca2+-dependent protein kinase functions in oscillation and reorientation of pollen tube tip growth . In addition, a Rho-family GTPase of plant (ROP) functions in polar tip growth by controlling the dynamics of actin filament formation .
Pollen tubes grow much faster and longer in the pistil than in germination medium. The in vivopollen tubes of Lilium longiflorumare able to travel the long stylar TT (approx. 10 cm) to reach the ovules in 3 d, while the in vitro pollen tubes grow only up to approx. 5 mm and cease growth within a day. This is probably due to a more dynamic actin organization, exocytosis/endocytosis events and tip-growth signalling occurring in the clear zone at the tip by interplay between the tube cell and the pistil TT . The pistil tissues can provide the pollen tube with a cue for guidance as well as nourishment for tube cell growth. Polar tip growth and guidance of the pollen tube need to be further studied in the light of pollen–pistil interactions, because we have yet to understand fully the effects of the pistil on the pollen tube. Several studies have recently shown biochemical and genetic evidence that small proteins secreted from either pollen or the pistil play critical roles in pollen tube tip growth and chemotropic guidance . The next big question is whether these small, secreted proteins act with any receptor partner to regulate downstream signalling, as their functional counterparts do in neuronal axon guidance and polarized growth of the mating yeast cell (.
