Question

1. Explain both the ways in which signal transduction can happen inside a plant cell 2. Explain any 2 ways in which a plant will avoid self-fertilization

Answer 1

Q 1. Explain the ways in which signal transduction can happen inside a plant cell?

Answer: The external stimuli/signal (light/chemicals) are perceived by the plant cells and responded by them by changing their gene expression associated with the morphogenesis/development (shoot or root development/photosynthetic regulation/flowering/fruit ripening/germination) of the plants. There are receptors on the cell surfaces, which sense the signals and by using complex network, they transmit it the nucleus.

These signaling pathways (by which signal is transmitted to the nucleus) are as follows:  

(1) GTP binding proteins (G proteins): Many transduction pathways with numerous signals such as Auxin, phytochromes, light, response to pathogens (bacteria and fungi) utilise heterotrimeric GTP binding protein in signal transduction pathway. The signals directly alters the activity of DNA-binding proteins in the nucleus and regulate gene expression. If readers require detailed knowledge about this pathway, they can read the following article:

Assmann, Sarah M. “Heterotrimeric and unconventional GTP binding proteins in plant cell signaling.” The Plant cell vol. 14 Suppl,Suppl (2002): S355-73. doi:10.1105/tpc.001792.

(2) Protein kinase cascades: In this pathway, many proteins are sequentially phosphorylated and activated. Tis pathway. This pathway is activated due to biotic and abiotic stress and cell division, hormones or developmental process. They also alter gene expression and cause substative changes. For more information about this pathway, readers are requested to go through the following article:

Kazuya Ichimura, Kazuo Shinozaki, Guillaume Tena, Jen Sheen, Yves Henry, Anthony Champion, Martin Kreis, Shuqun Zhang, Heribert Hirt, Cathal Wilson, Erwin Heberle-Bors, Brian E Ellis, Peter C Morris, Roger W Innes, Joseph R Ecker, Dierk Scheel, Daniel F Klessig, Yasunori Machida, John Mundy, Yuko Ohashi, John C Walker,
Mitogen-activated protein kinase cascades in plants: a new nomenclature, Trends in Plant Science, Volume 7, Issue 7, 2002, Pages 301-308, ISSN 1360-1385, https://doi.org/10.1016/S1360-1385(02)02302-6.

(3) Membrane Ion channels: The plant cell mainly contain CLC chloride transporters/channel, potassium channels, ionotropic glutamate receptor homologs, cyclic nucleotide–gated channels. These channels facilitate the stomatal opening and closing, gaseus exchange in the plants, tolerance to different metals etc. For better understanding of this pathway, readers are requested to go through the following article:

Ward, John M et al. “Plant ion channels: gene families, physiology, and functional genomics analyses.” Annual review of physiology vol. 71 (2009): 59-82. doi:10.1146/annurev.physiol.010908.163204.

Q 2. Expalin any two ways, in which a plant will avoid self fertilization?

Answer: Plants utilize various mechanisms to avoid self fertilization.

(1) Some of the plants such as Salix sp., Phoenix dactylifera avoid self pollination by becoming dioecious. In this condition, male and female plants are different. Hence, exclude the probability of self pllination.

(2) Some monoecious plants where staminate and pistillate flowers are present on the same plant and hermaphroditic flower where both parts present on same flower avoid self pollination by the process of dichogamy and protogyny. Dichogamy is the condition in which pollens are either shed before the sigma is receptive or after that and prevent the plant from self pollination. In protogyny, the pistils of the plants mature first than the pollen and avoid self pollination.The Dichogamy condition is well reported in Epilobium angustifolium and Salvia sp. while Protogyny in arum lilies, grasses etc.