Question

1. Compare and contrast the two root partnerships described in this chapter: arbuscular mycorrhizae and rhizobia. Be sure to address the benefits received by the organisms involved in each symbiosis, similarities and differences between the fungal & bacterial strategies

2. Holoparasitic plants have lost many of the morphological and genetic traits necessary for an autotrophic lifestyle. From an evolutionary point of view, how do you think this happened (hint: apply Darwin’s 4 principles of natural selection)

Answer 1

1).

COMPARISON: 1. Both have a symbiotic relation with host plants. 2. Plants get nutrients from both. 3. Arbuscular mycorrhizae & rhizobium will get benefited by absorbing carbohydrates from plants. 4. Soil gets enriched by both. 5. Both Reproduce using host resources. 6. Both become parasites in nutrient-rich soil

DIFFERENCES: arbuscular mycorrhizae rhizobia It is a and has a symbiotic relationship with It is a soil bacteria. They grow in the roots of plant roots. They will grow in the cortical cells leguminous plants by forming root nodules. of the root. involved in the uptake of water, zinc, phosphate involved in nitrogen fixation by converting the and many other nutrients with help of hyphae atmospheric nitrogen to NH3 with help if which grow deep into the soil. It can protect the nitrogenase enzyme. plants against pathogens by creating barriers and by producing some chemicals. Associated with roots of almost 80% of vascular Mainly colonizes the roots of legumes like plants. soya bean, alfalfa.

2). A holoparasitic plant used a host plant for its fixed carbon source. and usually, they lack chlorophyll. The evolutionary event through which the parasitism developed was the development of haustoria, a highly modified root or stem of parasitic plants. Later holoparasitic behavior was established with the loss of photosynthetic machinery. From an evolutionary point of view, this might reflects Darwin's principles of natural selection. As novel environment surroundings might alter the selection pressure on genes and subgenomes. These changes including adaptive and non-adaptive might leave a measurable/ visible presence on the genome and ultimately give rise to molecular evolution.