Question

did the agar (non-nutrient) serve in the carrot gall experiment 7. Have you ever observed galls in nature? Examine closelystems and leaves of the very large trees on Kissena Boulevard (Pin Oaks) and on 150th Street (English Planes or Sycamores). Do you think these galls are caused by Agrobacterium? Look up "plant galls" or "lant gall types on the internet to discover alternate causative agents and mechanisms of formation 8. How did gene transfer differ in the pGlo and Agrobacterium experiments ?

Answer 1

Galls are a kind of swelling growth on the external tissues of plants, fungi or animals. Plant galls are abnormal growth of differnt parts like leaves, twigs, roots, flowers, etc. Eg- eucalyptus leaf gall, oak artichoke gall, etc. Plant galls are caused by various parasites like fungi, viruses and bacteria. Agrobacterium tumefaciens is a gram negative bacterium which causes crown gall disease in many dicot plants like grapes, stone fruits, sunflower, cotton, soyabean, etc. The other causative agents of plant galls include insects and mites (gall wasps, aphids), fungi (rust fungi), viruses (Nephotettix nigropictus), bacteria (Pseudomonas savastanoi) and nematodes.

Agrobacterium tumefaciens invades plants at the site of wound.Once the bacteria have entered the plant, they occur intercellularly and stimulate surrounding tissue to proliferate due to cell transformation. Agrobacterium performs this control by infecting the plant through its Ti plasmid. The Ti plasmid integrates a segment of its DNA known as T-DNA into the chromosomal DNA of its hoat plant cells. To transfer the T-DNA into the plant cell, Agrobacterium uses a certain mechanism for the formation of T-pilus. With the formation of T-pilus,the T-DNA transform normal plant cell into tumor and direct these tumor cells to produce the chemicals required by the pathogen. To cause gall formation, the T-DNA encodes genes for the production of auxin or IAA and genes for production of cytokinins are also expressed. This stimulates cell proliferation and gall formation. These tumors exert significant pressure on the surrounding plant tissue which causes the tissue to become crushed.