By: Chelsea Maddox Just this last week in lab on Thursday, February 16th we took a look at structure of roots and their external features. From what we have learned so far about roots is that they have many functions. One: they anchor the plant to a substrate. Two: absorb water and minerals. Three: they conduct water, mineral, and carbohydrates. Four: roots store the carbohydrates while playing an additional role in asexual reproduction. The external features and structure of roots is very important because they are associated with how they carry out the above functions. Plants have two types of branched root systems. One being a fibrous root system and another being taproot system. Angiosperms have been classified into two major groups known as monocots and dicots. The monocots is associated with a fibrous root system because they are commonly short-lived so they are composed of adventitious, branched roots. So you've probably guessed by now, dicots are associated with the taproot system because the plants strive to live longer. The taproot system has a primary root that develops as a taproot which then gives rise to secondary, adventitious, branched roots. The images I am going to show below are of corn (Zea mays), a monocot with a fibrous, adventitious root system.
Unlike corn (Zea mays), a broad bean plant (Vicia faba) is a dicot with a taproot root system. Even though the root system isn't fibrous, it is still considered to have adventitious, branched roots. Below are some images I took in lab on Thursday, February 16th of the mature broad bean plant. Unfortunately, I am unable to label the close up view of the dicot broad bean with the taproot system because it just looked like mess because the picture I have of the root are bunched together too tight. However, to the left, I have uploaded an image of the broad bean root system labeled for a better understanding of the difference between monocot and dicot root. Numbers 4 and 5 I feel do a great job pointing out which part is what in these figures. One thing I found interesting in class and I was highly encouraged to present within this blog is the unique nitrogen-fixing organs that result from a symbiotic interaction between the plant and nitrogen fixating bacteria known as root nodules. Most legumes result in infection by bacteria of the host-plant root. More information of how the process of infection begins you can gather from recommended reading (Ch. 29, pgs. 693-700 in Raven's Biology of Plants). Assuming the recommended reading was done before lecture on February 9th, you may remember reading about the two different types of root nodules. They can be distinguished by either indeterminate or determinate. Indeterminate root nodules are elongated and cylindrical due to the presence of the meristem. However, the determinate root nodule is presented in spherical form due to the lack of the persistent meristem. The image I will be showing you below is of indeterminate root nodules on the roots of a mature broad bean plant. These nodules on the mature broad bean are common of the legume (Fabaceae) family. "Legumes secrete compounds called flavonoids from their roots, which in turn trigger the secretion of nod factors in the rhizobia. Coming full circle, the nod factors spark a reaction in the legumes, causing the roots to swell and form the nodules you see here. It is within these nodules that rhizobia live in harmony with their host plant."
Read more at http://www.gardenbetty.com/2012/11/a-look-at-legumes-rhizobia-and-root-nodules/#ZV650Ij8EhVTtrGs.99 The coolest part about lab on Thursday was getting to cut open the root nodule on the broad bean plants while examining it under the dissecting microscope. When cut open, the nodule represented a pinkish/red color (pictured below). The nodule having the color inside represents the presence of leghaemoglobin which means the nodule is active and is fixing a lot of nitrogen for the plant. FUN FACT: the redder the nodule, the more ACTIVE it is!
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AuthorContent is created by students participating in the Plant Structure course at Oregon State University for Winter 2017. Archives
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