Submitted by Lucas Maria Keoni Letelier The diversity of Oryza sativa L. is an oft forgotten yet definitive human concern. Our partnership with this group, lasting thousands of years, has seen the drawing out of the best qualities of the plant and the development of some of the more regrettable practices in the animal. Now, our actions have restricted our ability to cultivate some of our more popular varieties of rice and we must turn to obscure strains in order to develop new breeds combining high yields with salt and drought tolerance. In a warming planet, where unsustainable agricultural practices are steadily salting our soil, these qualities could expand our food production and provide one solution to an ever-looming, multi-faceted food crisis. In order to select the correct candidate in this breeding project, it is important to have a solid understanding of the traits that we are seeking out. It is one thing to understand that a plant does well in submerged or saline conditions, it is a different thing all together to know and understand the morphology that allows for this. Enter our class and seven rice varieties, three of which were breeding lines (Nipponbare, IR29 and N22) and four were land races (Kalo gorah, Nona Bokra, Pokkali, and Talmugur). We divided these varieties among the class, and recorded several key features. Of the shoot, we photographed and recorded the length of ligules (Fig. 1), we then took cross sections of the main blade 15cm, 10cm, and 5cm above the collar as well as 5 cm below the collar. These cross sections were stained with toluidine blue and the main veins were counted, as well as the number of aerenchyma chambers, occurence of silica in these, presence of sclerenchma along the abaxial side, and the occurence of abaxial bulliform cells. An example of one such cross section can be seen in Fig. 2. The roots were treated similarly; first the length from the bottom of the pot to the tip of the root was recorded, then the roots were counted and a representative was removed for cross sectioning. In order to understand the development of aerenchyma cavitation in maturing root tissues, cross sections were prepared from the bottom of the pot, 5cm, 10cm, 15cm, and 20cm from the bottom and 2cm from the tip of the root. These were also stained with TBO (Fig. 3) and proportion of aerenchymatous cortex was recorded with a characterization of clustered or diffuse arrangement, where possible. This was likely the most difficult preparation for the Pokkali group as the aerenchyma developed very quickly in these, already being visible in ~80% of tissue at the youngest section (nearest to the tip). At times, it felt like trying to cross section a plastic straw, with lots of splitting and flattening as we went. This data was all compiled online and will be used to elucidate the connections between these traits and the survival of the rice varieties under adverse conditions. Fig 1. The collar and ligule of the Pokkali variety, notice the absence of auricles. (Credit: Alex Abair) Fig 2. A cross section at 5 cm above the collar of a Pokkali, with silica crystals. notice the asymmetrical lengths of the blade on wither side of the "midrib" (top and bottom). (Credit: Alex Abair) Fig 3. A cross section from the middle of the root (~15 cm from the bottom of the pot) notice the well developed empty spaces within the cortex. (Credit: Alex Abair)
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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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