Plant Biology Plant Primary Stems and Nutrients Lab

Plant Biology Plant Primary Stems and Nutrients Lab

Plant Biology Plant Primary Stems and Nutrients Lab

Lab 5 – Plant Primary Stems and Nutrients Introduction Stems play a vital role in the 3-dimensional life of plants. They aid plants in competing with other plants for sunlight and consequently for soil nutrients. If a plant can get tall enough and broad enough to shade out understory plants, then not only do these tall plants capture sunlight, but they prevent germination of some types of plants which might compete with them for water and other soil nutrients. The stems of plants can either be soft and green, called primary stems, or woody, called secondary stems. This lab concerns primary stems, some plant tissues, and plant nutrients. Plant Tissues Continued You have already studied epidermal tissues, parenchyma, aerenchyma, sclerenchyma, xylem, and phloem in previous exercises and we will add more tissues to our list in this lab. A good place to begin with our continued study of plant tissues is with celery stalks.

Celery plants belong to the genus Apium. Celery stalks are not actually stem tissue but are petioles, the “stalk” of the leaf. You will examine a thin section of the petiole of Apium. Activity: Cross Section of Celery Petiole Examine the cross section of a fresh, unstained petiole in figures 1 and 2. The epidermis is on the outside of the specimen and the majority of the tissue inside is ground tissue (made of parenchyma cells). Just inside the epidermis you should find bundles of cells. These dark bundles are made of collenchyma tissue and the cells that make up this tissue have primary walls thickened with cellulose. Collenchyma is a structural material that functions to keep the petioles upright. In the ground tissue you will find bundles of vascular tissue. Each bundle is somewhat triangular in shape with the narrow region consisting of xylem toward the center of the petiole. The middle portion is the functional part (sugar-conducting part) of phloem and the wider part of the triangle, toward the surface of the petiole consists of phloem fibers. Figure 1. Overview of Petiole of Apium. Figure 2. Close-up of Vascular Bundle of Apium. Look at celery that has been placed in a beaker with food coloring. Note the location of the food coloring which travels in the xylem of the vascular system.

Figure 3. Cross section of Apium petiole. The dark dots represent areas of xylem. Primary Stems Long Section of a Stem Coleus (Solenostemon species) is an attractive plant grown for its colorful leaves (figure 4). It is native to Southeast Asia and Malaysia. Examine a photograph of a prepared slide of a longitudinal section of coleus (figure 5). At the tip of the stem is the apical meristem. This is similar to the root apical meristem in that it produces new cells but in this case the apical meristem produces stem tissue. Around the apical meristem are leaf primordia. Primordia (like primordial soup) means early or beginning. A leaf primordium develops into a mature leaf. As you look down the stem you should see axillary buds which are at the nodes, or regions where the leaves are attached at the stem. If allowed to grow, axillary buds develop into branches. Figure 4. Collection of coleus plants. The surface of the stem has protoderm that turns into epidermis and most of the stem consists of ground meristem made of parenchyma cells. Ground meristem will turn into ground tissue. You may see traces of vascular tissue developing from the procambium. The procambium appears as red traces in the lateral part of the stem and it may be found going to the leaves. Eventually procambium turns into xylem and phloem. Draw the section of coleus in the following space and label what you see using the terms in this section. Figure 5. Longitudinal Section of Coleus Cross Section of a Eudicot Stem For this material we will examine a photograph of a slide of a cross section of Helianthus or sunflower stem (figure 6).

In the photograph, you will find vascular bundles occurring in rings around the stem. The xylem is on the inside of each vascular bundle. The xylem appears as large, open, red cells. The phloem is on the outside of each vascular bundle. The conducting phloem has sieve cells & companion cells. The sieve cells are larger than the companion cells that accompany them. The phloem fibers are on the outside edge of the vascular bundles and are thicker-walled than the xylem cells. The epidermis is on the outside of the stem and the ground tissue consists of parenchyma cells. The ground tissue can be divided into the pith which is in the middle of the stem and the cortex which is the outer region of the stem, from the inner edge of the vascular bundles to the epidermis. Collenchyma is found in the cortex. Figure 6. Cross Section of Helianthus stem Cross Section of Monocot Stem Monocot stems have a different appearance than Eudicot stems. Monocots seem to have arisen more recently in the fossil record as an offshoot from the Eudicot lineage. We will study Zea mays (corn) as a representative monocot (figs. 7 and 8). The majority of the stem is ground tissue made up of parenchyma cells. In this ground tissue there are scattered vascular bundles commonly known as “monkey faces.”

The xylem would be the eyes, nose, and mouth of the monkey face, the phloem is the forehead and the bundle fibers surround the face. Monocot stems also have an epidermis as the outer surface. Figure 7. Cross section of Zea mays – overview Figure 8. Zea mays Individual Vascular Bundle Axillary Buds Brassica oleracea is the scientific name for a whole host of foods that we eat. The native form of B. oleracea is wild cabbage which is native to Western and Southern Europe and has over 20 varieties derived from the original wild type including Cabbage (dense leafy heads), Cauliflower (immature flower heads), Broccoli (green flower heads), Kale (loose leafy heads), Kohlrabi (inflated stem), and Brussel sprouts (axillary buds seen in fig. 9). Examine a Brussel sprout cut longitudinally. Figure 9. Axillary Bud of Brassica oleracea. Modified stems There are many types of stem modifications. Typically when we think of a stem we think of an upright cylinder like the trunk of a tree to which branches are attached. Thorns are side branches that are narrowed into points. Some plants, such as plums and citrus, often have thorns. Sometimes the thorns occur in response to juvenile hormones and are lost as the tree matures. Others, such as bougainvillea, stay intact on the stem. Thorns may be adaptive in protecting young trees or new growth on trees from predation. Bulbs are also a type of modified stem. Bulbs such as in onion, tulip, and garlic are mostly made of leaves with just a bit of stem tissue at the bottom of the bulb.

The leaves function as storage organs as seen in figure 10. Figure 10. Onion Bulb Corms such as gladiolus and crocus are mostly stem tissue with papery leaves on the outside of the corm (figure 11). Saffron is the world’s most expensive spice and comes from the stigmas (female reproductive structures) of Crocus sativus. Figure 11. Crocus Corm Tubers are underground stems and they are represented here by potatoes. Yup, potatoes are stems, not roots. The eye of the potato is an axillary bud. Examine the sprouted potatoes in the photograph below (figure 12). Figure 12. Sprouted Potato Rhizomes are horizontal stems that generally are below ground. They are common in ferns, crabgrass, ginger, and bamboo and illustrated in figure 13. Stolons are often above ground and typically have longer sections of stem between the nodes. Examine the photo below for a rhizome. Figure 13. Rhizome of Bermuda Grass (Cynodon dactylon) Plant Nutrients When you go into a garden center and buy fertilizer for your plants there commonly are three numbers on the bag of fertilizer and these are known as the NPK ratio. N stands for nitrogen, P for phosphorus (also called phosphate) and K for potassium (K is an abbreviation from the Latin word kalium or plant ashes). These numbers are found on both organic (in this case meaning from living organisms, or naturally occurring rock) and synthetic fertilizers. The numbers represent the total weight of nutrients in the product so if you had a 20-10-10 you would have 20 grams of nitrogen, 10 grams of phosphorus and 10 grams of potassium in 100 grams of material. If nothing else is listed on the label then you have 60 grams of filler. Watch the video on how to test for nutrients using commercial tests by this link: https://youtu.be/ObMUtgu7JGQ The most complete study of plant nutrition was first done by Dennis R. Hoagland (see figure 14) at U.C. Berkeley. He was interested in studying how kelp sequestered iodine from sea water and concentrated it in its tissues at up to 1,500 times the levels in sea water. He wanted to study the impact of various elements on plant growth and, in order to do this, developed a completely artificial solution of nutrients that now bears his name – Hoagland’s Solution. He produced evidence supporting the idea that soil chemistry has a huge impact on plant physiology. He determined that the concentration of the nutrient supply is less important than the overall amount of elements supplied to the plant. If given dilute solutions in adequate volume the plant can absorb those elements. He also recognized that oxygen is important for mineral absorption. When oxygen is reduced such as in waterlogged soils, the roots die and cannot absorb nutrients even if they are available to the plant. Plant Biology Plant Primary Stems and Nutrients Lab

If plants are overwatered they often have the same symptoms as plants that are dry leading some people to water the plants even more! Figure 14. Dennis R. Hoagland Nutrient Experiment There is a phrase which might help you to remember the macronutrients required by plants and this is CHOPKiNS CaFe Mg (C. Hopkin’s Café, mighty good). This is a shorthand notation for Carbon, Hydrogen, Oxygen, Phosphorus, Potassium, (the “i” is a place holder), Nitrogen, Sulfur, Calcium, Iron (Fe is the Latin abbreviation for Iron – Ferrum) and Magnesium. Plants also require micronutrients and some of these are boron, copper, molybdenum, and zinc. The concentration of micronutrients is less than 0.1% but they are essential for plant growth. In cases of copper and zinc, even though they are essential micronutrients, they can be unhealthy to plants in higher concentrations. Some elements such as cadmium and lead are not used at all by plants and are considered toxic elements. Modern day companies have formulated their products from the research done by Dennis Hoagland. The following list is an analysis of Miracle Gro ® Plant Food. Nitrogen (N) 24% Phosphorus (P) 8% Potassium (K) 16% Boron (Bo) .02% Copper (Cu) .07% Iron (Fe) .15% Manganese (Mn) .05% Molybdenum (Mo) .0005% Zinc (Zn) .06% Activity: Nutrients It is valuable to know what deficiencies your plants may have, particularly in large agricultural plots, but also for the home gardener as well. Study the descriptions of the nutrient deficiencies below and match them to the photographs in questions 9-13 in the Review Section at the end of this lab manual. Plant Biology Plant Primary Stems and Nutrients Lab

Nutrient Deficiencies and Their Symptoms in Plants N – Short plants, older leaves pale yellow-green P – Stunted plants, dark green leaves K – Older leaves yellowed, scattered dark spots Fe – Distinct yellowing between leaf veins (veins stay green) on new growth Mg – Older leaves develop yellow areas between veins, less distinct than Fe. Review Section 1. Label the cross section of stem below 2. Label the longitudinal section of shoot below. 3. What is the difference between a primary stem and a secondary stem? 4. What kinds of plants have scattered vascular bundles? 5. What is the difference between a bulb and a corm? 6. What is the tissue that makes up the cortex and the pith? 7. Write what the image is below and label the parts. 8. Is a macronutrient one that is heavier than a micronutrient? Symptoms of Nutrient Deficiencies in Tomato Plants Match the nutrient deficiency with the following photos. N – Short plants with older leaves pale yellow P – Stunted plants, dark green leaves K – Older leaves yellowed, scattered dark spots Fe – Distinct yellowing between leaf veins (veins stay green) on new growth Mg – Older leaves develop yellow areas between veins, less distinct than Fe. 9. 10. 11. 12. 13. Image Sources Figure 4. https://www.calloways.com/coleus/ Review Exercises 9-13 – https://www.haifa-group.com/crop-guide/vegetables/tomato/cropguide-tomato-plant-nutrition …