The effect of mineral deficiencies on plants
Objectives:
To investigate the effect of plant mineral deficiencies.
To develop problem solving and experimental skills, for example, information is accurately processed, experimental procedures are planned, designed and evaluated properly, and producing valid results and recording results.
To develop careful observing skills on the development changes occurred on Lemna leaves.
Introduction:
Lemna
Lemna are small, free-floating aquatic water plants found in ponds.
Lemna has been used for testing toxicity of certain chemicals.
Lemna can be transformed by molecular biologist to express proteins of pharmaceutical interest.
Chlorosis (break down of chlorophyll) happens when a plant deprived of certain nutrients such as nitrogen, magnesium, and iron. Chlorosis can be noted by yellowing and decolourising of the leaves. This is because the breakdown of chlorophyll a and chlorophyll b (both green in colour) may reveal other photosynthetic pigments. They are xanthophylls (yellow) and carotene (orange).
Necrosis happens due to chlorosis. The leaves may have brownish or blackish patches. Some examples of deficiencies that lead to necrosis include Boron deficiency, and Calcium deficiency. Some other symptoms involve other mineral deficiencies include dark green leaves, short and brown roots, brittle petioles and mottled leaves (spots on the leaves). Plant symptoms may appear in leaves, stems, roots, flowers, fruits, and seeds.
For deficiency in manganese, a mild chlorosis can be developed along the veins and young leaves. At the early stage, these symptoms are very similar to iron deficiency. Manganese is an important component of enzyme Z in light dependent reactions. The lacking of phosphorus show can show necrosis. However, the major visual symptom is that the plant is stunted or dwarfed. The lacking of sulphur shows a general overall chlorosis while still retaining some green colour. The lacking of potassium can show marginal necrosis where necrosis is happened around the tip of leaves.
Photosynthesis
Photosynthesis is a metabolic pathway that utilise the carbon dioxide into organic compounds especially sugars using the energy from sunlight. The sugars are transported in the form of sucrose plants and stored as starch. Furthermore, sugars can be modified to form other substances including amino acids and lipids. Photosynthesis occurs in plants, algae, and many species of bacteria. Photosynthesis is crucially important for life on Earth, as well as maintaining the normal oxygen level in the atmosphere. Photosynthesis takes place in the organelle chloroplasts where chlorophyll is found there. Photosynthetic organisms are called photoautotroph which means they are able to synthesis food from inorganic substances.
The process of photosynthesis can be divided into light dependent reaction and light independent reaction (Calvin cycle). Chlorophyll a pigment molecules are also known as P700 in Photosystem I and P680 in Photosystem II. Fixation of carbon dioxide and photolysis of water occurred in photosynthesis. The overall general equation of photosynthesis is shown below:
6CO2 + 12H2O + light energy → C6H12O6 + 6O2 + 6H2O
Hypothesis:
The Lemna plant will thrive in the complete culture solution to produce the greatest number of leaves while significant poor growth will be shown in the cultures that are lacking of nitrogen, calcium, and magnesium. This is because nitrogen, calcium, and magnesium are macronutrients which are required by plants in large amount while the remaining nutrients are needed in small amounts only for the growth of the plant.
Variables:
Manipulated variable: The deficiencies of different types of minerals
Responding variable: Growth of Lemna leaves
Fixed variable: Light intensity, Surrounding temperature and humidity, concentration of carbon dioxide in the air, volume of culture solution, initial concentration of minerals present in each culture solution, initial number of Lemna leaves in each culture solution, types of Lemna plants, pH of the solution
Apparatus and materials:
8 Petri dishes with a range of nutrient solutions, including solutions with:
all nutrients present
lacking nitrogen
lacking potassium
lacking magnesium
lacking calcium
lacking iron
lacking phosphorus
lacking sulphur
Distilled water
a dropper, a measuring cylinder, forceps, stereo microscope, stickers for labelling, Petri dish covers
Procedure:
The Petri dishes are rinsed with water and wiped dry.
20cm3 of each nutrient solution is added into each Petri dish.
5 Lemna plants are then scattered into each Petri dish.
The Petri dishes are then covered.
All the Petri dishes are arranged in a tray and put it under a shed along the corridor.
Observations regarding the colour of the leaves and the size of roots are taken. The number of healthy leaves are counted and recorded.
The observations are repeated every 2 subsequent days for 14 days.
The results are recorded in a table for a comparison to be made between different conditions of plants.
Risk assessment:
Ensure that the Lemna plants do not adhere to the wall of the cover. If it is stick to the wall of the cover, use a sterilised forceps to transfer it back to the nutrient solution.
Use sterilised forceps to transfer the plants and avoid your finger from touching the nutrient solution and the plant to prevent contamination.
After a few days of observations, some water droplets may be found condensed on the cover. Wipe the cover dry to give a clearer observation.
Result:
Day of observation
Type of
culture solution
Day 1
Day 4
Day 7
Day 9
Day 11
Day 14
All nutrients present 5 8 11 15 19 37
Lacking Calcium 5 10 10 10 9 9
Lacking Iron 5 7 14 16 23 41
Lacking Potassium 5 5 7 8 15 24
Lacking Magnesium 5 5 6 6 10 12
Lacking Nitrogen 5 4 4 4 4 7
Lacking Phosphorus 5 5 5 5 7 11
Lacking Sulphur 5 6 9 12 19 27
Lacking of nutrients 5 5 0 0 0 0
Number of leaves
Type of culture solution Observation after two weeks
All nutrients present Roots present in all leaves. (Long roots)
Lacking Calcium Roots present in all leaves. (Long roots)
Lacking Iron Roots present in five leaves. (Short roots)
Lacking Potassium Roots present in three leaves. (Short roots)
Lacking Magnesium Roots present in five leaves. (Short roots)
Lacking Nitrogen No roots present.
Lacking Phosphorus No roots present.
Lacking Sulphur Roots present in thirteen leaves. (Short roots)
Lacking all nutrients No roots present.
Number of roots
Conditions and colour of leaves
Day of observation
Type of
culture solution
Day 1
Day 4
Day 7
Day 9
Day 11
Day 14
All nutrients present Green and healthy Green but a handful of the leaves have little white spots. Green. White spots are still present but very few. Same observation as before. Leaves seem to become larger. Same observation as before. Same observation as before.
Lacking Calcium Green and healthy Slightly decolourised Completely decolourised Completely decolourised Completely decolourised Completely decolourised. Some appeared to be translucent. The leaves are dead.
Lacking Iron Green and healthy Each and every leaf has a little yellow spot. Most of the leaves have yellow spots Many have buds but become slightly smaller. Some have tiny yellow spots but not significant. Observation is about the same as the previous one. The intensity of the green colour reduces a little bit. Not much difference from the previous observation except that the leaves have more yellow spots.
Lacking Potassium Green and healthy One yellowed while three have little white spots. Mostly are green but there are still some white spots present on some leaves. Still green but one of the leaves has part of it conspicuously turned white. Apart from the whitened leaf, all leaves are green in colour. No obvious white spots could be found. All appear to be green.
Lacking Magnesium Green and healthy Three lost their green colour while the other two have white spots
All the leaves have reduced in size. Same as the previous observation. More white spots can be seen. All the leaves are small except one. Two plants have one of their leaves decoloured. Only two plants seem normal and healthy, the rest have their leaves turn pale. All the leaves are small except one. Three plants have decolourised completely and turn slightly translucent. Three more plants have one of their leaves decoloured too. The rest are pale in colour. Most of the leaves are small.
Lacking Nitrogen Green and healthy Some leaves turn slightly yellowish a little bit. White spots present on some leaves. Same observation as the previous one. Most of the leaves are yellowish green in colour. There is loss of colour to a certain extent. Some white spots are obvious but not many. The leaves are light green in colour. Light green leaves with only a little number of white spots.
Lacking Phosphorus Green and healthy No obvious change could be observed. Green. Every leave has white spot on it. Every leave has white spot on it. Every leave has white spot on it. Most leaves have white spots.
Lacking Sulphur Green and healthy Green. A few white spots could be observed but not obvious. Same observation as in day 4. Same observation as in day 7. Basically there is no white spot could be found but some of the leaves turn paler. No white spots could be found. Only one leaf turned yellowish while some of the rest are slightly light green.
Lacking all nutrients (distilled water) Green and healthy All leaves are decolourised. All leaves are dead. All leaves are dead. All leaves are dead. All leaves are dead.
Discussion:
The using of Lemna
The using of miniature Lemna plants are ideal for investigating the effect of plant mineral deficiencies. Lemna can easily acclimatize them to the new environment therefore, it is easy to grow them in Petri dish containing nutrient solution. Furthermore, Lemna plants can be cultured in large amounts for reliable statistical data to be collected.
Controlling of variables
The amount of exposure to sunlight is controlled by placing the Petri dishes at the same places where the daily exposure to sunlight is nearly a constant. The Petri dishes are covered to maintain the temperature, the carbon dioxide concentration, and humidity surrounding the plants in the Petri dishes. The volume of the solutions is maintained in the Petri dishes to ensure that the rate of photosynthesis is not affected in each Lemna plants. The initial concentration of Lemna should be the same for all Petri dishes because the amount of nutrients available can affect the growth of the Lemna plants. There must be the same number of Lemna plants available in each Petri dish because the same level of competition should be maintained for all Petri dishes so that this factor will not affect the level of Lemna plant growth. There are 13 species of Lemna plants. Therefore, the same species of Lemna plants are selected in the experiment because different species of Lemna plants may result different levels of competition. Furthermore, healthy plants of the same age should be chosen to maintain the fixed variable. Besides, pH should be optimal for the growth of Lemna plants.
Explanation of experimental procedures
The Petri dishes are rinsed with water and wiped dry to prevent the fungal or bacterial contamination. The contamination may damage the plant or making the plants deprived of nutrients. 20cm3 of solution is added in order to give a constant supply of nutrients to the plants. 5 Lemna plants are scattered as far as possible in each Petri dish so that the competition for space can be omitted. The Petri dishes are covered to prevent bacterial and fungal contamination. The Petri dishes are put under a shed to ensure a moderate intensity of sunlight can reach for the Lemna plants.
Improvement of experimental methods
The experiment is best carried out in a greenhouse because the all growing conditions are well controlled. The intensity of light can be controlled more efficiently by using a light bed of fluorescent tube lights which will be used to produce uniform light, 24 hours a day. The growing room is automatically heated to an average temperature of 25℃. A larger sample of plants can be used in this experiment to ensure a reliable result is generated. The amount of moisture present in air can be controlled by keeping the humidity in the room near 100% at all times. Besides, hydroponics can also be used to investigate the mineral deficiencies in plants.
The changes in colour on the Lemna leaves can be difficult to observe because the leaves are small and small spots of decolourising are easily neglected. This problem can be overcome by using a stereo microscope where a magnification of 2X and 10X are available for checking against your observations and fungal contamination. The Petri dishes can be placed directly under the microscope for observations to be made. Furthermore, high resolution photographs can be taken each time the observation is made for future reference. Sodium hydrogen carbonate can be added to the nutrient solution to order to saturate the air the Petri dishes with carbon dioxide. It is ideal that to prevent salt accumulation and nutrient depletion, nutrient solutions were changed every week and distilled water was added periodically to maintain solution volume.
Evaluation on procedures and results
The experiment is valid and reliable because we have considered all the possibilities where the absence of different minerals is investigated. Furthermore, the observations are done consistently every two days. The fixed variables are well controlled. Besides, controlled experiments have been set up to investigate what happens to Lemna plants when immersed into complete nutrient solution and distilled water. This is ensuring that abnormal plants are due to certain mineral deficiencies. Replicates of the experiment are needed to minimize the errors of the results and to ensure the results are true.
However, there are some anomalies in the results because we have chosen plants of different ages. We may even choose plants with poor health conditions. We suspect that the plants treated with iron may have greater ability of taking up nutrients than plants in the complete culture solution, making the number of plants of former less than the plants in culture lack of iron. Furthermore, light intensity may not be constant because weather patterns are fluctuating. On a rainy day, there may be not sunlight. Furthermore, the nutrient solution in the Petri dishes can dry out at different rates. Carbon dioxide concentration and temperature can fluctuate due to changing weather patterns. Besides, each plant has its own rate of photosynthesis. They have period where the activity of photosynthesis is very high (usually in the afternoon) and a period of low photosynthesis rate (usually at dawn or dusk). In addition, the anomalies can be caused by our wrong judgments on the colour of the leaves. During our observations, we can see leaves with pale green and dark green colour. However, we cannot judge which leaf is healthy. Some slides which are contaminated by fungal or bacterial contamination can influence our results too. Admittedly, the nutrient in the Petri dish may be use up by plants where we can see the plants in the complete culture solution has some white spots on them.
Explanation and analysis of results
From the results, it is obvious that the lacking of iron has the least effect on the growth of Lemna plants whereas the lacking of nitrogen has the most effect on the growth of Lemna plants. This is because at the end of our observation, we found out that there are only 7 Lemna plants left after 14 days for nutrient solution lacking nitrogen whereas there are 41 Lemna plants remaining for nutrient solution lacking iron. This means that iron is most probably a micronutrient for the Lemna plant while for nitrogen, it is the macronutrient. Therefore, nitrogen is the most important nutrient required by plants.
The lacking of nitrogen can cause chlorosis because nitrogen is essential for the formation of amino acids, proteins, and chlorophyll. Chlorophyll is the pigment that keeps plants green. The loss of chlorophyll can cause the colour of the leaves to turn yellow and eventually decolourises. Furthermore, the growths of plants are retarded due to the lack of protein which is essential for growth. Furthermore, the roots are also reducing in size and dying. At the end of our observation, we found out that the leaflets decolourised and started to decompose and there aren’t any roots visible.
Magnesium is another vital component of chlorophyll in plants. It is located in the central region of porphyrin head of chlorophyll, where 4 nitrogen atoms are bonded to it.
Source:
This is a type of chlorophyll, chlorophyll a, found in every plant where its molecular formula is C55H72O5N4Mg. Magnesium has variable oxidation states and can donate or accept electrons. From the molecular formula shown, it is obvious that magnesium and nitrogen are essential parts of chlorophyll. Without magnesium, chlorosis will also occur where the colour of the leaves can turn yellow and eventually decolourised.
For the culture solution without iron minerals, the Lemna plants are not very much affected. The plants even thrive in this condition and the number of leaves even greater than the plants in complete culture solution although the size of leaves and roots are smaller. This shows that the presence of iron may be needed by the plants in very small quantity but it can survive for a long time without it. However, some yellow spots are noted on young leaves due to chlorosis. This is most probably because iron still has some minor roles in the formation of chlorophyll besides responsible for the respiration and metabolism of the plant. Iron is a component of ferredoxin (iron sulphur proteins) that mediates electron transfer in light dependent reactions in plants.