Plant Physiology and development
Plant Physiology and development
This unit wasn't really broken up into lectures - as in they just continued on from each other and the notes are presented all in one documents, so I'll just make breaks where I think it's convenient. The unit is broken up in to two parts. Plant Structure and function, and plant development.
Plant Structure and Function
Nutrients
There are 17 essential nutrients for plants. They are divided in to macro and micro nutrients depending on the quantities needed. Different species of plants require different amounts of each nutrient and some specific nutrients require nutrients not on this list - these are just ones that are required by all plants. Their impact varies but they are essential because a plant cannot reproduce without these nutrients (either directly, or because it needs them to live).
Macro nutrients are as follows; H, C, O, N, K, Ca, Mg, P, S.
Micro nutrients are as follows; Cl, Fe, B, Mn, Zn, Cu, Ni, Mo.
They are divided in to classes as follows;
Nutrients essential for organic component of plants;
C, H, O - in all organic molecules
N - in amino acids
S - in the amino acids cysteine and methionine and therefore in proteins, hormones and coenzymes.
Nutrients that store energy or ensure structural integrity
P - in sugar phosphates, ATP, NADPH2, nucleotides, phospholipids, etc.
B - Important constitute of cell wall matrix. Involved in cell elongation and nucleic acid synthesis.
Si - Not essential. Deposited in cell walls of some plants.
Nutrients that remain in ionic form;
K - important for maintaining osmoticum, also keeps electrochemical balance. Required for the operation of many enzymes.
Na - Non Essential. Required for C4 and CAM photosynthesis. Can substitute for K in some reactions
Mg - Constituent of chlorophyll. Required for the operation of many enzymes, particularly Rubisco.
Ca - Constituent of cells walls, required for signalling cell division. Required by enzymes, metabolic regulator.
Mn - Required for photosystem II function, required by many enzymes.
Cl - Required in photosynthetic reactions.
Nutrients involved in electron transfer
Fe - constituent of proteins involved in the photosynthetic, respiratory and nitrogen fixing electron transfer.
Cu - Component of plastocyanin, cytochrome oxidases and other enzymes.
Zn - constituent of dyhydrogenase enzymes and the like.
Mo - required for N2 fixation electron transfer, nitrate reductase
Ni - required for N2 fixing bacteria, used in urease.
It's important to know if a particular element is limiting growth/deficient. Soil analysis is a poor predictor - nutrients can be in the soil but not available, or sequestered from the atmosphere instead of the soil. Plant tissue analysis is more helpful.
Plants typically have a sharp impact of a lack of nutrients, then a large area where changing the nutrient amount has no impact, and then face toxicity problems if they get too much of the nutrient.
Nutrient-growth relationships are species and specific. They also can be a factor determining plant distribution. Required for economical crop production and the prevention of eutrophication.
Inadequate supply of nutrients can lead to stunted leaves, roots or stems, necrosis or chlorosis.
Deficiency symptoms depend on the functionality of the nutrient and the ability of the plant for elemental translocation from old to new parts.
Nutrient withdrawal symptoms are determined by the mobility of the nutrient in phloem. High mobility are N, K, P, Mg, Cl. Intermediate are Zn, Cu, Mn, Mo. Low - B, Fe, Ca.
Mobile elements show their symptoms of deficiency first in old leaves because the plant can move elements it does have to its newer leaves. Immobile elements show their deficiency symptoms in the new leaves first because it can't move old and already used elements there.
Deficiency symptoms;
Nitrogen. Very common deficiency, lots of soils have poor nitrogen. Symptoms are chlorosis of old leaves, often with a purple colour. Excess N can lead to a high shoot to root ratio, and also retards the seed set.
Phosphorus. Often limited in soils, and especially in Australian soils. Symptoms are stunted growth, dark green leaves, old leaves become brown and die. Delayed maturity.
Potassium. An important osmoticum. Symptoms are chlorosis of old leaves, necrosis and in cereals a loss of stalk strength leading to grain falling over etc.
Sulphur. Australian soils can be very poor in it. Mainly found/recycled in amino acids. Deficiency causes chlorosis including veins. Mostly appears first in young leaves.
Magnesium. In chlorophyll and important for enzyme regulation. Causes interveinal chlorosis in old leaves first. Rare to be a limiting nutrient.
Calcium. Usually sufficient in soils. Usually not found in acid soils - can be treated with by using lime. Has low mobility. Deficiency causes deformities - lack of cell division.
Chlorine. Most plants absorb 10 to 100 times more chlorine than they need, so deficiency is rare. Causes growth reduction, wilting, chlorotic and nerotic spots.
Iron - Deficiency causes severe interveinal chlorosis. Occurs in young leaves first. Leaves can turn white over time.
Manganese - Deficiency causes interveinal chlorosis, necrotic lesions and disorganised thylakoid membranes.
Nutrients can be present without being available to plants.
Nutrient availability can be dependent on soil pH. Micronutrient cations such as Cu2+, Fe2+, Zn2+ and Mn2+ can have low availability in neutral and basic soils because the cations bond with OH- anions. Changing the pH can make soil anions unavailable to the plant. A better option is to use chelating agents (ligands).
Plants prefer Fe3+ to Fe2+ but Fe2+ is more soluble in water and some plants can reduce iron when it's limited. They do this by releasing reductants and/or by acidifying the soil (releasing H+ ions).
Toxicity
Plants can be tolerant of toxicity in three main ways; Avoiding the substance, isolating it in compartments or by genuine tolerance.
Toxicity is hard to decipher as toxicity in one element can create deficiencies in other substances. It's also possible that multiple elements are in toxic concentrations.
Nutrients
There are 17 essential nutrients for plants. They are divided in to macro and micro nutrients depending on the quantities needed. Different species of plants require different amounts of each nutrient and some specific nutrients require nutrients not on this list - these are just ones that are required by all plants. Their impact varies but they are essential because a plant cannot reproduce without these nutrients (either directly, or because it needs them to live).
Macro nutrients are as follows; H, C, O, N, K, Ca, Mg, P, S.
Micro nutrients are as follows; Cl, Fe, B, Mn, Zn, Cu, Ni, Mo.
They are divided in to classes as follows;
Nutrients essential for organic component of plants;
C, H, O - in all organic molecules
N - in amino acids
S - in the amino acids cysteine and methionine and therefore in proteins, hormones and coenzymes.
Nutrients that store energy or ensure structural integrity
P - in sugar phosphates, ATP, NADPH2, nucleotides, phospholipids, etc.
B - Important constitute of cell wall matrix. Involved in cell elongation and nucleic acid synthesis.
Si - Not essential. Deposited in cell walls of some plants.
Nutrients that remain in ionic form;
K - important for maintaining osmoticum, also keeps electrochemical balance. Required for the operation of many enzymes.
Na - Non Essential. Required for C4 and CAM photosynthesis. Can substitute for K in some reactions
Mg - Constituent of chlorophyll. Required for the operation of many enzymes, particularly Rubisco.
Ca - Constituent of cells walls, required for signalling cell division. Required by enzymes, metabolic regulator.
Mn - Required for photosystem II function, required by many enzymes.
Cl - Required in photosynthetic reactions.
Nutrients involved in electron transfer
Fe - constituent of proteins involved in the photosynthetic, respiratory and nitrogen fixing electron transfer.
Cu - Component of plastocyanin, cytochrome oxidases and other enzymes.
Zn - constituent of dyhydrogenase enzymes and the like.
Mo - required for N2 fixation electron transfer, nitrate reductase
Ni - required for N2 fixing bacteria, used in urease.
It's important to know if a particular element is limiting growth/deficient. Soil analysis is a poor predictor - nutrients can be in the soil but not available, or sequestered from the atmosphere instead of the soil. Plant tissue analysis is more helpful.
Plants typically have a sharp impact of a lack of nutrients, then a large area where changing the nutrient amount has no impact, and then face toxicity problems if they get too much of the nutrient.
Nutrient-growth relationships are species and specific. They also can be a factor determining plant distribution. Required for economical crop production and the prevention of eutrophication.
Inadequate supply of nutrients can lead to stunted leaves, roots or stems, necrosis or chlorosis.
Deficiency symptoms depend on the functionality of the nutrient and the ability of the plant for elemental translocation from old to new parts.
Nutrient withdrawal symptoms are determined by the mobility of the nutrient in phloem. High mobility are N, K, P, Mg, Cl. Intermediate are Zn, Cu, Mn, Mo. Low - B, Fe, Ca.
Mobile elements show their symptoms of deficiency first in old leaves because the plant can move elements it does have to its newer leaves. Immobile elements show their deficiency symptoms in the new leaves first because it can't move old and already used elements there.
Deficiency symptoms;
Nitrogen. Very common deficiency, lots of soils have poor nitrogen. Symptoms are chlorosis of old leaves, often with a purple colour. Excess N can lead to a high shoot to root ratio, and also retards the seed set.
Phosphorus. Often limited in soils, and especially in Australian soils. Symptoms are stunted growth, dark green leaves, old leaves become brown and die. Delayed maturity.
Potassium. An important osmoticum. Symptoms are chlorosis of old leaves, necrosis and in cereals a loss of stalk strength leading to grain falling over etc.
Sulphur. Australian soils can be very poor in it. Mainly found/recycled in amino acids. Deficiency causes chlorosis including veins. Mostly appears first in young leaves.
Magnesium. In chlorophyll and important for enzyme regulation. Causes interveinal chlorosis in old leaves first. Rare to be a limiting nutrient.
Calcium. Usually sufficient in soils. Usually not found in acid soils - can be treated with by using lime. Has low mobility. Deficiency causes deformities - lack of cell division.
Chlorine. Most plants absorb 10 to 100 times more chlorine than they need, so deficiency is rare. Causes growth reduction, wilting, chlorotic and nerotic spots.
Iron - Deficiency causes severe interveinal chlorosis. Occurs in young leaves first. Leaves can turn white over time.
Manganese - Deficiency causes interveinal chlorosis, necrotic lesions and disorganised thylakoid membranes.
Nutrients can be present without being available to plants.
Nutrient availability can be dependent on soil pH. Micronutrient cations such as Cu2+, Fe2+, Zn2+ and Mn2+ can have low availability in neutral and basic soils because the cations bond with OH- anions. Changing the pH can make soil anions unavailable to the plant. A better option is to use chelating agents (ligands).
Plants prefer Fe3+ to Fe2+ but Fe2+ is more soluble in water and some plants can reduce iron when it's limited. They do this by releasing reductants and/or by acidifying the soil (releasing H+ ions).
Toxicity
Plants can be tolerant of toxicity in three main ways; Avoiding the substance, isolating it in compartments or by genuine tolerance.
Toxicity is hard to decipher as toxicity in one element can create deficiencies in other substances. It's also possible that multiple elements are in toxic concentrations.
Nitrogen Fixation
Nitrogen is the 4th most abundant element in plants (after HCO). It is essential in all proteins, nucleic acids, chlorophyll, hormones etc.
Available in the soil NO3-, NH4+, proteins and amino acids. Can often be in limited supply. Organic N is used by soil bacteria. NO3- leaches from soils very easily. Although the atmosphere is 78% N, it's not available to plants, however it is available to prokaryotes (esp. bacteria).
Sources of N to soils are aerosols, rain (from UV light reactions, fires and industry releases, volcanic activity), animals (from manure and decomposing animals), decomposing plants, and soil microbes.
Nitrogen Cycle
Begins with the break down of organic N in to ammonium - NH4+. NH4+ is then broken down (nitrification) to NO3-, this process is slower in acidic soils. This is then broken down (denitrification) in anaerobic processes in to N gasses (N2, NO, N2O, NO2). Nitrogen gasses are then converted in to NH3 - Nitrogen fixation and are now available for plants to use
Nitrogen fixation typically occurs by bacteria and cynobacteria. These can either be free living or with symbiotic relationships with plants. Symbiotic relationships can occur in many plants but especially occurs in legumes. Usually occurs with root nodules on the root hairs.
Occurs as follows;
Root hairs release exudates which attract bacteria to the rhizosphere, such as sugars, amino acids, and flavenoids. Flavenoids are stable organic compounds that can be species specific and trigger gene expression in the bacteria.
Nodule forming bacteria can be free living, however the flavenoids encourage the expression of nod genes that make the bacteria form nodules.
Forming the symbiosis.
The surface of the bacteria is covered in complex polysaccharides. Nod induced bacteria produces specific extracellular polysaccharides. The nodule forming root hairs have specific lectins on their surfaces. The surfaces correspond to specific polysaccharides so that only the right bacteria can form the relationship. When the right polysaccharides meet the right lectins they bond together and the root hair curls. The bacteria then digests the root hair cell wall. The plant produces an infection thread that leads all the way to the cortex in the root. The infection thread contains the bacteria and keeps it from infecting the plant. The bacteria stay in the thread and multiple. The thread is lined with cellulose. The bacteria forms large non-motile "bacteroids" which form groups surrounded by a peribacteroid membrane. The infected root cells divide and differentiate to form the root cell.
Nodules
A meristem forms around the nodule. Vascular tissue joins the nodule and stele. The nodule grows out from the cortex.
Nitrogen is the 4th most abundant element in plants (after HCO). It is essential in all proteins, nucleic acids, chlorophyll, hormones etc.
Available in the soil NO3-, NH4+, proteins and amino acids. Can often be in limited supply. Organic N is used by soil bacteria. NO3- leaches from soils very easily. Although the atmosphere is 78% N, it's not available to plants, however it is available to prokaryotes (esp. bacteria).
Sources of N to soils are aerosols, rain (from UV light reactions, fires and industry releases, volcanic activity), animals (from manure and decomposing animals), decomposing plants, and soil microbes.
Nitrogen Cycle
Begins with the break down of organic N in to ammonium - NH4+. NH4+ is then broken down (nitrification) to NO3-, this process is slower in acidic soils. This is then broken down (denitrification) in anaerobic processes in to N gasses (N2, NO, N2O, NO2). Nitrogen gasses are then converted in to NH3 - Nitrogen fixation and are now available for plants to use
Nitrogen fixation typically occurs by bacteria and cynobacteria. These can either be free living or with symbiotic relationships with plants. Symbiotic relationships can occur in many plants but especially occurs in legumes. Usually occurs with root nodules on the root hairs.
Occurs as follows;
Root hairs release exudates which attract bacteria to the rhizosphere, such as sugars, amino acids, and flavenoids. Flavenoids are stable organic compounds that can be species specific and trigger gene expression in the bacteria.
Nodule forming bacteria can be free living, however the flavenoids encourage the expression of nod genes that make the bacteria form nodules.
Forming the symbiosis.
The surface of the bacteria is covered in complex polysaccharides. Nod induced bacteria produces specific extracellular polysaccharides. The nodule forming root hairs have specific lectins on their surfaces. The surfaces correspond to specific polysaccharides so that only the right bacteria can form the relationship. When the right polysaccharides meet the right lectins they bond together and the root hair curls. The bacteria then digests the root hair cell wall. The plant produces an infection thread that leads all the way to the cortex in the root. The infection thread contains the bacteria and keeps it from infecting the plant. The bacteria stay in the thread and multiple. The thread is lined with cellulose. The bacteria forms large non-motile "bacteroids" which form groups surrounded by a peribacteroid membrane. The infected root cells divide and differentiate to form the root cell.
Nodules
A meristem forms around the nodule. Vascular tissue joins the nodule and stele. The nodule grows out from the cortex.
Biochemistry of nitrogen fixation.
N2 + 8e- + 8H+ + 16 ADP -> 2NH3 + H2 + 16ADP +16Pi
Reaction is catalysed by nitrogenase enzyme which has two components a MoFe protein and an Fe protein. Both components are O2 sensitive so nitrogen fixation can only occur when O2 is restricted - not in normal atmospheric conditions. N2 is very stable so fixation requires lots of energy to break bonds. Much more energy is produced by aerobic respiration than by anaerobic respiration.
In the nodule host cells produce leghaemogloblin which surrounds the peribacteroid membrane and controls O2 supply - keeping it at ~10nM - which is a balance so that the nitrogenase enzyme can keep working but is high enough so that aerobic respiration is possible too.
When N2 is reduced to NH3 electrons are transferred to the N2 from ferredoxin (fd) via the Fe and MoFe proteins. Requires the reducing power of reduced ferredoxin and 16 atp. The oxidised ferredoxin now needs to be regenerated and this takes 9 atp - this is a very energetically expensive process.
N2 fixation crops are very important for agriculture. They provide important nutrition for humans and livestock, and for the soil so are important in crop rotations. Mostly found in Fabaceae family which includes legumes. In Australia Acacia is our largest genus and a nitrogen fixer. Very wide spread. N2 fixers tend to have higher quantities of N than other species, and larger amounts of important proteins like rubisco. This makes them often very important in ecosystems for providing N to other plants and animals.
N2 + 8e- + 8H+ + 16 ADP -> 2NH3 + H2 + 16ADP +16Pi
Reaction is catalysed by nitrogenase enzyme which has two components a MoFe protein and an Fe protein. Both components are O2 sensitive so nitrogen fixation can only occur when O2 is restricted - not in normal atmospheric conditions. N2 is very stable so fixation requires lots of energy to break bonds. Much more energy is produced by aerobic respiration than by anaerobic respiration.
In the nodule host cells produce leghaemogloblin which surrounds the peribacteroid membrane and controls O2 supply - keeping it at ~10nM - which is a balance so that the nitrogenase enzyme can keep working but is high enough so that aerobic respiration is possible too.
When N2 is reduced to NH3 electrons are transferred to the N2 from ferredoxin (fd) via the Fe and MoFe proteins. Requires the reducing power of reduced ferredoxin and 16 atp. The oxidised ferredoxin now needs to be regenerated and this takes 9 atp - this is a very energetically expensive process.
N2 fixation crops are very important for agriculture. They provide important nutrition for humans and livestock, and for the soil so are important in crop rotations. Mostly found in Fabaceae family which includes legumes. In Australia Acacia is our largest genus and a nitrogen fixer. Very wide spread. N2 fixers tend to have higher quantities of N than other species, and larger amounts of important proteins like rubisco. This makes them often very important in ecosystems for providing N to other plants and animals.