Understanding Plant Chemistry: Elements, Natural Compounds, and Medicinal Plant Constituents

Plant Chemistry, or phytochemistry, studies the chemical compounds that constitute plants and the processes occurring in living plant tissues. One of the simplest ways to examine the elemental chemical composition of a plant is to burn it: carbon, hydrogen, oxygen, and nitrogen evaporate, leaving ash that indicates the mineral composition of the organism.

What is Plant Chemistry (Phytochemistry)?

Phytochemistry is a branch of chemistry and biology dedicated to studying the chemical composition of plants, their active substances, and biochemical processes in living tissues. It encompasses both primary compounds essential for life (carbohydrates, proteins, lipids) and secondary metabolites—such as alkaloids, flavonoids, and essential oils—that plants produce for protection and interaction with their environment.

Definition and Subject of Phytochemistry

The subject of phytochemistry includes the composition, structure, isolation, and characterization of substances of plant origin, as well as their applications in medicine, nutrition, agriculture, and industry. The discipline's roots date back to the early 20th century, notably marked by the publication of R. W. Thatcher's classic book "The Chemistry of Plant Life" in 1921, which organized early concepts of plant physiological chemistry. Today, phytochemistry is closely related to plant physiology, biochemistry, organic chemistry of carbohydrates, protein chemistry, and physical chemistry, providing a foundation for the study of natural compounds.

Elemental Chemical Composition of Plants

The elemental chemical composition of plants is determined by burning plant mass, leaving behind a mineral residue—ash. Volatile elements such as carbon, hydrogen, oxygen, and nitrogen are released as gases during combustion, while mineral substances, which come from the soil, concentrate in the ash.

Determining Chemical Composition Through Burning

Burning is a fundamental analytical method for assessing the mineral part of a plant. The ash content varies across different plant organs and cultivation conditions. Leaves, which primarily consist of living cells, contain the most ash (see more: Photosynthesis Process in Plant Leaves), while wood, which contains almost no living cells, contains the least.

Ash Content in Different Plant Organs

Ash content visibly differs among plant organs: leaves generate the highest mineral residue, while seeds and wood produce the least. This pattern is confirmed by the data presented below.

Influence of Soil and Climate Conditions on Ash Composition

The ash content in plants depends on soil and climate conditions. The drier the climate and the more salts present in the soil, the higher the ash content, although there is no direct proportion. This means that the same plant species grown in different regions may significantly differ in mineral composition.

Chemical Composition of Ash and Mineral Elements

The chemical composition of ash and the ratio of mineral elements vary between different plant species. Common elements found in ash include P, S, K, Ca, Mg, Fe, Na, Cl, Si, and Al. The concentration of each element in plant organs fluctuates depending on the growth conditions.

Ash analysis alone does not determine whether all detected elements are essential for normal growth. To reveal which elements are truly necessary, plants are grown without soil—on aqueous solutions of various salts.

Macro and Microelements in Plant Nutrition

Mineral elements in plant nutrition are categorized into macroelements and microelements based on the required quantity. Macroelements include nitrogen (N), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), and magnesium (Mg)—required in large amounts. Microelements, necessary in very small doses, include iron (Fe), zinc (Zn), boron (B), manganese (Mn), molybdenum (Mo), copper (Cu), and others.

• Macroelements: N, P, S, K, Ca, Mg—perform structural and energetic functions, and contribute to protein and nucleic acid synthesis.
• Microelements: Fe, Zn, B, Mn, Mo, Cu—act as enzyme cofactors and participate in photosynthesis and nitrogen exchange.

Plants absorb mineral elements from the soil, carbon from the air (see more: Plant Respiratory Coefficient), and hydrogen and oxygen from water.

Water Culture Method

The water culture method involves growing plants without soil in solutions of mineral salts to precisely establish the need for specific elements. By excluding certain elements from the solution, researchers observe growth and assess its necessity.

Experiments by Wilhelm Knop

Wilhelm Knop, a German agrochemist, first applied the water culture method to study mineral nutrition in the mid-19th century. He added ash elements in the form of salts to water in the proportions found in the ash of a particular plant, supplemented with nitrogenous salts, and discovered that plants thrive on mineral salt solutions.

By excluding individual elements from the nutrient mixture and observing growth, Knop identified which elements were truly essential. It turned out that some elements found in ash aren't vital, as plants still grew without them—their presence was due to absorption from the soil. Eventually, Knop identified a mandatory set: nitrogen, phosphorus, sulfur, potassium, calcium, magnesium, and iron.

Knop's Solution and Its Composition

Knop's solution is the most commonly used nutrient mixture suitable for almost all plants grown in water cultures. The necessary elements are provided in the following amounts:

• Ca(NO₃)₂ - 1 g,
• KН₂РO₄ - 0.25 g,
• МgSO₄ - 0.25 g,
• КCl - 0.125 g,
• Fе₂Сl₆ - traces.

These salts are dissolved in 1 liter of water. Further studies of mineral nutrition in water cultures led various authors to propose different nutrient mixtures based on the seven most necessary elements.

Modern Nutrient Mixtures for Hydroponics

Modern hydroponics advances Knop's idea by using precisely balanced solutions with all macro and microelements, as well as pH and conductivity control. Unlike the simple Knop's solution, industrial mixtures include zinc, manganese, boron, copper, and molybdenum in chelated forms, enhancing availability to roots. This approach is used in greenhouse vegetable production, experimental agronomy, and plant nutrition research, and other related fields—learn more about agronomical topics in the Agronomy section.

Essential Elements for Plant Growth

Essential elements are those without which a plant cannot complete its life cycle and that cannot be replaced by other elements. The water culture method has shown that sodium, silicon, and chlorine can be omitted from solutions despite their significant presence in ash, whereas iron is indispensable, even though it appears in negligible amounts in ash.

Experiments under particularly pure conditions highlighted the role of microelements. When highly distilled water, chemically pure salts containing the seven essential elements, and ebonite or paraffin-coated containers were used, growth was stunted, and sometimes entirely inhibited. This demonstrated that plants previously obtained certain elements from glass, water, and salts.

Eventually, it was established that without the addition of salts of zinc, manganese, boron, copper, molybdenum, and others, normal plants cannot be grown. Thus, for normal growth and development, plants need mineral elements: in large quantities—N, P, S, K, Ca, and Mg (macroelements), and in small quantities—Fe, Zn, B, Mn, Mo, Cu, and others (microelements).

Signs of Element Deficiency in Tobacco Water Cultures

The signs of element deficiency are vividly displayed in water cultures of tobacco grown on a full mixture and on mixtures excluding certain elements.

Tobacco Water Cultures:

1. Without Nitrogen
2. Without Phosphorus
3. Without Potassium
4. Without Calcium
5. Without Magnesium
6. On Full Nutrient Solution
7. Without Boron
8. Without Sulfur
9. Without Manganese
10. Without Iron

The absence of nitrogen, phosphorus, and potassium most strongly affects growth, but growth retardation is also noticeable with the exclusion of other elements. These observations allow the diagnosis of specific nutrient deficiencies based on visible symptoms.

Chemical Compounds in Photosynthesis

Photosynthesis is the process by which plants convert carbon dioxide and water into carbohydrates using light energy, releasing oxygen in the process. Chlorophyll—the green pigment that absorbs light—along with carbon-fixing enzymes, play key roles. Photosynthesis supplies the primary organic compounds—simple sugars, from which more complex organic substances are built.

Carbohydrates formed in photosynthesis serve as a basis for synthesizing proteins, lipids, and secondary metabolites. Organic chemistry of carbohydrates and protein chemistry describes these transformations: glucose is converted into starch and cellulose, amino acids assemble into protein-enzymes, and excess carbon is used in synthesizing protective and signaling compounds. Thus, photosynthesis is the starting point for all chemical processes in a living plant.

Bioactive Plant Compounds and Their Applications

Bioactive plant compounds are secondary metabolites that affect living organisms and are used in medicine, nutrition, and agriculture. These include alkaloids, flavonoids, terpenes, saponins, tannins, and essential oils. Many form plant defenses against herbivores and pathogens, and humans use them as medicines, nutraceuticals, dyes, and flavorings.

Antioxidant Compounds in Plants

Antioxidant compounds in plants neutralize free radicals and protect cells from oxidative damage. Notable examples include resveratrol from grapes, curcumin from turmeric, and several polyphenols. These substances form the basis of many nutraceuticals and dietary supplements and are studied as potential preventative measures against chronic diseases.

Essential Oils and Aromatic Compounds

Essential oils are volatile mixtures of aromatic compounds (terpenes and their derivatives) that give plants their scent and possess biological activity. They are extracted from flowers, leaves, peels, and wood and used in perfumery, food industry, and aromatherapy. Many essential oils have antimicrobial and insecticidal properties, linking them to natural plant defense.

Flavonoids, Coumarins, and Their Biological Effects

Flavonoids are a large class of plant pigments and antioxidants that impact human health and animal physiology; in forage plants, excess of certain flavonoids can cause reproductive issues in livestock. Coumarin, found in sweet clover, is renowned for its anticoagulant effects: when hay spoils, it transforms into dicoumarol, causing bleeding in animals—a discovery that led to anticoagulant drug development. These examples show that a compound can be both beneficial and hazardous, depending on its dose and context.

Methods for Extracting and Characterizing Plant Compounds

The extraction and characterization of plant compounds involve extracting, separating, and identifying substances from plant materials. A typical sequence covers several stages:

• Extraction using solvents (water, alcohol, hexane) or steam distillation for essential oils;
• Separation using chromatography methods (thin layer, gas, high-performance liquid chromatography);
• Characterization of structure through mass spectrometry and nuclear magnetic resonance;
• Quantitative analysis to assess the content of the target compound.

These methods underlie the analysis of natural products and are employed in research and analytical laboratories. Research on non-wood forest products, such as work by chemist K.B. Rameshkumar, demonstrates how precise characterization of compositions expands the economic use of wild species.

Practical Applications of Plant Chemistry

Plant chemistry finds applications in energy, plant protection, medicine, and nutrition. Knowledge of plant compound composition and properties enables the production of biofuel, natural pesticides, medicines, and nutritional supplements, replacing or complementing synthetic products with more sustainable solutions.

Biofuel from Plant Raw Materials

Biofuel from plant materials is produced from oils, sugars, and lignocellulosic biomass. Oilseed plants, such as jatropha (Jatropha curcas), provide non-food oil for biodiesel, while sugars and cellulose form the basis for bioethanol. Lignin—a strong polymer of cell walls—hampers biomass processing, so its content and structure affect fuel production efficiency.

Biopesticides and Natural Insecticides

Biopesticides and natural insecticides are plant protection products based on natural compounds. Azadirachtin from neem (Azadirachta indica) is a classic example, disrupting the feeding and development of insects. Such products are less toxic to the environment and rely on natural plant defense mechanisms against herbivores and pathogens.

Medicinal Compounds of Plant Origin

Many essential medicines are derived from plants. Quinine from the bark of the cinchona tree (Cinchona officinalis) is used against malaria, artemisinin from annual wormwood (Artemisia annua) is a modern antimalarial drug, and paclitaxel (Taxol) from the Pacific yew tree (Taxus brevifolia) is used in cancer treatment. The National Cancer Institute actively researches plant-derived anticancer agents.

Plant alkaloids illustrate the dual nature of phytochemistry: some serve as medications, while others are poisonous. Cannabis (Cannabis sativa) contains cannabidiol (CBD) and tetrahydrocannabinol (THC), whereas forage grasses like tall fescue and perennial ryegrass have endophytic fungi producing toxic alkaloids ergovaline and lolitrem B, harmful to livestock. The regulation of medicinal and food substances of plant origin is handled by organizations like the FDA in certain countries.

Antiquality Factors in Forage Plants

Antiquality factors are plant properties that lower their nutritional value or cause poisoning in animals. These are divided into physical (such as lignin and woodiness reducing digestibility) and chemical (toxic and palatability-reducing compounds). Forage quality depends on the plant's maturity stage: as it ages, lignin content increases and digestibility decreases.

• Tannins reduce palatability and bind proteins in feed;
• Saponins increase the risk of bloating in ruminants;
• Nitrates cause nitrate poisoning in livestock;
• Endophytic alkaloids (ergovaline, lolitrem B) lead to intoxication;
• Lignin as a physical factor limits fiber digestion.

Career and Education in Plant Chemistry

Education in plant chemistry prepares specialists for analytical laboratories, pharmaceuticals, biotechnology, and the emerging cannabis economy. The Medicinal Plant Chemistry Program at Northern Michigan University offers a unique four-year structure with bioanalytical and entrepreneurial tracks, based on chemistry and biology, laboratory standards, and a year-long capstone project. Graduates, such as Sabrina Mata, find positions in analytical laboratories, dispensaries, and cannabis marketing.

Career and educational paths in phytochemistry include several directions:

• Foundation courses in organic chemistry, biochemistry, physical chemistry, and plant physiology;
• Bioanalytical track with advanced chemistry and biology, emphasizing laboratory analytics;
• Entrepreneurial track with business and accounting for starting personal ventures;
• Internships and partnerships with employers like Abbott Laboratories, Johnson & Johnson, Ginkgo Bioworks, Green Thumb Industries, and Cambium Analytica laboratory;
• Graduate studies leading to research careers, including at institutions like Purdue University and the University of Minnesota.

The issue of sustainable development and natural resources brings phytochemistry into synergy with programs like Stanford's Doerr School of Sustainability at Stanford University. For researchers, disseminating findings is increasingly important: raising awareness, targeting audiences, engaging stakeholders, and translating scientific knowledge into practice. Effective communication—from publications in Nature and Springer Nature to educational videos on YouTube—enhances the impact of research on sustainable development and plant chemistry. Related practical materials can be found in sections Medicine and Agronomy.