BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

IV. PLANT ANATOMY AND MORPHOLOGY

Primary Organic Substances

CARBOHYDRATES. Carbohydrates account for 1–2% to 85–90% of the dry matter comprising a plant Organism or its individual Organs. They serve as the primary nutrient and structural material for plant Cells, Tissues, and organs. Carbohydrate molecules consist of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. Structurally, they are divided into Monosaccharides (or monoses) and Polysaccharides (or polyoses). The latter are subdivided into Primary and secondary polysaccharides.

Primary polysaccharides include Disaccharides (sucrose, maltose, cellobiose), trisaccharides (raffinose), and tetrasaccharides (stachyose).

Secondary polysaccharides are complex, high-molecular-weight polymer compounds. These include mucilages, starch, Glycogen, inulin, Cellulose, hemicellulose, pectic substances, Agar-agar, and others.

Monosaccharides are derivatives of polyhydric alcohols. Based on the number of carbon atoms in their molecules, they are classified into trioses – С₃Н₆О₃ (glyceraldehyde and dihydroxyacetone), tetroses – С₄Н₈О₄ (erythrose), pentoses – С₅Н₁О₅ (xylose, arabinose, ribulose, ribose), hexoses – С₆Н₁₂О₆ (glucose, fructose, galactose, mannose), and heptoses – С₇Н₁₄О₇ (monoheptulose, sedoheptulose).

Glucose, or grape sugar, occurs in a free state in the green parts of plants, seeds, fruits, and honey. It is a building block of starch, cellulose, hemicellulose, glycogen, dextrins, sucrose, maltose, raffinose, and numerous Glycosides.

Fructose, or fruit sugar, is found in the green parts of plants, floral nectar, and fruits, and is a component of honey. Along with glucose, it forms sucrose and the high-molecular-weight polysaccharide inulin, which accumulates in large quantities in plants of the Asteraceae family, particularly in the roots of elecampane and chicory, and the tubers of Jerusalem artichoke.

Galactose is a structural component of disaccharide molecules such as lactose (milk sugar), melibiose, the trisaccharide raffinose, and high-molecular-weight polysaccharides like agar-agar, hemicellulose, and mucilage. In its free state, it crystallizes on ivy fruits.

Mannose in plants occurs as part of high-molecular-weight polysaccharides, specifically mucilage and hemicellulose. Mannose is obtained through the acid Hydrolysis of nutshell hemicellulose.

Sorbose is formed during the bacterial Fermentation of rowan berry juice and serves as an important intermediate in the synthesis of Vitamin C (ascorbic acid).

Arabinose belongs to the pentoses. It occurs in plants as a component of mucilage, plant Gums (mucilages), pectic substances, and hemicelluloses. Arabinose is obtained via acid hydrolysis of cherry gum or beet pulp.

Xylose (wood sugar) is a component of plant mucilage, gums, and hemicelluloses. It is produced through the acid hydrolysis of bran, straw, wood, and corn cobs.

Ribulose is the primary CO₂ acceptor during Photosynthesis.

Ribose and deoxyribose are Components of nucleic acids, while the ribose derivative ribitol is part of certain Vitamins and Enzymes.

Sorbitol (С₆Н₁₂О₆) is a hexahydric alcohol found in the fruits of rowan, plum, peach, apple, pear, cherry, and apricot. Depending on the oxidation conditions, it can yield glucose, fructose, or sorbose. It serves as a sugar substitute for individuals with Diabetes Mellitus.

Mannitol is a hexahydric alcohol secreted On the surface of ash bark, and is also present in carrot roots, onions, olives, pineapples, and mushrooms; it is most abundant in brown Algae of the Laminariaceae family. Oxidation of mannitol yields mannose or fructose.

Disaccharides consist of residues of two monosaccharide molecules. The most important disaccharides are sucrose, lactose, maltose, trehalose, gentiobiose, and cellobiose.

Sucrose (С₁₂Н₂₂О₁₁), commonly known as cane sugar or beet sugar, is found in leaves, stems, roots, tubers, seeds, and fruits. Its hydrolysis yields a mixture of glucose and fructose.

Lactose, or milk sugar (С₁₂Н₂₂О₁₁), is found in milk and the pollen tubes of certain plants. Hydrolysis of lactose yields galactose and glucose.

Maltose, or malt sugar (С₁₂Н₂₂О₁₁), is formed during the enzymatic Hydrolysis of Starch by diastase (amylase). The enzyme maltase breaks down maltose into two glucose molecules.

Trehalose, or mushroom sugar (С₁₂Н₂₂О₁₁), is found in Fungi, Yeasts, and the sclerotia of Claviceps (ergot). Its hydrolysis yields two glucose molecules.

Gentiobiose (С₁₂Н₂₂О₁₁) is a disaccharide containing two glucose molecules. It is a component of many glycosides, notably amygdalin and crocin. In a bound state, gentiobiose is found in gentian roots.

Cellobiose (С₁₂Н₂₂О₁₁) is the primary structural unit of cellulose. In a free state, it occurs in the sap of certain trees. It breaks down into two glucose molecules.

Trisaccharides are represented by raffinose (С₁₈Н₃₂О₁₆). It is found in sugar beet roots, molasses, and cottonseed. The hydrolysis of raffinose yields glucose, fructose, and galactose.

Tetrasaccharides include stachyose (С₂₄Н₄₂О₂₁), which is found in the roots of lamb's ear (stachys), the seeds of yellow lupine, soybeans, peas, lentils, and chickpeas. It breaks down into two galactose molecules, glucose, and fructose.

Polysaccharides are widely distributed among carbohydrates. They include starch (С₆Н₁₀О₅), among others. Within cells, it occurs as granules that vary in properties and chemical composition depending on the plant part and, particularly, on the plant species. Starch grains have a concentric or eccentric shape and a simple, compound, or semi-compound Structure. Starch is insoluble in Water, only Swelling in it. Starch consists of 96–98% polysaccharides, which yield glucose upon acid hydrolysis; 0.2–0.7% Mineral Substances, primarily phosphoric acid; and 0.6% high-molecular-weight Fatty acids (palmitic, stearic, and others). The carbohydrate portion of starch is composed of two polysaccharides: amylose and amylopectin. During the Enzymatic hydrolysis of starch, dextrins are formed first; these differ very little from starch in molecular size and properties. Further breakdown converts them into maltose and then glucose. Starch and dextrins support Cholesterol METABOLISM and improve Digestion. Their colloidal solutions serve as the base for many medicinal mixtures.

Inulin is a high-molecular-weight, water-soluble storage polysaccharide. It is found in large quantities in the tubers of Jerusalem artichokes and dahlias, as well as in the roots of dandelions and chicory. The enzyme inulinase, present in Yeast and certain plants, breaks down inulin to produce fructose.

Glycogen is a storage polysaccharide found in animal and human tissues, fungi, and sweet corn kernels. It yields glucose upon acid hydrolysis. Structurally, glycogen resembles amylopectin, but it differs in having a higher molecular weight.

Lichenin is a storage polysaccharide of Lichens, where its content can reach up to 50% of the dry weight. Upon hydrolysis, it breaks down into glucose.

Cellulose is a structural polysaccharide that serves as the main constituent of Plant Cell Walls. Cellulose is insoluble in water, only swelling in it. Hydrolysis first yields the disaccharide cellobiose, which then breaks down into two glucose molecules. Cellulose molecules contain 1,400–10,000 glucose residues. Unlike the branched polymers of glucose (starch and glycogen), cellulose has a thread-like, unbranched molecular structure. Through Hydrogen Bonds, 50–100 cellulose molecules combine to form micelles, which in turn assemble into microfibril fibers. Cellulose is not digested in the human gastrointestinal tract. It is digested by ruminants, whose stomachs harbor microorganisms that hydrolyze cellulose using their specific cellulase enzyme. Cellulose stimulates intestinal peristalsis, AIDS in cholesterol excretion, positively affects Blood pressure and Liver metabolic processes, and participates in the synthesis of B-group vitamins.

Hemicelluloses are a group of high-molecular-weight polysaccharides that are insoluble in water but soluble in alkaline solutions. They are abundant in lignified plant tissues—wood, corn cobs, straw, seed coats, nut shells, and bran. Acid hydrolysis of hemicelluloses yields mannose, galactose, arabinose, or xylose, leading to their respective classifications: Mannans, galactans, arabans, and xylans.

Mucilages and gums are a group of colloidal, water-soluble polysaccharides that form viscous and sticky solutions. Gums can be observed as 'glue' on injured branches of cherry, apricot, and plum trees. Gums consist of galactose, mannose, arabinose, xylose, and glucuronic acid residues. Mucilage is abundant in flax and rye seeds, marshmallow roots, coltsfoot leaves, and others. It is composed of xylose, arabinose, and galactose residues. Mucilaginous substances are used to treat inflammations of the Upper Respiratory Tract and the digestive canal because they promote the epithelialization of damaged mucous membranes.

Pectic substances are high-molecular-weight carbohydrate compounds that form part of plant cell walls. They are particularly abundant in the pericarp of juicy fruits, tubers, ROOT vegetables, and plant stems. In plants, pectic substances exist in two forms: insoluble protopectin and soluble pectin. For instance, during The Development of apples, pears, and plums, protopectin is deposited in The Cell walls; as the fruits ripen, it is converted into pectin through the action of the enzyme protopectinase. In plants, pectic substances (protopectin) within the middle lamellae cement adjacent cell walls and cells together.

During the hydrolysis of pectic substances, maceration occurs—the Separation of plant cells within plant tissues due to The breakdown of intercellular substance. Soluble pectin is a polysaccharide built from galacturonic acid residues. In the presence of acid (pH 3.1–3.5) and sugar (65–70%), pectin forms a gel used in confectionery manufacturing. In the intestines, Pectins can adsorb and remove toxic substances, radionuclides, and heavy metal salts from the body, as well as enhance digestion. Pectin reduces blood cholesterol levels.

Agar-agar is a high-molecular-weight polysaccharide found in The Cell wall matrix of red algae. It is insoluble in cold water, but dissolves readily upon heating, turning into a gel upon cooling. Agar-agar is a polymer composed predominantly of galactose. It is used to prepare nutrient media for laboratory cultures of Bacteria, fungi, algae, spores, and plant pollen, as well as in medicine and the confectionery and food industries.

Alginic acid, a cell wall polysaccharide of brown algae, is an analogue of pectic acids. It consists of mannuronic acid residues. In algae, alginic acid occurs in the form of salts and accounts for 30% of their dry weight. Sodium alginate is an effective emulsifier and is therefore used as a stabilizer in The production of ice cream, fabric Dyes, and industrial emulsions.

Chitin is a polymer composed of several hundred acetylglucosamine residues. It is insoluble in water and organic Solvents. It is hydrolyzed by concentrated Hydrochloric acid. Chitin forms the microfibrils in the fungal cell wall. Fungi contain the enzyme chitinase, which breaks down chitin into glucosamine.