PLANT BIOPHYSICS - Y. I. Posudin - 2004

II. TRANSPORT PROCESSES IN THE SOIL-PLANT-ATMOSPHERE SYSTEM

12. EFFECT OF ENVIRONMENTAL FACTORS ON PLANTS

12.3. EFFECT OF TEMPERATURE ON PLANTS

Thermoperiodism. The dependence of plant growth on daily Temperature fluctuations is called thermoperiodism. Plant growth processes depend on the geographical zone they inhabit and are determined by characteristic temperatures [Musiyenko, 2001]: the minimum temperature, at which plant growth begins; the optimum temperature, which is most favorable for growth; and the maximum temperature, at which growth ceases. For thermophilic plants, the minimum temperature exceeds 10 °С, while the optimum ranges between 30-40 °С; for cold-resistant plants, the minimum temperature ranges between 0-5 °С, and the optimum is within 25-31 °С. The maximum temperature for most plants lies in the interval of 35-45 °С.

Effect of temperature on Photosynthesis. Different plant species exhibit a temperature dependence of photosynthetic activity; the maximum of this dependence lies in the region of 20-30 °С, although inhabitants of hotter regions are characterized by a higher optimum range. In addition, plants possess The ability to acclimate to specific temperature regimes. At high temperatures, the shape of the curve representing the dependence of plant photosynthetic activity on temperature is determined by the duration of the temperature factor that causes inactivation of the photosynthetic system. However, the inactivation temperature depends on the plant species: for instance, it is 42 °С for Atriplex sabulosa (a native of cold coastal zones) and 50 °С for Tidestromia oblongifolia (a desert plant). It is believed that such processes as photosystem PSI Electron Transport and NADP-reductase activity are practically independent of short-term exposures to high temperatures. At the same time, membrane permeability, dark Respiration, and carboxylase activity are sensitive to high temperatures.

Vernalization. Seasonal temperature changes are the primary factor influencing plant flowering (especially in cereals). For example, winter cereals require exposure to low temperatures (from -1 to +10 °С) for several months. The process of flowering induction under METABOLISM/18.html">The Influence of lowered temperatures is called vernalization (from Latin vernalis - spring). Perennial plants (such as fruit trees) also require annual exposure to low temperatures in order to flower. Seeds are kept at low temperatures for a long time prior to germination; this process is called stratification. The effectiveness of stratification increases if the seeds are moist.

Dormancy and leaf fall. Exposure to low temperatures or photoperiod can trigger The Emergence of plants or seeds from dormancy, a state characterized by the cessation of growth of the plant (or its Organs) and seeds. Temperature also plays a crucial role in leaf abscission.

High-temperature stress. The most common PLANT RESPONSE TO high temperatures is the synthesis of heat Shock Proteins (HSPs), which are specific Polypeptides normally absent in plants. Although the Functions of HSPs are not yet fully understood, it is believed that their synthesis is associated with the induction of plant thermotolerance in response to short-term high-temperature stress. High temperatures cause cellular and tissue destruction, accompanied by a loss of membrane integrity and consequent ion leakage. It is worth noting the ability of many plants to adapt to high temperatures.

Low-temperature stress. There are two types of damage caused to plants by low temperatures. The first type is characteristic of tropical or subtropical plants (such as rice, legumes, corn, and tomatoes): low temperatures (below 10 °С) cause wilting or growth arrest, inhibition of reproductive functions, and even the death of the entire plant. If the low-temperature exposure is brief, the plant may recover. The second type of damage is caused by the freezing of Water within plant Tissues. In many plants, tissues can be killed at temperatures ranging from -1 to -3 °С. The Mechanism of low-temperature action during chilling is associated with the disruption of Cell membranes, whose permeability changes, resulting in the leakage of the intracellular medium. During freezing, ice crystals form inside The Cell, leading to the mechanical destruction of membranes. Furthermore, since ice has a lower chemical potential than water, the freezing of the extracellular medium draws water out of the cell, leading to its subsequent dehydration.