Plant Physiology Glossary

A plant hormone involved in stress responses, promoting stomatal closure during drought and maintaining seed dormancy until conditions favor germination.

A region of actively dividing, undifferentiated cells at the tips of roots and shoots that is responsible for primary (lengthwise) growth of the plant.

A class of plant growth hormones, primarily indole-3-acetic acid (IAA), that regulate cell elongation, apical dominance, tropisms, and root development.

A photosynthetic pathway that spatially separates initial CO2 fixation (in mesophyll cells) from the Calvin cycle (in bundle sheath cells), concentrating CO2 to reduce photorespiration.

The light-independent reactions of photosynthesis in the chloroplast stroma where CO2 is fixed by RuBisCO and reduced to glyceraldehyde-3-phosphate (G3P) using ATP and NADPH.

A waxy band of suberin in the cell walls of root endodermal cells that blocks apoplastic water movement and forces selective uptake of minerals through the symplastic pathway.

A green pigment located in the thylakoid membranes of chloroplasts that absorbs light energy (primarily red and blue wavelengths) for photosynthesis.

A double-membrane organelle in plant cells containing chlorophyll where photosynthesis occurs. It has internal thylakoid membranes and a fluid-filled stroma.

A plant hormone class that promotes cell division, delays leaf senescence, and stimulates shoot development, often working antagonistically with auxin.

A gaseous plant hormone that regulates fruit ripening, flower and leaf senescence, abscission, and the stress response known as the triple response.

A class of plant hormones that promote stem elongation, seed germination, and flowering by stimulating cell division and elongation.

Directional plant growth in response to gravity, with roots typically growing downward (positive) and shoots growing upward (negative), sensed by statoliths.

The biological conversion of atmospheric nitrogen gas (N2) into ammonia (NH3) by nitrogenase enzymes in symbiotic bacteria such as Rhizobium or free-living soil microorganisms.

Vascular tissue composed of sieve tube elements and companion cells that transports dissolved sugars and organic compounds from source to sink tissues.

The response of plants to the relative lengths of light and dark periods, which controls physiological processes such as flowering, dormancy, and tuber formation.

A metabolic pathway where RuBisCO oxygenates RuBP instead of carboxylating it, producing glycolate that requires energy to recycle, thereby reducing net photosynthetic efficiency.

The biochemical process by which plants, algae, and some bacteria convert light energy, carbon dioxide, and water into glucose and oxygen.

Directional growth of a plant organ toward or away from a unilateral light source, mediated by the redistribution of auxin to the shaded side.

A blue-green photoreceptor pigment that exists in two forms (Pr and Pfr) and mediates plant responses to red and far-red light, including germination and flowering.

Ribulose-1,5-bisphosphate carboxylase/oxygenase, the enzyme that catalyzes the first step of carbon fixation in the Calvin cycle and also initiates photorespiration.

Microscopic pores on the surface of leaves and stems, bounded by guard cells, that regulate gas exchange (CO2 in, O2 and H2O out).

The evaporative loss of water from aerial plant parts, primarily through stomata on leaf surfaces.

The pressure exerted by water inside a plant cell against the cell wall. It is essential for maintaining cell rigidity, driving cell expansion, and powering stomatal movements.

A quantitative measure of the tendency of water to move from one area to another, determined by solute concentration and physical pressure, expressed in megapascals (MPa).

Vascular tissue composed of tracheids and vessel elements that transports water and dissolved minerals upward from roots to leaves.