Leaf expansion is a process by which plants make efficient use of the space around them by causing their leaves to enlarge, or wither. This process enables a plant to maximize its own biomass, whether it be due to increased surface area; which enables more sunlight to be absorbed by

chloroplasts A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

, driving the rate of

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

upward, or it enables more stomata to be created on the leaf surface, allowing the plant to increase its

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

intake.

Mechanism

Initially, sensory organs, such as chloroplasts, the

cambium A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from w ...

, and

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the su ...

s, detect an external stimuli, such as light. The stimulus triggers biochemical events downstream that result in the expansion of tissue in the leaf. There are two processes found by which this occurs: osmotic regulation, which has a temporary effect that causes leaves to increase size, or wall extensibility, which gradually changes the leaf over time and permanently enlarges it.

Osmotic regulation

Red light hits leaves and depolarizes the plasma membrane of

plant cells Plant cells are the cells present in green plants, photosynthetic eukaryotes of the kingdom Plantae. Their distinctive features include primary cell walls containing cellulose, hemicelluloses and pectin, the presence of plastids with the capa ...

via

photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicit ...

calcium and chloride ion channels. Chloride leaves the cells, while calcium enters. This depolarization causes an osmotic shift in ionic concentrations in the

apoplast Inside a plant, the apoplast can mean the space outside of cell membranes, where material can diffuse freely; that is, the extracellular spaces. ''Apoplast '' can also refer especially to the continuum of cell walls of adjacent cells; fluid and ...

, which concurrently causes an increase in

turgor pressure Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibriu ...

based on apoplastic solute potentials, forming an electrical gradient across the plasma membrane. The increase in turgor pressure causes the cells to expand, enabling the chloroplasts to shift to a different area, and the collective expansion of all the cells at once causes the leaf itself to become larger and more rigid. The movement of the chloroplasts enables light that was previously unobtainable to be reached and utilized.

Wall extensibility

Blue light hits a plant's leaves and causes the downstream activation of

proton pumps A proton pump is an integral membrane protein pump that builds up a proton gradient across a biological membrane. Proton pumps catalyze the following reaction: : n one side of a biological membrane/sub> + energy n the other side of the membr ...

. In turn, this results in a decrease of the cell wall's pH. The decrease, in conjunction with membrane-bound proteins called expansins, increases the plasticity of the apoplastic membrane. This plasticity enables more cell area to be created during

cell division Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there ar ...

, which expands the leaf as more standard-sized cells are added. The increase in overall

organelles In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' th ...

and cell area cause more stomates to form and more light to be utilized.

In nature

Different types of plants tend to grow at different rates. Those that grow slowly tend to prioritize having much smaller leaf areas in order to conserve energy, and will only expend them when an excess of light is close by. This is due to light being scarce, their slow growth preventing them from reaching the heights that fast-growing plants reach that provides them with plentiful amounts of light. As a contrast, the fast-growing plants have large leaves as a result of constantly being bathed in light. The differing leaf sizes allow both types of plants to coexist in nature while in different ecological niches, and explains why certain canopy layers tend to be highly uneven.

References

{{reflist * * * * Plant physiology Botany

Mechanism

Osmotic regulation

Wall extensibility

In nature

See also

References