How Do Grass Leaves Roll Up During Drought?
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How do grass leaves roll up during drought? The short answer is that the leaf changes shape because of pressure inside a specific group of cells. The first source describes the response as “reversible leaf rolling along the longitudinal leaf axis upon water limitation or heat stress conditions.” The cells at the centre of this response are bulliform cells, and the mechanism depends on how much water they hold. This article explains that mechanism, using two PMC sources, and it notes where the sources stop.
Quick answer
- The cells that drive rolling are large epidermal cells. The second source describes them as “huge epidermal cells occurring in fan-shaped groups” on the upper leaf side.
- Rolling follows turgor pressure. The second source states that “The leaf rolls in, when the turgor pressure in the bulliform cells is low.”
- Rolling reduces water loss. The first source says that “Leaf rolling prevents water loss, photosynthetic loss, and increases drought resistance in numerous species of the Poaceae.”
- The leaf can open again. According to the second source, “It unrolls again, when the bulliform cells are turgescent.”
What drives the roll
Bulliform cells are the central cell type in this response. The first source defines them as “enlarged, colorless cells located in the epidermis,” and it notes that in maize they are arranged in strips along the leaf. The source adds that bulliform cells “have been implicated in the leaf rolling response.” That is an association supported by the research, not a complete account of every grass.
The second source places the cells in a broader context. It states that “Various functions are attributed to them, such as water storage.” Water storage is one of several functions the source lists. The same source focuses on “the hydraulically driven movements of grasses by bulliform cells,” which is the mechanical side of the story.
The cells are not always spread the same way. The second source describes both arrangements, noting that “Bulliform cells are distributed along the entire leaf” in one case and that “Bulliform cells are concentrated near the midrib” in the other. Those two arrangements are what the source links to rolling and to folding respectively.
Turgor pressure as the switch
Plant cells can hold pressure because of their walls. The second source explains that plant cells differ from animal cells “because of the existence of a stiff cell wall around their cell membrane, which allows plant cells to sustain an internal hydrostatic pressure.” This internal pressure is called turgor. The source describes turgor as “generated by an osmotic gradient caused by the semipermeable cell membrane,” which “allows the osmotic flow of water into the cell vacuole.”
The same source connects this pressure to plant movement in general: “The basis for most reversible plant movements are changes in turgor at the cell level.” The source also notes that “These small changes can aggregate to a macroscopic shape change at the tissue level and finally at the organ level.”
In the drought case, the switch is simple to state. When the bulliform cells lose pressure, the leaf rolls. When they regain pressure, the leaf unrolls. The second source supports both directions with its figure description: the leaf “rolls in, when the turgor pressure in the bulliform cells is low,” and it “unrolls again, when the bulliform cells are turgescent.”
Shrinkage under dehydration
The first source provides a measurement of the shrinkage that leads to rolling. It states that a new imaging method was used “to demonstrate differential shrinkage, upon leaf dehydration, of BCs relative to other epidermal cells.” In other words, the bulliform cells shrink more than their neighbours when the leaf dries. The figure caption adds that “Bulliform cells show increased shrinkage upon dehydration.”
The source ties this measurement to its central question. Its stated aim was to “examine the role of BCs in the adult maize leaf rolling response to dehydration,” which is the question this section answers.
The cuticle and water loss
Rolling is one way a leaf limits water loss. The cuticle is the other. The first source describes the cuticle as “the first layer of protection of aerial plant tissue and represents an important interaction surface with the environment.” It also notes that “Retaining water in the epidermis and the underlying plant tissue to limit dehydration is one of the most important roles of the plant cuticle.”
The source explains where the water barrier comes from: “waxes, rather than cutin, provide the majority of the water barrier property of the cuticle.” The first source’s title names the bulliform cell cuticle directly, so its cuticle analysis is aimed at the same cells that drive rolling.
For a related look at the leaf surface, the article on how a leaf cuticle reduces water loss covers the cuticle side in more detail. The two mechanisms are different, and it helps to read them side by side. A second related read is how cacti survive drought, which covers a different drought response.
Variation across grass species and lines
The first source reports scoring across a broad set of maize lines. It states that “Leaf rolling was scored on a set of 468 maize inbred lines from the Wisconsin Diversity panel.” Scoring many lines allows the source to compare them, which is a different angle from the mechanism itself.
The second source studied a different grass, and it describes its approach: “Functional morphological investigations were carried out on the selected model plant Sesleria nitida.” The two sources therefore cover two grasses. Together they show the same mechanism in different plants, but they do not cover every grass species.
The second source also used modelling to check the mechanism. It notes that a finite-element analysis “was conducted to improve comprehension of the role of bulliform cells in leaf involution.”
How we chose
Both sources are PMC articles that opened directly with HTTP 200 on the check date. The first has the title “Structure-function analysis of the maize bulliform cell cuticle and its potential role in dehydration and leaf rolling,” which matches the drought question. The second has the title “Learning from plant movements triggered by bulliform cells: the biomimetic cellular actuator,” which covers the grass movement mechanism. Neither is a retail page, and each was read as text before any statement was drawn from it.
What we could not verify
The sources describe the mechanism well, but they do not cover every grass or every drought. The first source says that “Only limited research is available on cuticle composition and function in adult maize leaves,” so the cuticle part of the story rests on a narrow base.
What the sources do not say
The sources do not give a general rule for all grasses. The first source notes that “Little is known about variation in cuticle composition and structure on specific epidermal cell types.” That gap means the exact wax chemistry of bulliform cells in other species is not settled by these two papers. The second source focuses on one model grass and on “the hydraulically driven movements of grasses by bulliform cells,” so its findings are a model for the mechanism, not a survey of all grasses.
Frequently asked questions
Why do grass leaves roll up when it is dry?
The first source describes rolling as a response to “water limitation or heat stress conditions.” The second source explains the mechanism: “The leaf rolls in, when the turgor pressure in the bulliform cells is low.”
Do all grasses roll their leaves?
The first source says that leaf rolling “increases drought resistance in numerous species of the Poaceae,” which is the grass family. The phrase names numerous species, not all grasses, so the sources do not settle the question for every species.
Does the leaf unroll after it gets water?
Yes, according to the second source. It states that the leaf “unrolls again, when the bulliform cells are turgescent,” which describes the return to a flatter shape once the cells regain pressure.
Is leaf rolling only a drought response?
The first source describes it as a response to “water limitation or heat stress conditions,” so heat is also named. The sources focus on water loss, as the quote on drought resistance shows.
Can the rolling mechanism inspire engineering designs?
The second source has that goal. Its title describes it as “the biomimetic cellular actuator,” and it states that “The kinetic amplification of the leaf halves is based on the interaction of turgor-dependent bulliform cells.”
Sources
- “Structure-function analysis of the maize bulliform cell cuticle and its potential role in dehydration and leaf rolling.” https://pmc.ncbi.nlm.nih.gov/articles/PMC7598327/ (HTTP 200, opened 2026-10-28)
- “Learning from plant movements triggered by bulliform cells: the biomimetic cellular actuator.” https://pmc.ncbi.nlm.nih.gov/articles/PMC7482577/ (HTTP 200, opened 2026-10-28)
