Life scientists from UCLA's
College of Letters and Science hv discovered fundamental rules of leaf design that underlie plants' ability to produce leaves that vary
enormously in size. In their mathematical design, leaves are the "perfect machines," said Lawren Sack, a professor of ecology & evolutionary biology & senior author of the research.

The UCLA team discovered the mathematical relationships using "allometric analysis," which looks at how the proportions of parts of an organism change with differences in total size. This approach has been used by scientists since GALILEO but had never b4 been applied to the interior of leaves.

Reporting in the October issue of an American Journal of Botany, the biologists focused on how leaf anatomy varies across leaves of different sizes. They examined plant species from around the world, all grown on the UCLA campus. While it is easy to observe major differences in leaf surface area among species, they said, differences in leaf thickness are less obvious but equally important. Grace John, a UCLA doctoral student in ecology & evolutionary biology & lead author of the research says:"Once you start rubbing leaves between your fingers, you can feel that some leaves are floppy and thin, while others are rigid & thick," "We started with the simplest questions -- but ones that had never been answered clearly -- such as whether leaves that
are thicker or larger in area are constructed of different sizes or types of cells."

WHAT THEY DID:
The researchers embedded pieces of leaf in plastic & cut cross-sections thinner than a single cell to observe each leaf's microscopic layout. This allowed them to test the underlying relationship betwn cell & tissue dimensions & leaf size across species.Leaves are made up of three basic tissues, each containing cells with particular functions: the outer layer, or EPIDERMIS; the MESOPHYLL, which contains cells that conduct photosynthesis; & the VASCULAR TISSUES, whose cells are involved in water & sugar transport.

THEN:
The team found that the thicker the leaf, the larger the size of the cells in all of its tissues -- except in the vascular tissue.

:
These relationships also applied to the components of the individual cells. Plant cells, unlike animal cells, are surrounded by carbohydrate-based cell walls, & the scientists discovered that the larger cells of thicker leaves are surrounded by thicker cell walls, in a strict proportionality. The team was surprised by the "extraordinary" strength of the relationships linking cell size, cell-wall thickness and leaf thickness across diverse and distantly related plant species. These relationships can be described by new, simple mathematical equations, effectively allowing scientists to predict the dimension of cells & cell walls based on the thickness of a leaf. In most cases, the relationships the team found were what is known as "isometric." This means that if a leaf has a larger cell in one tissue, it has a larger cell in another tissue, in direct proportion, as if you blew up the leaf & all its cells using Photoshop.

By contrast, a leaf's area is unrelated to the sizes of the cells inside. This allows plants to produce leaves with a huge range of surface areas without the need for larger cells, which would be inefficient in function, the researchers said. The team hypothesized that these strong mathematical relationships arise frm leaf devt -- the process by which leaves form on the branch, growing from a few cells that divide into many, with cells then expanding until the leaf is fully mature. because light can penetrate only so many layers of cells, leaves
cannot vary much in the number of cells arranged vertically. The expansion of individual cells and their cell walls occurs simultaneously & is reflected in the thickness of the whole leaf. On the other hand, the number of cells arranged horizontally in the leaf continues to increase as leaves expand, regardless of the size of the individual cells. The new ability to predict the internal anatomy of leaves from their thickness can give clues to the function of the leaf, because leaf thickness affects both the overall photosynthetic rate & the lifespan- "A minor difference in thickness tells us more about the layout inside the leaf than a much more dramatic difference in leaf area". The design of the leaf provides insights into how larger structures can be constructed without losing function or stability.

The new allometric equations are an important step 2ward understanding the design of leaves on a cellular basis. And because leaves are so diverse, there is much to learn! In future research, the group will study species that are very closely related in an effort to uncover any evolutionary relationships betwn leaf design & function. John says: "What makes the cross-sections especially exciting is the huge variation frm one species to the next, some hv relatively enormous cells in certain tissues, & cell shapes vary frm cylindrical to star-shaped. Each species is beautiful in its distinctiveness. All of this variation needs decoding."

Culled frm: #ScienceDaily

Fundamental & quantitative discoveries lyk dz prove how exciting science can b, thr r so many properties of leaves scientists can't yet imitate synthetically. Jst like John said; "Leaves are providing us with the blueprints for bigger, better things. We just have to look close enough to read them." Evry part of me wishes findings lyk dz cld b made in Nigeria, all we do is cram! even up to PhD level. Thr aint much hlp cumin though.

The image: Transverse cross-section of a very thin
sunflower leaf (Helianthus annuus) to a thick tea leaf (Camellia sasquana). Along with total leaf thickness and leaf area, the leaves differ dramatically in cell size and in the thickness of cell walls according to specific mathematical.equations newly discovered by the UCLA.research team.

Here I am


BEHOLD A LEAF