![]() ![]() The two fields run perpendicular to each other, with one from the base to the tip of the leaf and the other from the surface to the adaxial-abaxial boundary. ![]() Past work from this lab, led by Enrico Coen, has studied this idea of a polarity field, but the new model adds a second polarity field to simulate growth in three dimensions, Whitewoods says. “And if you move that boundary, then you can change leaf shape from being flat to being cup-shaped, like a carnivorous plant.” “Our model, specifically in relation to the leaf, is that this boundary between two different domains … makes this polarity,” Whitewoods says. Though these polarity fields don’t run on electromagnetic charges, they function in a similar way, with cells throughout the tissue orienting themselves in the fields like tiny compasses. Whitewoods and his team propose that the boundary between the two genetic regions of the adaxial and the abaxial creates polarity fields throughout the leaf to direct growth. The tropical pitcher plant Nepenthes singalana, which attracts and drowns its insect prey with a pitfall trap, formed of specialized leaves, filled with nectar. One complicating factor with this line of thinking is that cell growth and division are spread more or less evenly across the leaf, not just at this margin, meaning some signal must provide growing directions to all parts of the leaf. ![]() Previous models have focused on the specific place where the boundary between these domains meets the surface at the leaf’s edge, considering it the central spot that induces cell division and controls growth, says co-lead author Chris Whitewoods, a John Innes Centre researcher. Even though the genetic makeup might be the same across these regions, their expression (whether they’re turned “on” or “off”) differs. The two regions have different physical properties and are also marked by variations in gene expression. Many plant scientists see leaves as being broken up into two domains-the upper leaf, or adaxial, and the lower leaf, or abaxial-and have looked at this separation as the key to producing a wide variety of leaf forms. The study, published this month in Science, brings together molecular genetic analysis and computer modeling to show how gene expression directs leaves to grow. Now, a study led by researchers from the John Innes Centre in England, a plant science institution, proposes a new way of understanding the genetic steps that allow leaves to grow into their particular shapes. But the biochemical processes by which plants sculpt their many leaf patterns have remained something of a mystery to scientists. Around the globe, plants have evolved to use their leaves for many purposes: broad, flat fronds to soak up sunlight, hardy needles to withstand the elements, even intricate traps to snap up unwitting insects. ![]()
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