Creating these graft chimeras was time-consuming and involved an element of chance; often the growing tip of the chimeral shoots reverted back to a non-chimeral shoot rendering the leaves generated from that point on useless for analysis. However, over the past decade enough leaves were recovered that were perfectly bisected, homogeneous on one side of the midvein and with a unique epidermis on the other. This allowed Marcotrigiano to use them to examine how leaf cell layer affects leaf size and shape.
Marcotrigiano's most striking finding was the important role that the epidermal cells played in determining leaf size. He found that leaves grew asymmetrically when one side of the midvein contained identical cell layer arrangements and the other side contained epidermal cells that differed genetically from the mesophyll cells. When big-leaf epidermal cells surrounded small-leaf mesophyll cells in an otherwise all small-genotype leaf, the big-leaf epidermal cells caused that side of the leaf to be bigger than the other side. In contrast, when small-leaf epidermal cells surrounded big-leaf mesophyll cells in an otherwise all big-genotype leaf, the small-leaf epidermal cells caused that side to be smaller than the other side.
Epidermal cells not only controlled overall leaf size, but also influenced the number of cells produced in the mesophyll layer. For example, small-leaf epidermal cells surrounding big-leaf mesophyll cells caused the mesophyll cells to have many fewer cell divisions than when they were surrounded by big-leaf epidermal cells. Interestingly, the epidermal cells did not influence, or change, the size of the mesophyll cells.
Marcotrigiano concludes that while regulation of leaf size is complex and influenced by many factors and many genes, his findings show that communication b
|Contact: Richard Hund|
American Journal of Botany