Immunogold labelling of a sieve element (SE) in mature stem with TLP1 antiserum. A) Low magnification image of sieve element. Scale bar = 5 μm. Arrows indicate position of sieve plate and cell wall that was enlarged in panels B and C, respectively. CA, callose; CW, cell wall; S, starch; SP, sieve pore. Scale bars = 500 nm.