Does barley (Hordeum vulgare L.) pollen swell in fractions of a second?

Microscopic studies revealed that freshly collected six-rowed barley (Hordeum vulgare L. cv. Baegdong) pollen swelled in 600 50 milliseconds (ms) (0.6 +/- 0.05s) upon hydration with distilled water. The half time (T-1/2) of complete swelling of pollen was 200 ms, which gave values of 0.14 x 10(-5) ms(-1) MPa-1 for hydraulic conductivity (Lp). This value was higher than usually reported for higher plant cells. It was hypothesized that potassium (K) may be involved in creating osmotic gradient, resulting in speedy uptake of water and ultimately rapid swelling of pollen. Macallum's solution was used to stain K in pollen. It was found that K concentrated in the aperture area of pollen. However, breaking of pollen further revealed that heavy stains of K were not only found at the aperture wall of pollen but also found at the part of cytoplasmic area that attached with the aperture. Furthermore, energy dispersive X-ray analysis (EDX) verified staining results of K at the aperture area of pollen. These results demonstrate that barley pollen swell in fractions of a second. The high hydraulic conductivity of pollen membrane could be responsible for rapid movement of water through membrane. These results also suggest that there could be a possible role of K located at the aperture area, in rapid swelling of pollen by creating osmotic gradient across membrane, which is the prerequisite of rapid protrusion of pollen tube. (C) 2004 Elsevier Ireland Ltd. All rights reserved.