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Silk and Pollen Water Potentials in Maize¹

Sexual reproduction depends on the transport of the male gamete to the egg along an aqueous path. In plants, this process causes reproduction to be particularly vulnerable to low water potentials (low _W). Crops experience large yield losses when low _W occur during reproduction, but the _W are unknown for most floral parts in relation to the vegetative plant. Therefore, in maize (Zea mays L.) we measured the _W of the pollen and stigmas (silks), two structures important to the fertilization process, and compared the _W to those in the leaves. Plants were grown in the field and in a controlled environment in soil. When water was supplied, leaf _W varied diurnally between –0.15 and –0.7 MPa. However, silk _W showed little diurnal variation and ranged between –0.3 and –0.6 MPa. Freshly released pollen began the day at much lower _W (–1.2 MPa) and decreased to very low _W (–12.5 MPa) as the day progressed. Similar _W were observed in the controlled environment and in the field. When water was withheld, leaf _W decreased to about –1.7 MPa, silk _W decreased to about –1.2 MPa, but pollen _W was unaffected. Silk _W followed changes in leaf _W(r = 0.77) but pollen _W did not (r = 0.28). These observations indicate that stigmatic tissues (silks) are in moderate hydraulic contact with the vegetative plant but the mature male gametophytes (pollen) are not. As a consequence, depletion of soil water affects the silks more than the pollen. This may explain earlier reports that low leaf _W. had no effect on in vitro pollen germination. Also, the data show that pollen _W is always substantially lower then silk _W, assuring that water moves from the silks to the pollen. Because pollen having _W as low as –12.5 MPa has been reported to be viable, pollen desiccation should not be a factor limiting grain production in maize in the field.

Key Words: Water deficits • Silk water potential • Pollen water potential • Zea mays L.

² Plant physiologist, USDA-ARS, North Central Soil Conserv. Res. Lab., Morris, MN 56267; plant physiologist and professor, Dep. of Soil and Crop Sciences, Texas A&M Univ. College Station, TX 77843.

Received for publication August 28, 1985.

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