Silk and Pollen Water Potentials in Maize1
- Mark E. Westgate and
- John S. Boyer2
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 ψW). Crops experience large yield losses when low ψW occur during reproduction, but the ψW are unknown for most floral parts in relation to the vegetative plant. Therefore, in maize (Zea mays L.) we measured the ψW of the pollen and stigmas (silks), two structures important to the fertilization process, and compared the ψW to those in the leaves. Plants were grown in the field and in a controlled environment in soil. When water was supplied, leaf ψW varied diurnally between −0.15 and −0.7 MPa. However, silk ψW showed little diurnal variation and ranged between −0.3 and −0.6 MPa. Freshly released pollen began the day at much lower ψW (−1.2 MPa) and decreased to very low ψW (−12.5 MPa) as the day progressed. Similar ψW were observed in the controlled environment and in the field. When water was withheld, leaf ψW decreased to about −1.7 MPa, silk ψW decreased to about −1.2 MPa, but pollen ψW was unaffected. Silk ψW followed changes in leaf ψW(r = 0.77) but pollen ψW 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 ψW. had no effect on in vitro pollen germination. Also, the data show that pollen ψW is always substantially lower then silk ψW, assuring that water moves from the silks to the pollen. Because pollen having ψW 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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