Journal of Plant Physiology 168 (2011) 441–448 Contents lists available at ScienceDirect Journal of Plant Physiology journal homepage: www.elsevier.de/jplph Diurnal pollen tube growth rate is slowed by high temperature in field-grown Gossypium hirsutum pistils John L. Snider a,∗ , Derrick M. Oosterhuis b , Eduardo M. Kawakami b a USDA-ARS, Dale Bumpers Small Farm Research Center, 6883 South State Highway 23, Booneville, AR 72927, USA b Department of Crop, Soil, and Environmental Sciences, University of Arkansas, 1366 West Altheimer Drive, Fayetteville, AR 72704, USA article info Article history: Received 12 July 2010 Received in revised form 12 August 2010 Accepted 13 August 2010 Keywords: Fertilization Gossypium hirsutum Heat stress Pollen germination Pollen tube growth abstract For Gossypium hirsutum pollination, germination, and pollen tube growth must occur in a highly con- certed fashion on the day of flowering for fertilization to occur. Because reproductive success could be influenced by the photosynthetic activity of major source leaves, we hypothesized that increased temper- atures under field conditions would limit fertilization by inhibiting diurnal pollen tube growth through the style and decreasing subtending leaf photosynthesis. To address this hypothesis, G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures while at the same developmental stage (node 8 above the cotyledons). Collection and measurement were con- ducted at 06:00, 09:00, 12:00, 15:00, and 18:00 h on August 4 (34.6 ◦ C maximum air temperature) and 14, 2009 (29.9 ◦ C maximum air temperature). Microclimate measurements included photosynthetically active radiation, relative humidity, and air temperature. Pistil measurements included pistil surface tem- perature, pollen germination, pollen tube growth through the style, fertilization efficiency, fertilized ovule number, and total number of ovules per ovary. Subtending leaf measurements included leaf tempera- ture, photosynthesis, and stomatal conductance. Under high temperatures the first measurable pollen tube growth through the style was observed earlier in the day (12:00 h) than under cooler conditions (15:00 h). Also, high temperature resulted in slower pollen tube growth through the style (2.05 mm h -1 ) relative to cooler conditions (3.35 mm h -1 ), but there were no differences in fertilization efficiency, num- ber of fertilized ovules, or ovule number. There was no effect of sampling date on diurnal photosynthetic patterns, where the maximum photosynthetic rate was observed at 12:00 h on both dates. It is con- cluded that, of the measured physiological and reproductive processes, pollen tube growth rate showed the greatest sensitivity to high temperature under field conditions. Published by Elsevier GmbH. 1. Introduction The day of anthesis is a critical event in the reproductive devel- opment of cotton (Gossypium hirsutum). The first flower is produced approximately 8 weeks following plant emergence, and flowers are continually produced by the same plant throughout the growing season due to the indeterminate growth habit of the cotton plant (Oosterhuis, 1990). On the day of anthesis, a white flower opens at dawn (Stewart, 1986) with pollination reported to occur between 07:00 and 11:00 h (Pundir, 1972) and germination within 30 min following pollination (Stewart, 1986). The pollen tube extends through the transmitting tissue of the style and fertilization of the ovule occurs between 12 and 24 h later (Stewart, 1986). Abbreviations: PAR, photosynthetically active radiation; PFD, photon flux den- sity; RH, relative humidity; T air , air temperature; T leaf , leaf temperature; T pistil , pistil temperature. ∗ Corresponding author. Tel.: +1 479 675 3834x342; fax: +1 479 675 2940. E-mail address: John.Snider@ars.usda.gov (J.L. Snider). Because a number of reproductive processes must occur in a highly concerted fashion for fertilization to occur, sexual reproduc- tion is only as tolerant to heat stress as the most thermosensitive process (Hedhly et al., 2009; Zinn et al., 2010). As a consequence, the yield of plant species with reproductive structures of agricultural importance is exceptionally sensitive to high temperature stress during flowering (Sato et al., 2001; Oosterhuis, 2002; Pettigrew, 2008). Heat stress can limit fertilization by inhibiting male (Jain et al., 2007) and female (Saini et al., 1983) gametophyte development, pollen germination (Burke et al., 2004; Kakani et al., 2005; Jain et al., 2007), and pollen tube growth (Burke et al., 2004; Hedhly et al., 2004; Kakani et al., 2005). Recent reviews by Hedhly et al. (2009) and Zinn et al. (2010), have suggested that pollen development and function may be the most thermosensitive reproductive pro- cesses to high temperature. For example, chronic high temperature exposure during the meiotic phase of microgametophyte develop- ment results in poor pollen germination and seed set in Sorghum bicolor (e.g. Jain et al., 2007). Both in vivo (Hedhly et al., 2004) and in vitro (Burke et al., 2004; Kakani et al., 2005) studies utilizing short- 0176-1617/$ – see front matter. Published by Elsevier GmbH. doi:10.1016/j.jplph.2010.08.003