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In Vitro Analysis of Cotton Pollen Germination

USDA-ARS, SPA, Plant Stress and Water Conserv. Lab., Lubbock, TX 79415

View larger version (128K): [in a new window]   Fig. 1. Photomicrograph of Gregg 65 cotton pollen exposed to 28°C on the pollen germination medium for 180 min. The graphs show the temperature dependence of pollen germination and pollen tube elongation of PM2156, PM2326, and DP90 cotton compared with samples incubated at 28°C. The three replicate samples for each of the three cultivars were combined and the percentage germination and relative pollen tube lengths evaluated. The data show reduced pollen germination at 40°C and above (LSD = 22.89) while pollen tube length was reduced with temperatures of 34°C or above (LSD = 15.201). Error bars represent standard errors.

View larger version (168K): [in a new window]   Fig. 2. Photomicrographs of PM2200, PM2156, PM2326, DP90, SG521, and Pima S-7 pollen on the pollen germination medium following a 90-min incubation at 28°C. Pollen germination and pollen tube elongation were observed in all cultivars tested.

View larger version (77K): [in a new window]   Fig. 3. Photomicrographs of (A) corn cultivar DK626 pollen, (B) soybean cultivar Mitchell 450 pollen, and (C) tobacco cultivar SR1 pollen on the solid medium developed for cotton pollen germination. Pollen germination and pollen tube development were apparent in all three species.

View larger version (88K): [in a new window]   Fig. 4. Representative photomicrographs of Gregg 65 cotton pollen incubated at 28°C for 180 min on the pollen germination medium with surrounding relative humidity (RH) levels of 35%, 50 to 80%, and 100%. Pollen tube elongation was reduced at 35%, and pollen tubes ruptured in a 100% RH. Maximum pollen tube elongation occurred between 50 and 80% RH.

View larger version (102K): [in a new window]   Fig. 5. Representative photomicrographs of Gregg 65 cotton pollen incubated on pollen germination media having pH values ranging from 8.0 to 6.0. Similar pollen tube elongation and pollen germination were observed across this range of pH values.

View larger version (107K): [in a new window]   Fig. 6. Photomicrographs of cotton pollen incubated for 120 min on a germination media containing (A) sucrose, (B) glucose, (C) maltose, and (D) fructose. Relative pollen tube lengths are provided in the graph. Maximum germination and pollen tube elongation occurred in the sucrose-containing medium.

View larger version (80K): [in a new window]   Fig. 7. Representative photomicrographs showing the time course of cotton pollen germination and pollen tube elongation at 28°C. Relative pollen tube lengths determined at 30-min intervals are provided in the graph.

View larger version (41K): [in a new window]   Fig. 8. (A) Photomicrograph of cotton pollen incubated at 22°C for 5 h, and (B) diagram of the path of pollen tube development of a single pollen grain shown in (A).

View larger version (23K): [in a new window]   Fig. 9. Graph of anther temperatures of flowers shaded by the canopy (open bars) and flowers exposed to the full sun (solid bar) from 1000 to 1600 h. Elevated temperatures were seen in the flowers exposed to full sunlight at all measurement times compared with flowers shaded by the canopy.

View larger version (70K): [in a new window]   Fig. 10. Diagram of a cotton plant illustrating the relative position of flowers measured in the (A) shade and (B) sun at 1400 h. The photomicrographs show pollen incubated on the germination media at 28°C for 120 min of pollen taken from (A) shaded flowers and (B) flowers exposed to full sun. Greater pollen germination and pollen tube length are seen in flowers that were shaded.