THE MALE GAMETOPHYTE OF ZEA MAYS L.: III. THE INFLUENCE OF TEMPERATURE AND CALCIUM ON POLLEN GERMINATION AND TUBE GROWTH

Abstract

Corn pollen germination on an aqueous medium containing sucrose, calcium, boron, and 1% methyl cellulose produced tubes which attained growth rates of 12 μ/min at 30 °C. After 30 to 60 min they fell to about half this value. Rates of elongation in the early stages of growth increased with a Q₁₀of 2 between 12 and 30 °C. The time required for the initiation of germination is a hyperbolic function of temperature. Maximum germination occurred at 20–23 °C; maximum rate of elongation during the first hour at 30–33 °C.Only a trace of germination occurred below 50 p.p.m. CaCl₂∙2H₂O and maxi mum at 250–300 p.p.m. Calcium levels had no effect on the time of initiation of germination, on the rate of elongation at 30 °C nor on the mean tube lengths after 30 min and 60 min of germination. A "population effect" was evident on the aqueous medium and was more pronounced at low levels of calcium.Two types of tests produced no evidence of a chemotropic response of pollen tubes to a calcium gradient. Pieces of style and endosperm also gave negative results. The pollen tube growth rates and lengths attained indicate that we are not yet able to control the factors for sustained growth. Some possible factors are discussed.