The data obtained characterize the changes in the contents of endogenous phytohormones (IAA, cytokinins, GA, and ABA) in germinating pollen grains and growing pollen tubes of a self-compatible clone of petunia ( Petunia hybrida L.) within an 8-h period under in vitro conditions. The hydration and initiation of germination of pollen grains brought the ABA content down to a zero level, while the levels of GA, IAA, and cytokinins increased 1.5-2-fold. Later, in the growing pollen tubes, the GA content increased twofold, while the levels of IAA and cytokinins decreased. The exogenous ABA and GA 3 considerably promoted pollen germination and pollen tube growth; however, only the treatment with GA 3 produced the maximum length of pollen tubes. The exogenous IAA promoted and the exogenous cytokinins hindered the growth of pollen tubes. The membrane potential, as assessed with a potential-sensitive dye diS-C 3 -(5), considerably increased in the pollen grains treated with ABA and benzyladenine, whereas IAA and GA 3 did not practically affect it. The authors conclude that the mature pollen grains contain the complete set of hormones essential for pollen germination and pollen tube growth. ABA, GA, and IAA together with cytokinins control the processes of pollen grain hydration, germination, and pollen tube growth, respectively.
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