N4-Hexanoylspermidine, a New Polyamine-Related Compound That Accumulates during Ovary and Petal Senescence in Pea

A previously unknown polyamine conjugate that accumulates in senescing ovaries of pea (Pisum sativum L.) was shown by mass spectrometry, nuclear magnetic resonance, and chemical synthesis to be N4-hexanoylspermidine (hexanoyl-spd) This structure was indicated by analysis of the dansylated polyamine using fast atom bombardment mass spectrometry, following purification by high-performance liquid chromatography. Furthermore, acid hydrolysis of the compound yielded spermidine and hexanoic acid. 1H-nuclear magnetic resonance suggested that spermidine was substituted at N4 in the conjugate. Hexanoyl-spd was synthesized, and its didansyl derivative was shown to have an identical mass spectrum and high-performance liquid chromatography retention time as the derivatized natural compound. Further confirmation of its structure was obtained by comparison of the synthetic and natural polyamines as trifluoroacetyl derivatives using gas chromatography-mass spectrometry. This new polyamine conjugate is present in pea ovaries at low levels at anthesis and its concentration remains low in developing seeded fruit or in parthenocarpic fruit that have been induced by application of growth regulators to emasculated flowers or by topping the plant. Conjugate levels are also low in parthenocarpic fruit induced naturally in the slender (la crys) mutant. However, levels of hexanoyl-spd increase progressively in senescing petals and ovaries, beginning at anthesis or 2 d later, respectively.