Methionine metabolism and ethylene biosynthesis in senescent flower tissue of morning-glory
In immature rib segments prepared from morning-glory (Ipomoea tricolor) flower buds, the major soluble metabolite formed from tracer amounts of L-methionine-U-/sup 14/C was S-methylmethionine (SMM). In segments of senescing ribs, /sup 14/C was progressively lost from SMM and appeared in free methionine. Immature segments contained about 4 nmoles of free methionine and about 16 nmoles of SMM per 30 segments. As the segments senesced, the methionine content increased about 10-fold while the SMM content remained unchanged; during this time about 0.8 nmole of ethylene was produced per 30 segments. Tracer experiments with L-methionine-U-/sup 14/C, L-methionine-methyl-/sup 3/H, and L-homocysteine thiolactone-/sup 35/S indicated that SMM was capable of acting as a methyl donor, and that in senescent segments the methyl group was utilized for methionine production with homocysteine serving as methyl acceptor. Of the 2 molecules of methionine produced in this reaction, 1 was re-methylated to SMM, and the other contributed to the observed rise in the content of free methionine. Internal pools of methionine and SMM were prelabeled (but not significantly expanded) by overnight incubation on 10 ..mu..ML-methionine-U-/sup 14/C. The specific radioactivity of the ethylene subsequently evolved during the senescence of the segments closely paralleled the specific radioactivity of carbon atoms 3 plus 4 of free methionine extracted from the tissue, demonstrating that methionine was the major precursor of ethylene in this system. The specific radioactivity of carbon atoms 3 plus 4 of extracted SMM was about twice that of the free methionine. Based on these results, a scheme for methionine biosynthesis in senescent rib tissue is presented. The operation of this pathway in the control of ethylene production is discussed.
- Research Organization:
- Michigan State Univ., East Lansing
- OSTI ID:
- 7342750
- Journal Information:
- Plant Physiol.; (United States), Journal Name: Plant Physiol.; (United States) Vol. 57:4; ISSN PLPHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ALKENES
AMINO ACIDS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMISTRY
BIOSYNTHESIS
BUDS
CARBON 14
CARBON ISOTOPES
CARBOXYLIC ACIDS
CHEMISTRY
ENZYMES
ETHYLENE
EVEN-EVEN NUCLEI
FLOWERS
HYDROCARBONS
ISOTOPES
LABELLED COMPOUNDS
LIFE CYCLE
LIGHT NUCLEI
LIPOTROPIC FACTORS
METABOLISM
METHIONINE
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PRECURSOR
RADIOISOTOPES
SYNTHESIS
YEARS LIVING RADIOISOTOPES