Gibberellin metabolism in cell-free extracts from spinach leaves in relation to photoperiod

• Published in: Plant physiology (Bethesda) 1986-09, Vol.82 (1), p.190-195
• Main Authors: Gilmour, Sarah J., Jan A. D. Zeevaart, Ludger Schwenen, Graebe, Jan E.
• Format: Article
• Language: English
• Subjects: acido giberelico; actividad enzimatica; activite enzymatique; Agronomy. Soil science and plant productions; analisis de tejidos; analyse de tissus; Biological and medical sciences; Cell free system; Cellular metabolism; Economic plant physiology; Enzyme activity; Enzyme preparations; Enzymes; enzymic activity; extractos; extracts; extrait; fonction physiologique; fotoperiodismo; funcion fisiologica; Fundamental and applied biological sciences. Psychology; gibberelline; Gibberellins; Growth and development; Growth regulators; Leaves; Metabolism; metabolisme; metabolismo; Photoperiod; photoperiodicite; photoperiodicity; physiological functions; Plant physiology and development; Plants; Spinach; spinacia oleracea; tissue analysis
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.82.1.190

Cell-free extracts capable of converting [14C]-labeled gibberellins (GAs) were prepared from spinach (Spinacia oleracea L.) leaves. [14C]-labeled GAs, prepared enzymically from [14C]mevalonic acid, were incubated with these extracts, and products were identified by gas chromatography-mass spectrometry. The following pathway was found to operate in extracts from spinach leaves grown under long day (LD) conditions: $\text{GA}_{12}$ → $\text{GA}_{53}$ → $\text{GA}_{44}$ → $\text{GA}_{19}$ → $\text{GA}_{20}$. The pH optima for the enzymic conversions of $[{}^{14}\text{C}]\text{GA}_{53}$, $[{}^{14}\text{C}]\text{GA}_{44}$ and $[{}^{14}\text{C}]\text{GA}_{19}$ were approximately 7.0, 8.0, and 6.5, respectively. These three enzyme activities required Fe2+, α-ketoglutarate and O2 for activity, and ascorbate stimulated the conversion of $[{}^{14}\text{C}]\text{GA}_{53}$ and $[{}^{14}\text{C}]\text{GA}_{19}$. Extracts from plants given LD or short days (SD) were examined, and enzymic activities were measured as a function of exposure to LD, as well as to darkness following 8 LD. The results indicate that the activities of the enzymes oxidizing $\text{GA}_{53}$ and $\text{GA}_{19}$ are increased in LD and decreased in SD or darkness, but that the enzyme activity oxidizing $\text{GA}_{44}$ remains high irrespective of light or dark treatment. This photoperiodic control of enzyme activity is not due to the presence of an inhibitor in plants grown in SD. These observations offer an explanation for the higher $\text{GA}_{20}$ content of spinach plants in LD than in SD.