Photoperiod Modification of [¹⁴C]Gibberellin A₁₂ Aldehyde Metabolism in Shoots of Pea, Line G2

Abstract

In G2 peas (Pisum sativum L.) apical senescence occurs only in long days (LD), and indeterminate growth is associated with elevated gibberellin (GA) levels in the shoot in short days (SD). Metabolism of GA₁₂ aldehyde was investigated by feeding shoots grown in SD or LD with [¹⁴C]GA₁₂ aldehyde through the cut end of the stem for 0.5 to 6 hours in the light and analyzing the tissue extract by high performance liquid chromatography. More radioactive products were detected than can be accounted for by the two GA metabolic pathways previously known to be present in peas. Three of the major products appear to be GA conjugates, but an additional pathway(s) of GA metabolism may be present. The levels of putative C₂₀ GAs, [¹⁴C]GA₅₃, [¹⁴C]GA₄₄, [¹⁴C]GA₁₉, and/or [¹⁴C] GA₁₇, were all elevated in SD as compared to LD. Putative [¹⁴C]GA, was slightly higher in LD than in SD. Putative [¹⁴C]GA₅₃ was a major metabolite after 30 minutes of treatment in SD but had declined after longer treatment times to be replaced by elevated levels of putative [¹⁴C] GA₄₄ and [¹⁴C]GA_19/17. Metabolism of GA₂₀ was slow in both photoperiods. Although GA₂₀ and GA₁₉ are the major endogenous GAs as determined by gas chromatography-mass spectrometry, putative [¹⁴C]GA₂₀ and [¹⁴C]GA₁₉ were never major products of [¹⁴C]GA₁₂ aldehyde metabolism. Thus, photoperiod acts in G2 peas to change the rate of GA₅₃ production from GA₁₂ aldehyde, with the levels of the subsequent GAs on the 13-OH pathway being determined by the amount of GA₅₃ being produced.