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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 I"CiGA,2 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, '4CiGAs3, 4qC]GA44, ['4CJGA,,, and/or I'4C1 GA17, were all elevated in SD as compared to LD. Putative 114CIGA, was slightly higher in LD than in SD. Putative I'4C]GAs3 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 I'4C] GA44 and 114CIGA9/,,1. Metabolism of GA2o was slow in both photoperiods. Although GA2o and GA,9 are the major endogenous GAs as determined by gas chromatography-mass spectrometry, putative j'4CJGA20 and I'4CIGA,, were never major products of I'4C]GA,2 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.In the G2 genetic line of peas (Pisum sativum L.) senescence of the apical bud, which is a prelude to the senescence of the whole plant, takes place only in long photoperiods (17). In short photoperiods growth is indeterminate. The prevention of senescence by SD is associated with the presence of an elevated level

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is not yet understood.It is widely accepted that the transport of Krebs cycle substrate anions by plant mitochondria is by the DC2 and TC transporters disclosed in studies with animal mitochondria (reviewed in Refs. 11 and 30; for animal mitochondria, see Ref. 18). The principal evidence is found in the exchange studies of De Santis et a!. (7), and in passive swelling studies with isosmotic solutions of NH4' salts (25,29). The general conclusion is that the primary transport lies with the exchange of Pi for OH-(or symport of Pi with H+), with DC (e.g. malate, succinate) exchanging for Pi, and TC (e.g. citrate, isocitrate) exchanging for DC (Fig. IA) driven by endogenous respiration or ATP (21).In the work reported here we have used both swelling and ['4C] citrate uptake to study citrate transport in corn mitochondria. There is definitely a mechanism that is not dependent on phosphate or malate transport, and which has characteristics of a H +/ citrate symport (Fig. 1, B and C; see "Discussion").MATERIALS AND METHODS Mitochondria. Corn (Zea mays L. B73 x Mol9) shoot mitochondria were isolated as described ( 17)

Experiments were designed to test the hypothesis that the labeled products recovered from plant tissue incubated with '4"CGA1r7-aldehyde (['4CGA12ald) would serve as appropriate I'Cimarkers for the recovery of naturally-occurring gibberellins (GAs). The I'CIGA12Ald (about 200 millicuries per millimole) was synthesized from pumpkin endosperm using 14,5-ClCmevalonic acid. It was added to the adaxial surface of isolated pea cotyledons at 22 days after flowering. Products recovered after 0.5 and 4.0 hour incubations yielded four major peaks which were separated by high perfornumce liquid chromatography (HPLC). These products were purified by multiple-column HPLC using on-line radioactivity detection. They were then added as I'4C1markers to two unlabeled pea extracts. In general, preparative HPLC followed by further HPLC purification resulted in a single UV-absorbing peak co-eluting with each 114Cimarker. These '4"C and UV-absorbing peaks were shown to contain GAI3, GA4, GA2, GA,, and GA17 by GC-MS. The fmding of GAS3 is novel; all others have previously been found in pea. Endogenous GAs of pea were thus readily detected using ['4CjGA,2ald metabolites as I'4Cimarkers to recover naturally occurring GAs suggesting that the method may be applicable in detecting naturally occurring GAs in other species.