Reproductive and vegetative tissues of the seeded Pineapple cultivars of sweet orange (Citrus sinensis L.) contained the following C-13 hydroxylated gibberellins (CAs): CA,,, GA, , , CA,,, CA,,, CA,, CA,,, and CA,, as well as CA,,, 3-epi-CA1, and several uncharacterized CAs. l h e inclusion of 3-epi-CA, as an endogenous substance was based on measurements of the isomerization rates of previously added [2H,]CA,. Pollination enhanced amounts of CA,,, CA,,, CA,,, and GA, in developing ovaries. Levels of CA, increased from 5.0 to 9.5 ng/g dry weight during anthesis and were reduced thereafter. l h e amount of GA in mature pollen was very low. Emasculation reduced C A levels and caused a rapid 100% ovary abscission. This effect was partially counteracted by either pollination or application of GA,. In pollinated ovaries, repeated paclobutrazol applications decreased the amount of C A and increased ovary abscission, although the pattern of continuous decline was different from the sudden abscission induced by emasculation. l h e above results indicate that, in citrus, pollination increases CA levels and reduces ovary abscission and that the presence of exogenous CA, in unpollinated ovaries also suppresses abscission. Evidence is also presented that pollination and CAs do not, as is generally assumed, suppress ovary abscission through the reactivation of cell division.

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Clementine (Citrus reticulata [Hort.] Ex. Tanaka cv. Oroval) is a self‐incompatible mandarin with a slow rate of fruit growth and high percentage of fruit abscission. Seedless Satsuma (Citrus unshiu [Mak] Marc. cv. Clausellina) shows natural parthenocarpy and higher fruit set. Application of 25 μg fruit−1 of paclobutrazol (PP333), an inhibitor of gibberellin biosynthesis, reduced the rate of growth and accelerated fruit abscission in both varieties. In contrast, gibberellin A3 (GA3) stimulated fruit growth only in the self‐incompatible mandarin. Clementine fruits, in the absence of pollination, showed an approximately 2‐fold transient increase in the free abscisic acid (ABA) content shortly after petal fall. In Satsuma, a very small accumulation of ABA was detected. Paclobutrazol treatment induced a 3‐fold increase in ABA in Satsuma fruits but did not substantially affect the pattern of ABA accumulation in Clementine. In this variety, GA3 suppressed the ABA increase observed in untreated fruits. These effects were observed 24 h after treatment. However, in Satsuma fruits, the effect of GA3 on the ABA content was negligible. In addition, a comparative analysis of growing and non‐growing fruits of Clementine showed that ABA, on a per unit weight basis, was always higher in the non‐growing fruits. Treatment with 85 μM fluridone, an inhibitor of carotenoid biosynthesis and thus indirectly of ABA, delayed fruit abscission in Clementine, but also decreased fruit growth. Collectively, these observations indicate a relationship between high ABA content and a reduced rate of fruit growth and an acceleration of fruit abscission.

The involvement of gibberellins (GAs) and ethylene in the process of root radial expansion was studied in young seedlings of Carrizo citrange [Citrus sinensis (L.) Osb.´Poncirus trifoliata (L.) Raf.]. The GA inhibitors cycocel, paclobutrazol, and tetcyclacis enhanced radial expansion of the root tip (up to 2.3-fold) as a result of increases in stele diameter and inner cortex width. The GA de®ciency increased cell number and width, and changed the polarity of growth, generating wider and shorter cortical cells in the elongation zone. In the presence or absence of GA inhibitors, GA 3 decreased root tip width and reduced all parameters related to radial expansion. The ethylene inhibitors (aminooxyacetic acid; cobalt ions, CoCl 2 ; silver thiosulfate) suppressed swelling induced by GA de®ciency, generating thinner cells just as GA 3 did. In contrast to GA 3 , ethylene inhibitors produced longer cells strongly resembling those of the untreated seedlings. Ethylene released by ethephon did not modify root tip width in control plants, while root diameter behind the root tip was increased. In the presence of low and ineective concentrations of cycocel, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid increased radial expansion of root tips (1.3-fold) and changed the polarity of growth, producing wider and shorter inner cortical cells as GA inhibitors did. These observations imply, ®rst, that ethylene is the hormonal eector of the process of root radial expansion and, second, that the endogenous GAs modulate the promotive response of ethylene.Abbreviations: ACC = 1-aminocyclopropane-1-carboxylic acid; AOA = aminooxyacetic acid; CCC = cycocel; GA = gibberellin; GA 3 = gibberellic acid; IC = inner cortex; PCB = paclobutrazol; STS = silver thiosulphate; TTC = tetcyclasis Correspondence to: M. Talo n; Fax: 34 (6) 1390240;