AXILLARY BUD DEVELOPMENT OF PASSIONFRUIT AS AFFECTED BY ETHYLENE PRECURSOR AND INHIBITORS L. B. REIS 1 , V. B. PAIVA NETO 1 , E. A. TOLEDO PICOLI 1 , M. G. C. COSTA 1 , M. M. RE ˆ GO 2 , C. R. CARVALHO 3 , F. L. FINGER 2 , AND W. C. OTONI 1 * 1 Departamento de Biologia Vegetal, 2 Departamento de Fitotecnia, and 3 Departamento Biologia Geral, Universidade Federal de Vic ¸osa, Av. P. H. Rolfs, s/n, Campus Universita ´ rio, 36571-000, Vic ¸osa, MG, Brazil (Received 30 October 2002; accepted 30 April 2003; editor F. A. Krens) Summary The effects of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and two inhibitors, silver thiosulfate (STS) and aminoethoxyvinylglycine (AVG), were tested in yellow passionfruit (Passiflora edulis f. flavicarpa Degener) axillary buds cultured in vitro. The organogenic responses were assessed by the number of buds per explant, mean leaf area per explant, and shoot length. ACC-supplemented medium significantly inhibited all evaluated responses at both concentrations tested. When ethylene action and biosynthesis were inhibited, a significant increase in the number of developed buds and average leaf area was observed. Accumulated ethylene and its accumulation rate were significantly greater at 10 mM ACC, with a maximum production rate detected: at the 14th day and a decline at the 21st day. The results suggest beneficial effects of ethylene inhibitors on in vitro development of axillary buds and their reliability for use as an alternative approach to evaluate sensitivity of Passiflora species to ethylene. Even though shoot elongation did not differ from that of the control, the inhibition of the ethylene action and its biosynthesis by AVG and STS, respectively, significantly enhanced the number of buds per explant and leaf area. Key words: plant tissue culture; ethylene; Passiflora edulis f. flavicarpa Degener; shoot culture. Introduction Passionfruit is a large genus of perennial climbing edible fruits. Passiflora edulis f. flavicarpa, namely yellow passionfruit, is thought to have originated from tropical areas of Brazil and is one of the most economically important species of the Passifloraceae family. The fruit has become a popular source of juice and a good source of vitamins A and C (Arjona and Matta, 1991; Taylor, 1993). However, the availability of fresh fruit is limited by irregular supply and short post-harvest shelf-life (Pocasangre-Enamorado et al., 1995). Propagation of passionfruit is performed predominantly by means of sexual reproduction (Meletti and Maia, 1999). This is a consequence of floral characteristics and self-incompatibility, which lead to a practice that produces plants with high genetic variability and non-uniformity with regard to agronomic traits. Plant tissue culture may be an important tool to propagate superior genotypes. Passionfruit micropropagation is far from being routine due to low multiplication rates, even though several studies have been reported (Kantharajah and Dodd, 1990; Drew, 1991; Kawata et al., 1995; Faria and Segura, 1997; Monteiro et al., 2000). As a climacteric fruit, Passiflora spp. shows high rates of ethylene production (Pocasangre-Enamorado et al., 1995; Shiomi et al., 1996), which may also limit the in vitro morphogenic potential of the explanted cultures. Ethylene plays a role in several in vitro developmental processes (Matthijs et al., 1995; Biondi et al., 1998; Kumar et al., 1998). However, its contribution to in vitro plant development is still unclear, even when different species, explants, regeneration pathways, development status, interaction with other growth regulators, and culture conditions are concerned (Huxter et al., 1981; George, 1993; Nissen, 1993; Pua et al., 1996; Magdalita et al., 1997; Biondi et al., 1998; Pua, 1999). To date, Faria and Segura (1997) and Barbosa et al. (2001) are the only reports on the effects of ethylene on in vitro morphogenesis of passionfruit. The effects of ethylene on in vitro development of passionfruit axillary bud have not been investigated, although Barbosa et al. (2001) had demonstrated the sensitivity of P. edulis f. flavicarpa shoot apices to this growth regulator. Intense chlorosis, as detected by the decrease in pigment content, was observed with 3, 10, and 30 mM 1-aminocyclopropane-1-carboxylic acid (ACC), which led to plant senescence. Similarly, in the ACC treatments, a reduced number and length of differentiated roots was observed (Barbosa et al., 2001). Likewise, Faria and Segura (1997) stated that passionfruit cotyledonary explant regeneration was improved when ethylene inhibitors were added to the culture medium. The inclusion of silver thiosulfate (STS) in the culture medium significantly increased the differentiation and development of adventitious shoots from hypocotyl and leaf explants of P. edulis f. flavicarpa. However, no ethylene quantification during the culture period was made. As a rule, ethylene accumulation occurs in plant tissue culture although varying with species, total content and type of growth *Author to whom correspondence should be addressed: Email wotoni@ ufv.br In Vitro Cell. Dev. Biol.—Plant 39:618–622, November – December 2003 DOI: 10.1079/IVP2003455 q 2003 Society for In Vitro Biology 1054-5476/03 $18.00+0.00 618