280 J. AMER. SOC. HORT. SCI. 129(3):280–286. 2004. J. AMER. SOC. HORT. SCI. 129(3):280–286. 2004. Endogenous Free Polyamines of Mangos in Relation to Development and Ripening Aman Ullah Malik and Zora Singh 1 Horticulture/Viticulture, Muresk Institute, Division of Resources and Environment, Curtin University of Technology, GPO Box U 1987, Perth 6845 Western Australia ADDITIONAL INDEX WORDS. putrescine, spermine, spermidine, cell division, ovule, skin, pulp, ethylene, Mangifera indica ABSTRACT. Changes in endogenous free polyamines (putrescine, spermidine, spermine) were monitored from fruit set (fruit diameter 4.6 ± 0.5 mm, wt 0.09 ± 0.05 g) until 1 week before the expected harvest time in ‘Kensington Prideʼ and ‘Glenʼ to examine their role during mango (Mangifera indica L.) fruit development. Polyamines (PAs) in the pericarp tissues (exocarp and mesocarp) were estimated throughout the fruit development period, while estimations from growing ovules were started from 41 days after fruit set (DAFS). During fruit ripening, ethylene production and endogenous free PAs in skin and pulp of ‘Kensington Prideʼ mango were also monitored. PA contents of pericarp declined between fruit set and maturity from 788 to 101 nmol·g –1 fresh weight (FW) in ‘Kensington Prideʼ and from 736.6 to 89.6 nmol·g –1 FW in ‘Glenʼ during fruit development. Spermidine (SPD) and spermine (SPM) were higher than putrescine (PUT) during the initial phase of fruit growth. The highest levels of free PAs, especially SPD and SPM, at the initial stages of fruit growth suggest a potential role during the cell division phase and not in subsequent fruit development. Ovule seems to be a rich source of PAs as evident from 2.3- and 2.7-fold higher total PAs than pericarp tissues in ‘Kensington Prideʼ and ‘Glenʼ, respectively. During fruit ripening of ‘Kensington Prideʼ, total PAs increased in skin and pulp tissues along with the climacteric rise of ethylene, and reached maximum levels (skin 796, pulp 314 nmol·g –1 FW) on day 4 of ripening. Skin exhibited 55.8% higher mean free PAs than the pulp. PUT dominated both in skin and pulp tissues. The simultaneous increase of ethylene and free PAs during fruit ripening suggests that their biosynthesis may not be competitive, and free PAs may have evolved as a response to increased biosynthesis of ethylene. Mango fruit growth and development have been associated with changes in endogenous plant growth substances (Ram, 1992). Endogenous levels of auxins, gibberellins, cytokinins, abscissic acid (ABA) and ethylene have been determined during mango fruit growth and development (Murti and Upreti, 1995; Ram, 1992). However, biosynthesis and distribution of PAs in relation to mango fruit growth and development is yet unknown. PAs are implicated in fruit growth and development because of their ubiquitous pres- ence in all cells (Smith, 1985). Putrescine (PUT), spermidine (SPD), and spermine (SPM), are the most commonly found polyamines (PAs) in plants. Changes in PAs during fruit development and ripening imply a significance in such processes, however, the precise role of PAs is not clear (Shiozaki et al., 2000). Exogenous application of PAs have been reported to increase the endogenous levels of PAs and fruit size (Biasi et al., 1991), indicating that the lower levels of these com- pounds could be growth limiting. Higher endogenous PAs level is also correlated with tolerance against a number of biotic and abiotic stresses (Bouchereau et al., 1999). Polyamines are synthesized from ornithine, arginine, and S-adenosyl methionine (SAM) and three of the enzymes involved are amino acid decarboxylases (Malmberg et al., 1998). PAs share a common precursor with ethylene (SAM), but show opposite effects in relation to the senescence processes Received for publication 11 May 2003. Accepted for publication 4 Dec. 2003. We are thankful to Westralian Fruits, Gingin, Western Australia for provision of mango trees and other facilities used to conduct this study. We also thank Sandro Bambardieri and Peter Sheppard for their assistance in the analysis of polyamines. The authors are grateful to A.S. Basra, J.K. Brecht (Univ. Florida), and M.H. Behboudian (Massey Univ., New Zealand) for critically review of this manuscript. A. U. Malik also acknowledges the financial support of Curtin Uni- versity of Technology, Perth, Western Australia, for an International Postgraduate Research Scholarship, the Australian International Development Program for an ADS scholarship, and the University of Agriculture, Faisalabad, Pakistan, for granting study leave during this period. 1 To whom reprint requests should be addressed; e-mail Z.Singh@curtin.edu.au. (Kakkar and Rai, 1993). The mechanism by which they interact with each other is not yet clear. Mutational and transgenic studies suggest interactions between endogenous PAs and either ethylene or cytokinins (Malmberg et al., 1998) and demonstrate the role of PAs in growth, development and ripening (Kumar et al., 1996). Higher levels of PAs during the initial fruit growth period, pro- gressively declining toward maturity, have been reported in various fruits including apple (Malus domestica Borkh.) (Biasi et al., 1988), grapes (Vitis vinifera L.) (Geny et al., 1997), tomato (Lycopersicon esculentum Mill.) (Morilla et al., 1996), and peach (Prunus perscia L.) (Kushad, 1998). However, in muskmelon (Cucumis melo L.), SPM and PUT increased with fruit development until 35 d after anthesis (Lester, 2000). During fruit ripening, increased levels of PAs have been reported in mandarins (Citrus reticulata Blanco ‘Murcottʼ) (Nathan et al., 1984), cherimoya (Annona cherimola Mill.) (Escribano and Merodio, 1994), and rambutans (Nephelium lappesium L.) (Kondo et al., 2001). However, in plum (Prunus salicina Lindl.), ‘Golden Japanʼ, which exhibited a nonclimacteric ripening process showed increased PAs toward maturity compared to ‘Santa Rosaʼ, which had a climacteric pattern of ripening (Zu- zunaga et al., 2001). Thus, it may be surmised that variation in the trends of PAs biosynthesis and their endogenous levels not only exist between different species but also within a species and with differences in tissue types and stages of development. The role of the embryo in fruit development should also be taken into account, since seeds are considered as a source of phy- tohormones (Nitsch, 1970). In peaches, seed tissues exhibited a burst of PAs during the pit hardening stage, but the levels of PAs in mesocarp tissues did not increase (Kushad, 1998). Contrarily in grapes, the increase in PAs in seeds corresponded to the time of PAs increase in mesocarp (Shiozaki et al., 2000). In mango, the work related to endogenous PAs has been limited to fruitlet abscission (Malik and Singh, 2003a; Murti and Upreti, 1999) and chilling injury (Nair, 2002; Whangchai et al., 2000). The poten- tial role of the embryo in relation to changes in PAs during fruit