Polyamines and Regulation of Ripening and Senescence - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 326

life, it increased during ripening in Liberty, a variety with prolonged shelf life (Saftner and
Baldi, 1990). Liberty also contained three to six times more PAs than Rutgers and Pik Red
and produced only 16 and 38% of ethylene produced by Pik Red and Rutgers, respectively.
Application of 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception, delayed
ripening in tomato fruits, and reduced free Put levels that increased when these fruits started
to ripen, suggesting a role of PAs during fruit ripening (Tassoni et al., 2006b). Similar trends
were observed in other slow- and fast-ripening tomato cultivars (Martinez-Madrid et al.,
1996). Japanese pear cultivars with longer shelf life exhibit higher levels of PAs and show
a negative correlation between PA levels and the rate of ethylene production (Mora et al.,
2005). In nectarines, exogenous application of Put and Spd reduced ethylene production,
delayed loss of firmness, retained titratable acidity, and prevented the increase in dry matter
and soluble solids concentration (Torrigiani et al., 2004). Put treatment also downregulated
expression of ACC oxidase and SAM decarboxylase at the transcriptional level suggesting
that applied PAs affect fruit ripening by altering ethylene biosynthesis. On the other hand,
transgenic tomato expressing yeast SAM decarboxylase showed increased biosynthesis of
both PAs and ethylene, indicating that endogenous level of SAM is not rate limiting for
either pathway during fruit ripening (Mehta et al., 2002). Based on the effects of 1-MCP on
free Put levels and expression of its biosynthetic enzymes, Tassoni et al. (2006b) reached a
similar conclusion.
Carotenoid metabolism in tomato that is tightly linked to ripening is associated with
differentiation of chloroplasts into chromoplasts and is extensively regulated at the tran-
scriptional level (Bramley, 2002; Cookson et al., 2003). Tomato fruit overexpressing the
yeast SAMdc had increased conversion of Put into higher PAs with severalfold increase in
Spd and Spm in ripening fruits. These fruits exhibited a two- to threefold increase in ly-
copene (a nutritionally important antioxidant), prolonged vine life, and enhanced fruit juice
quality (Mehta et al., 2002). Although these studies suggest a role for PAs in influencing
carotenoid metabolism, further studies are needed to probe a direct link between PAs and
carotenoid metabolism.

15.7 Polyamines and postharvest shelf life

Ripe fruit of “ alcobaca ” landrace tomato variety exhibited prolonged keeping qualities
and contained three times more Put than a control variety, “Rutgers” (Dibble et al.,
1988). As both genotypes showed similar catabolism of Put and Spd, increased ADC
activity has been suggested to be the cause of elevated levels of Put in alcobaca fruits
(Rastogi and Davies, 1991). Transgenic tomato fruits that accumulate higher levels of
Spd and Spm due to the expression of SAM decarboxylase showed prolonged vine life
(Mehta et al., 2002). Vacuum infiltration of tomato fruit with Put, Spd, Spm, diamino-
propane, -aminobutyric acid, and methionine increased their storage life (Law et al., 1991).

Pomegranate fruits treated with Put or Spd, either by pressure infiltration or immersion, and
subsequently stored at 2 ◦ C for 60 days had higher levels of ascorbic acid, total phenolic
compounds, and total anthocyanins in arils than the untreated samples (Mirdehghan et al.,
2007b).
Hot water dips and chilling induced decay in plum and decreased ethylene production
while increasing PA levels during subsequent storage at 0 ◦ C (Abu-Kpawoh et al., 2002).
Put infiltration of four different plum varieties delayed ripening and extended shelf life at

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