244 P. BISWAS ET AL.
red coloration is not random but a patterned disruption of the normal
ripening. Tomato fruit is composed of distinct tissue types including
pericarp, placenta, septa, and locular gel tissues (Brecht 1987). Loc-
ular gel develops prior to ripening of the pericarp (Kader and Morris
1976). Ripening in mature-green tomatoes is initiated in the locular gel,
proceeds through the placenta to the columella, with the first visible
sign of red (yellow or orange) pigmentation occurring at the blossom
end and then coloration progresses toward the stem end of the fruit
(Yahia and Brecht 2012). It is possible that chilling affects tissues differ-
entially resulting in different ripening behavior of various tissues and
eventually uneven blotchy red color appears. In addition, Jiang et al.
(1999) observed that 1-MCP treated bananas showed uneven skin de-
greening and the authors attributed this to positional differences in the
rate of new synthesis of ethylene binding sites. This may also be true
for tomato.
Molecular studies show that interruption of gene expression involved
in color development results in altered color development in chilled
tomatoes. Lycopene is an intermediate of the carotene biosynthetic
pathway in tomato. Carotenoid formation utilizes the ubiquitous
isoprenoid precursor geranylgeranyl pyrophosphate (GGPP). Two
molecules of GGPP are condensed to form phytoene and this reaction
is catalyzed by phytoene synthase (PSY). Phytoene is then converted
to lycopene in a series of dehydrogenation reactions (Alexander and
Grierson 2002). Lurie et al. (1996) reported that phytoene synthase1
(PSY1), the gene that encodes fruit-specific PSY, was downregulated
during chilling. Bird et al. (1991) observed that downregulation of
PSY1resulted in yellow tomatoes devoid of lycopene. Not only was
the PSY1gene affected, but gene expression of at least three other
enzymes involved in carotenoid biosynthesis (namely carotenoid
isomerase-CRTISO, geranylgeranyl diphosphate synthase-2-GGPPS2,
and 1-deoxy-D-xylulose-5-phosphate synthase-DXS) were downregu-
lated in chilled tomatoes (Rugkong et al. 2011). Cruz-Mend ́ıvil et al.
(2015) attributed downregulation of CRTISO to enhanced chilling
susceptibility; meanwhile, upregulation of twoPSY genes was cor-
related with chilling tolerance after a hot water treatment. Rugkong
et al. (2011) further indicated that downregulation of a MADS-box
transcription factor,LeMADS-RIN(responsible for conferring the non-
ripening phenotype of therinmutant and necessary for fruit ripening)
was downregulated after 4 weeks chilling at 3◦C and this reduced
expression contributed to the chilling-induced delayed ripening.
While reduction in expression of carotenoid synthesis genes during
cool storage results in altered red color development in chill-induced