Exogenous treatment with jasmonates (JA) has been shown to reduce the levels of polyamines in many plants. But the role of endogenous JA on polyamine biosynthesis or other cellular metabolites has thus far remained uninvestigated. We developed transgenic tomato (Solanum lycopersicum L.) having severely reduced methyl JA levels by silencing a fruit ripening-associated lipoxygenase (LOX), SlLoxB, using a truncated LOX gene under the control of the constitutive CaMV35S promoter. The LOX suppressed and MeJA-deficient fruits had lowered polyamine levels. Thus, these transgenic fruits were used as a plant model to evaluate the effects of reduced endogenous MeJA on cellular metabolites in ripening tomato fruits using NMR spectroscopy. During on-shelf ripening, transgenic fruits were significantly reduced in the content of 19 out of 30 metabolites examined, including Ile, Val, Ala, Thr, Asn Tyr, Glu, Gln, His, Phe, Trp, GABA, citrate, succinate, myo-inositol, unidentified compound B, nucleic acid compound Nucl1, choline, and trigonelline as compared to the wild-type azygous counterparts. A significant increase in β-glucose levels in transgenic fruits was observed at the pink stage. The transgenic fruits were equivalent to the wild type in lycopene level and chlorophyll degradation rates. Taken together, these results show that intracellular MeJA significantly regulates overall primary metabolism, especially aminome (amino acids and polyamines) of ripening fruits.

A 94-kD protein that accumulates predominately in tomato (Lycopersicon esculenfum) fruit during ripening was purified, and antibodies specific for the purified protein were used to isolate cDNA clones from a red-ripe fruit cDNA library. A sequence analysis of these cDNAs and cross-reactivity of the 94-kD-specific antibodies to the soybean lipoxygenase (LOX) L-1, L-2, and L-3 proteins and soybean LOX L-l-specific antibodies to the 94-kD protein identified it as a member of the LOX gene family. Maximum levels of the 94-kD LOX mRNA and protein are present in breaker to ripe and red-ripe stages, respectively. Expression of 94-kD LOX in different tissues from mature green and red-ripe tomato fruits was found to be greatest in the radial walls of ripe fruit, but immunocytolocalization using tissue printing suggests that the highest accumulation of its protein occurs in locular jelly. None of 94-kD LOX is expressed in nonripening mutant fruits of any age. Never-ripe mutant fruit accumulate the 94-kD LOX mRNA to levels similar to those obtained in wild-type fruit, but fail to accumulate the 94-kD LOX protein. Collectively, the results show that expression of 94-kD LOX is regulated by the ripening process, and ethylene may play a role in its protein accumulation.

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Transgenic `Rutgers' 37-81^ tomato (Lycopersicon esculentum Mill.) homozygous for a pectin methylesterase (PME) antisense gene, which lowers PME activity and increases levels of soluble solids, was compared to azygous (a segregating line of 37-81^ with 0 copies of the introduced gene) and wild-type `Rutgers' in the field during Summer 1992 and 1993 to determine the effects of the introduced PME antisense gene on tomato plant growth, fruit set, fruit yield, and fruit processing attributes. Fresh and dry weight accumulation in transgenic plants was similar to wild-type `Rutgers' and azygous 37-81^ lines during 1992 and 1993, indicating that the introduced PME antisense gene did not affect biomass accumulation. Transgenic plants showed an increase in fruit number and yield in 1992 compared to wild-type `Rutgers' and azygous 37-81^, but no differences were observed among the three genotypes in 1993. Average fruit weight did not show significant differences among the three genotypes in 1992, but was lower in azygous and transgenic plants than wild-type plants in 1993. Transgenic fruit had higher soluble and total solids and higher pH than control fruit, but shelf life was somewhat shorter in transgenic fruit. Overall, these data indicate that introduction of the PME antisense gene, which improves the processing quality of tomatoes, does not adversely affect fruit yield or vegetative growth of plants.