Minerals

The role of minerals in plant foods that have a positive effect on human health are well established (Lachance 1998). Tomato mineral composition is greatly influenced by plant nutrition, and as a result, has been well characterized in the context of mineral deficiency and the effect of these conditions on plant health. There is significant genotypic variation for mineral content in tomato fruit. Potassium, together with nitrate and phosphorous, constitutes approximately 93% of the total inorganic fruit constituents (Hobson and Davies 1971). The concentration of other minerals in the fruit is low. Hobson and Davies (1971) summarize prior reviews of tomato mineral composition.

Phosphorous levels in 25 divergent tomato accessions ranged from 3.1 to 6.7 mM (Paulson and Stevens 1974). Stevens and Paulson (1973) reported a strong genotype-environment interaction for fruit phosphorous concentration that was not attributed to variation in available soil phosphorous. The study suggested that few genes are involved in genetic control of fruit phosphorous levels and that additive and dominance effects, in addition to epistatic interactions, contribute to observed phenotypes.

Stevens (1972) reported potassium concentrations that ranged from 45.2 to 86.7meq/liter among 55 divergent tomato lines. Potassium deficiency may contribute to poor fruit color and reduced acid content (Bradley 1946; Carangal et al. 1954). Positive correlations between potassium content and titratable acidity have been reported (Hobson and Davies 1971).

Heritable differences for calcium utilization efficiency in tomato have been documented (Giordano et al. 1982). The potential to manipulate mineral composition in tomato using transgene approaches is well demonstrated by a recent report wherein calcium content was increased up to 50% in carrot via expression of an Arabidopsis H+/Ca2+ transporter (Park et al.

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