Author
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Ishida, Betty |
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Submitted to: International Symposium for Natural Colorants
Publication Type: Proceedings Publication Acceptance Date: 4/10/2000 Publication Date: 4/10/2000 Citation: Ishida, B.K. 2000. Lycopene production in tomato calyces. 4th Int'l Symposium for Natural Colorants Proceedings, 4/5/00, p. 127-134. Interpretive Summary: We are interested in finding better ways to control tomato ripening. We have discovered and developed an in-vitro tomato system in our laboratory in which calyces (sepals) of tomato fruit (Lycopersicon esculentum, cv. VFNT Cherry) develop into fruit tissue when cultured at16-22 degress C. Calyces grown at these cooler temperatures swell, lose their green color, and become red and succulent. They produce ethylene and many volatile flavor compounds and sugars that are characteristic of ripe tomato fruit. Lycopene is the compound in tomatoes that makes them red. Recently we found that lycopene concentrations in tomato fruit cultured at these lower temperatures are very high, about ten times higher than in field- and greenhouse-grown tomatoes. A number of volatile flavor compounds also increase. We also found that VFNT Cherry tomato calyces have high tomato AGAMOUS (TAG1) gene expression. The AGAMOUS gene is important in determining organ identity early in flower development. Normally TAG1 is turned on (messenger RNA is expressed) in carpels, which develop into fruit, and stamens, but is not in calyx. TAG1 RNA levels increase as the calyx changes into fruit tissue and ripens. They also increase in ripening tomato fruit. In both tissues, TAG1 expression was correlated with degree of ripening. We therefore believe that TAG1 is involved in changes that result in its ripening and lycopene production. If we can control TAG1 expression in tomato fruit, we might be able to regulate when tomatoes begin to ripen in the field. Technical Abstract: We have discovered and developed an in-vitro tomato system in our laboratory in which calyces (sepals) of tomato fruit (Lycopersicon esculentum, cv. VFNT Cherry) develop into fruit tissue when cultured between 16 and 22 degrees C. Cool temperatures induce calyces to become swollen, lose their green color, and become red and succulent. At the onset of ripening of these calyx tissues, ethylene is produced, followed by ultrastructural changes in cell walls, flavor volatile production, and changes in sugars that are characteristic of ripe fruit. Recently we found that lycopene concentrations in VFNT Cherry tomato fruit cultured in vitro at 16 degrees C are unusually high (580 + 70 micrograms g-1, about ten times higher than in standard field and greenhouse tomatoes). A number of volatile flavor compounds, as well as some that are not directly related, increase with cool-temperature induction. We also found that VFNT Cherry tomato calyces have high tomato AGAMOUS (TAG1) gene expression. The AGAMOUS gene is important in determining meristem and organ identity during the very early stages of flower development. Although our studies were conducted on fully developed calyces, we found that TAG1 RNA levels increase as the calyx is transformed into fruit tissue and ripens. TAG1 RNA concentrations also increase in ripening tomato fruit. In both tissues, TAG1 expression was correlated with degree of ripening. We therefore suggest that TAG1 has an additional role, one involved in fruit ripening and lycopene production. |
