preprints.org > biology and life sciences > biochemistry and molecular biology > 202106.0641.v2

Working Paper Article Version 2 This version is not peer-reviewed

Version 1 : Received: 25 June 2021 / Approved: 28 June 2021 / Online: 28 June 2021 (11:22:45 CEST)
Version 2 : Received: 28 September 2021 / Approved: 29 September 2021 / Online: 29 September 2021 (16:24:30 CEST)

Tomato (Solanum lycopersicum), an important vegetable crop, is a host for numerous pests and pathogens. Consequently, tomato breeders are striving to improve pest resistance. Many acces-sions of the wild relative S. habrochaites display high resistance towards arthropod pests such as spider mites and whiteflies and the presence of the sesquiterpene hydrocarbon 7-epi zingiberene in its trichomes has been associated with arthropod resistance. Consequently, tomato breeders are attempting to introgress 7-epi zingiberene from wild to cultivated tomato, which requires the ability to quantify zingiberene. 7-Epi zingiberene has conjugated double bonds causing it to ab-sorb uv light. In fact, de Freitas, et al. [1] have claimed that measurement of absorbance at 270 nm of tomato leaflet washes can be used to quantify zingiberene. However, this claim has never been critically evaluated. We initially evaluated the use of uv absorbance to estimate zingiberene content of leaflet washes from an interspecific hybrid tomato BC4F2 generation that was segre-gating widely for presence and abundance of zingiberene. When absorbances at 270 nm were compared with zingiberene measured by gas chromatography the resulting relationship did not obey the Beer-Lambert law. Consequently, we examined in detail aspects of the uv-absorbance of zingiberenoids by: 1) obtaining uv absorbance spectra for three isolated zingiberenoids and de-termining the relationship between the abundance of each isolated compound and absorbance at single wavelengths; 2) obtaining uv absorbance spectra of leaflet washes of relevant wild acces-sions and parents; 3) obtaining average absorbance spectra for interspecific generations of tomato that were segregating for abundance of zingiberenoids and determining their λmax values in the 250-280 nm region; 4) evaluating by regression the relationship between absorbance at a single wavelength and the concentration of zingiberene and when present, its derivatives, as measured by gas chromatography in several interspecific hybrid generations; and 5) exploring the potential use of absorbances at multiple wavelengths to improve estimates of concentrations of zingi-berenoids. Results indicated that isolated zingiberenoids as well as leaflet washes of wild tomatoes that contain zingiberenoids have broad absorbance spectra in the uv region with a λmax of 264 nm. The relationship between abundance of isolated zingiberenoids and absorbance at a single wavelength of 264 nm did obey the Beer-Lambert Law. Average absorbance spectra for leaflet washes from BC3F5 generation plants sampled by two methods, as well as from a BC5F1 and a BC3F3 generation showed subtle shifts in the λmax away from 264 nm. Furthermore, the rela-tionship between absorbance at 264 nm and zingiberenoid content of these generations did not obey the Beer-Lambert Law in that in each case regression of absorbance on zingiberenoid content of the leaflet washes resulted in non-zero intercept estimates that varied considerably among generations and sampling methods. Use of multiple wavelengths for estimation zingiberenoids in these breeding generations was explored and inclusion of additional absorbances at one or two wavelengths identified by stepwise regression always improved estimates of zingiberenoid content from absorbance data. However, the identified wavelength(s) differed among generations. Taken together the results indicate that measurement of absorbance of tomato leaflet washes at a single wavelength is not a reliable quantitative estimate of zingiberenoids in the leaflet wash. These estimates can be improved by utilizing absorbance at multiple wavelengths, but the par-ticular wavelengths will likely vary among generations. Lastly, measurement of absorbance may be a useful tool in identifying those relatively rare individuals in a generation that is widely segregating for zingiberenoid content. However, even in this situation the determination of the actual zingiberene content e.g., for comparison with the donor parent, would need to be back-stopped by a valid quantitative method such as gas chromatography.

tomato; 7-epi-zingiberene; 9-hydroxy-zingiberene; 9-hydroxy-10,11-epoxy zingiberene; spectrophotometer; absorbance; introgression; breeding; wild relatives

Biology and Life Sciences, Biochemistry and Molecular Biology

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