Lycopene Content of Hydroponically Cultivated and Grafted Tomato Varieties

Heirloom tomato varieties are in demand by consumers due to high antioxidant levels. However, these varieties are difficult to produce and are prone to disease and low yield. To overcome these problems, heirloom tomatoes may be grafted onto disease-resistant rootstocks and cultivated in hydroponic systems. However, it is unknown if the lycopene content of hydroponically grown tomatoes is affected by grafting.
Heirloom (Black Krim and Green Zebra) and standard (Big Beef) varieties were grafted onto wild type (WT) or productive rootstocks (Arnold and Supernatural). Tomatoes were harvested at maturity, freeze-dried, ground into a powder, and stored at -20ºC until further analysis. Freeze-dried tomato powder (100 mg) was extracted by 1 mL hexane/acetone/ethanol (2:1:1, v/v/v) under shaking for 30 min at room temperature, after which 0.2 mL ddH2O was added and vigorously mixed. The polar and non-polar phases were separated by centrifugation at 3000 xg for 10 min, after which the non-polar phase containing lycopene was collected. The remaining plant material was extracted once more using 1 mL hexane/acetone/ethanol (2:1:1, v/v/v) as described above. The content of lycopene was determined by measuring the absorbance spectrophotometrically at 503 nm (εlycopene =1.72 × 105 M-1cm-1).
Comparing self-grafted Big Beef, Black Krim, and Green Zebra showed lycopene contents of 9.97±2.02, 15.55±1.97, and 3.37±0.39 mg/kg dry weight (mean±std), respectively. The results were statistically significantly different between the three varieties reflecting the natural pigmentation in each. When comparing the effect of grafting onto non-WT rootstocks, surprisingly, Big Beef grafted onto Supernatural demonstrated significantly higher lycopene content (17.25±0.24 mg/kg dry weight) compared to both WT (9.97±2.02 mg/kg dry weight) and Arnold (8.09±1.39 mg/kg dry weight) rootstocks. Similar effects were not observed for the grafted heirloom varieties, for which the lycopene content was determined to be 15.55±1.97, 16.29±2.93, 19.14±3.21 mg/kg dry weight for Black Krim grafted onto WT, Arnold, and Supernatural, respectively, and 3.37±0.39, 3.52±0.15, 3.03±0.03 mg/kg dry weight for Green Zebra grafted onto WT, Arnold, and Supernatural, respectively.

传家品种的番茄因富含抗氧化物质而深受消费者青睐。然而，此类品种的生产难度较大，且易受病害侵袭，产量较低。为解决这些问题，可通过将传家品种的番茄嫁接于抗病性根砧上，并在水培系统中进行栽培。然而，关于水培种植的番茄中番茄红素含量是否受嫁接影响尚无定论。对黑克里姆和绿斑纹等传家品种（Black Krim 和 Green Zebra）及标准品种（如大牛肉Big Beef）进行嫁接，嫁接对象为野生型（WT）或生产性根砧（Arnold 和 Supernatural）。待番茄成熟后，将其收获、冻干、研磨成粉，并储存于-20°C直至进一步分析。将100毫克的冻干番茄粉用1毫升的己烷/丙酮/乙醇（体积比2:1:1）在室温下振荡提取30分钟，随后加入0.2毫升去离子水并剧烈搅拌。通过3000 xg的离心力分离极性和非极性相，收集含有番茄红素的非极性相。剩余的植物材料再次用1毫升己烷/丙酮/乙醇（体积比2:1:1）提取，方法同上。通过在503纳米处测定吸光度光谱光度法确定番茄红素含量（εlycopene =1.72 × 105 M-1cm-1）。对自嫁接的大牛肉、黑克里姆和绿斑纹进行对比分析，结果显示其干重中的番茄红素含量分别为9.97±2.02、15.55±1.97和3.37±0.39毫克/千克（均值±标准差）。三个品种之间的结果表明了各自自然色素的差异。在比较嫁接到非WT根砧的效果时，令人惊讶的是，与野生型（WT）和Arnold根砧相比，大牛肉嫁接到Supernatural根砧上的番茄红素含量显著增加（17.25±0.24毫克/千克干重）。对于嫁接的传家品种，未观察到类似效果，其嫁接到WT、Arnold和Supernatural根砧上的番茄红素含量分别为15.55±1.97、16.29±2.93和19.14±3.21毫克/千克干重，而绿斑纹嫁接到WT、Arnold和Supernatural根砧上的番茄红素含量分别为3.37±0.39、3.52±0.15和3.03±0.03毫克/千克干重。