Lettuce (Lactuca sativa L.) is a major food crop within the European Union. The objective of this study was to test the potential nutritional quality of three types of lettuce consumed as salads: Lactuca sativa L. var. longifolia (commonly named Cogollos de Tudela) and two cultivars of Lactuca sativa L. var. capitata (Batavia Rubia Munguía and Maravilla de Verano). Distribution of sugars, proteins, minerals and antioxidant compounds (carotenoids, chlorophylls, phenolics, anthocyanins and ascorbate) between outer and inner leaves was tested. The potential benefits of each variety or cultivar were due to different compounds accumulated in leaves. Cogollos de Tudela showed higher levels of Mg and Ca in both external and internal leaves, and greater concentrations of Mn, chlorophylls and carotenoids in inner leaves than lettuces belonging to the var. capitata. Batavia Rubia Munguía had low quantity of Na and an important amount of K, Mg, Ca, Fe and Zn in outer leaves and it was the cultivar that accumulated the highest quantity of water in both outer and inner leaves. Maravilla de Verano showed the greatest contents of anthocyanins and ascorbate in external leaves. In the three cultivars some of the potentially beneficial compounds appeared in higher levels in the outer than in the inner leaves. Therefore, the complete elimination of the external leaves should be reconsidered when lettuces are consumed as salads or used as food crop for the ‘Fourth Range’ of vegetables.Fermín Morales thanks Gobierno de Aragón (A03 research group) for financial support

The association of Lactuca sativa L. with arbuscular mycorrhizal fungi (AMF) can benefit growth and induce the accumulation of mineral nutrients and antioxidants in leaves. Our objectives were (1) to assess to what extent growing season influence growth and nutritional quality of the green-leaf Batavia Rubia Munguía (BRM) and the red-leaf Maravilla de Verano (MV) lettuce cultivars; (2) to test if the growing season affected the effectiveness of AMF as enhancers of the nutritional quality of the aforementioned cultivars; and (3) to check if inoculation with AMF allows extending the season to cultivate these two lettuce cultivars, without a loss of plant growth or nutritional quality. Results showed that winter was the most favourable growing season for both types of lettuce but mycorrhizal plants cultivated in other seasons different from winter achieved higher or similar shoot biomass than their respective non-inoculated controls in winter. AMF induced the accumulation of Fe, proteins, carotenoids and anthocyanins in both cultivars of lettuce in winter and spring. In summer and autumn, both types of lettuce showed increased levels of anthocyanins when associated with AMF. Mycorrhizal BRM also had enhanced levels of K, sugars and ascorbate in winter and spring as well as increased amounts of Mg and Cu in winter and summer. Mycorrhizal MV had increased quantities of Cu, Zn and sugars in spring and Mn in autumn. After estimating intakes of mineral elements through the consumption of 150 g per day of fresh leaves from mycorrhizal lettuces we may affirm that there would not be toxicological risk according to the Recommended Daily Allowances (RDAs). The application of AMF could allow extending cultivation of lettuce to other periods not appropriate for producing non-mycorrhizal plants

Lettuce (Lactuca sativa L.) is extensively grown and is the most widely used food crop for the called “Fourth Range” of vegetables. Lettuce exhibits healthy properties mainly due to the presence of antioxidant compounds (vitamins C and E, carotenoids, polyphenols) alongside significant fibre content and useful amounts of certain minerals. Lettuce can establish a mutualistic association with arbuscular mycorrhizal fungi (AMF). The establishment of the symbiosis involves a continuous cellular and molecular dialogue between both symbionts, which includes the activation of antioxidant, phenylpropanoid or carotenoid metabolic pathways. The presence of AMF colonizing roots of greenhouse-grown lettuces can induce an accumulation of secondary metabolites, vitamins and minerals in leaves that overcome the dilution effect due to the increased size of mycorrhizal plants. Therefore, AMF would allow the intake of minerals and compounds with antioxidant properties to be enhanced without increasing the consumption of lettuce in the diet. In addition, increased quantities of secondary metabolites may help lettuce plants to withstand biotic and abiotic stresses. Our review discusses the influence exerted by several environmental factors and agronomic practices on the ability of AMF for enhancing the levels of vitamins, nutraceuticals and minerals in leaves of green and red-leaf types of lettuces.