--- title: "5.5.1. Intensity" canonical: "https://wiki.groenkennisnet.nl/space/CPC/11993601/5.5.1.%20Intensity" format: markdown --- Generally, an increase of light intensity leads to more carbohydrates, although there is a clear maximum for photosynthesis. Excessive amounts of light are associated with damages in photosynthetic system II and photoinhibition which result in excessive amounts of energy that cannot be channelled through the biosynthetic processes (Ksas *et al.* 2015). These increases in energy often lead to adaptation and defence. High light can lead to more damage and ROS; therefore, the cell is preparing itself for this by elevating the concentration of secondary metabolites/phytonutrients including carotenoids, tocopherols and plastoquinones that have a role in defence and quenching high-light induced reactive oxygen species (ROS) (Havaux 2005; Krieger-Liszkay 2006). The biosynthesis of carotenoids is upregulated by light (DellaPenna and Pogson 2006; Wurtzel 2018). The expression of several carotenogenic genes, such as lycopene β cyclase (LCYB), and phytoene synthase (PSY) is induced by white light (Gautier *et al.* 2008; Pizarro and Stange 2009). Increasing light intensity between 330 and 440 mmol m2 -1 boosts carotenoids, total phenols, and total antioxidantactivity in various Brassica microgreens. There is an optimal value though, above these limits, it has negative implications (Samuoliene *et al.* 2013; Craver *et al.* 2017). In Spinach and kale leaves, light intensity also affects carotenoids content. However, conditions needed to maximize carotenoids are species and sometimes even cultivar specific (Lefsrud *et al.* 2008; Li *et al.* 2009). Other antioxidants are also elevated by light intensity. Levels of vitamin C and phenolic compounds (rutin and caffeic acids), are also induced without however affecting the reducing sugars content (Gautier *et al.* 2008). In tomato fruit, vitamin C can be increased by increasing light intensity on tomato fruit (Ntagkas *et al.* 2018), because increased solar energy results in higher rates of sugars and consequently of vitamin C biosynthesis (Lee Seung and A Kade 2000). Anthocyanins level can also be significantly increased by changing light and temperature in bell pepper (Liu *et al.* 2018). In at least some cases, there is evidence that these changes are due to increased activity of biosynthetic enzymes that are involved in their biosynthesis (Gautier *et al.* 2008). Light intensity also influences nitrate levels in leafy vegetables as nitrate reductase activity is induced by high light intensities and under low light high levels of nitrate can be found (Petropoulos *et al.* 2008, 2011). Increasing light intensity has a positive effect on shelf life, extending it by more than a week by increasing light intensity in lettuce (Woltering and Witkowska 2016). Short light treatments prior to harvest, to adapt the plant metabolism after a period of normal growth conditions can also be applied to manipulate phytonutrients. In microgreens, supplementary lighting application of red light for 3 days prior to harvest increased total phenolic, total anthocyanin and ascorbic acid contents, as well as the antioxidant activity (Samuoliene *et al.* 2012; Samuolienė *et al.* 2016). > ℹ️ **References** > ℹ️ Craver JK, Gerovac JR, Lopez RG, Kopsell DA. 2017. Light Intensity and Light Quality from Sole-source Light-emitting Diodes Impact Phytochemical Concentrations within Brassica Microgreens. Journal of the American Society for Horticultural Science 142: 3–12. DOI: 10.21273/JASHS03830-16. > ℹ️ > ℹ️ DellaPenna D, Pogson BJ. 2006. VITAMIN SYNTHESIS IN PLANTS: Tocopherols and Carotenoids. Annual Review of Plant Biology 57: 711–738. DOI: 10.1146/annurev.arplant.56.032604.144301. > ℹ️ > ℹ️ Gautier H, Diakou-Verdin V, Bénard C, et al. 2008. How Does Tomato Quality (Sugar, Acid, and Nutritional Quality) Vary with Ripening Stage, Temperature, and Irradiance? Journal of Agricultural and Food Chemistry 56: 1241–1250. DOI: 10.1021/jf072196t. > ℹ️ > ℹ️ Havaux M. 2005. Vitamin E Protects against Photoinhibition and Photooxidative Stress in Arabidopsis thaliana. THE PLANT CELL ONLINE 17: 3451–3469. DOI: 10.1105/tpc.105.037036. > ℹ️ > ℹ️ Krieger-Liszkay A. 2006. Tocopherol is the scavenger of singlet oxygen produced by the triplet states of chlorophyll in the PSII reaction centre. Journal of Experimental Botany 57: 1677–1684. DOI: 10.1093/jxb/erl002. > ℹ️ > ℹ️ Ksas B, Becuwe N, Chevalier A, Havaux M. 2015. Plant tolerance to excess light energy and photooxidative damage relies on plastoquinone biosynthesis. Scientific Reports 5: 10919. DOI: 10.1038/srep10919. > ℹ️ > ℹ️ Lee Seung K, A Kade A. 2000. Pre-harvest and postharvest factors influencing vitamin C content of horticultural crops. Postharvest biology and technology 20: 207–220. DOI: 10.1016/S0925-5214(00)00133-2. > ℹ️ > ℹ️ Lefsrud MG, Kopsell DA, Sams CE. 2008. Irradiance from distinct wavelength light-emitting diodes affect secondary metabolites in kale. HortScience 43: 2243–2244. DOI: 10.1016/j.arcped.2006.03.077. > ℹ️ > ℹ️ Li Q, Kubota C. 2009. Effects of supplemental light quality on growth and phytochemicals of baby leaf lettuce. Environmental and Experimental Botany 67: 59–64. DOI: 10.1016/j.envexpbot.2009.06.011. > ℹ️ > ℹ️ Liu Y, Tikunov Y, Schouten RE, Marcelis LFM, Visser RGF, Bovy A. 2018. Anthocyanin Biosynthesis and Degradation Mechanisms in Solanaceous Vegetables: A Review. Frontiers in Chemistry 6: 2895–2905. DOI: 10.3389/fchem.2018.00052. > ℹ️ > ℹ️ Ntagkas N, Woltering EJ, Marcelis LFM. 2018. Light regulates ascorbate in plants: An integrated view on physiology and biochemistry. Environmental and Experimental Botany 147: 271–280. DOI: 10.1016/j.envexpbot.2017.10.009. > ℹ️ > ℹ️ Petropoulos SA, Constantopoulou E, Karapanos I, Akoumianakis CA, Passam HC. 2011. Diurnal variation in the nitrate content of parsley foliage. International Journal of Plant Production 5: 431–438. > ℹ️ > ℹ️ Petropoulos SA, Olympios CM, Passam HC. 2008. The effect of nitrogen fertilization on plant growth and the nitrate content of leaves and roots of parsley in the Mediterranean region. Scientia Horticulturae 118: 255–259. DOI: 10.1016/j.scienta.2008.05.038. > ℹ️ > ℹ️ Pizarro L, Stange C. 2009. Light-dependent regulation of carotenoid biosynthesis in plants. Ciencia e investigación agraria 36. DOI: 10.4067/S0718-16202009000200001. > ℹ️ > ℹ️ Samuoliene G, Brazaityte A, Jankauskiene J, et al. 2013. LED irradiance level affects growth and nutritional quality of Brassica microgreens. Central European Journal of Biology 8: 1241–1249. DOI: 10.2478/s11535-013-0246-1. > ℹ️ > ℹ️ Samuolienė G, Brazaitytė A, Viršilė A, Jankauskienė J, Sakalauskienė S, Duchovskis P. 2016. Red Light-Dose or Wavelength-Dependent Photoresponse of Antioxidants in Herb Microgreens (J Chamani, Ed.). PLOS ONE 11: e0163405. DOI: 10.1371/journal.pone.0163405. > ℹ️ > ℹ️ Samuoliene G, Sirtautas R, Brazaityte A, Duchovskis P. 2012. LED lighting and seasonality effects antioxidant properties of baby leaf lettuce. Food Chemistry 134: 1494–1499. DOI: 10.1016/j.foodchem.2012.03.061. > ℹ️ > ℹ️ Woltering EJ, Witkowska IM. 2016. Effects of pre-and postharvest lighting on quality and shelf life of fresh-cut lettuce. Acta Horticulturae 1134: 357–365. DOI: 10.17660/ActaHortic.2016.1134.47. > ℹ️ > ℹ️ Wurtzel ET. 2018. Changing form and function through carotenoids and synthetic biology. Plant Physiology: pp.01122.2018. DOI: 10.1104/pp.18.01122.