Iodine Accumulation and Tolerance in Sweet Basil (Ocimum basilicum L.) With Green or Purple Leaves Grown in Floating System Technique

Abstract

Iodine deficiency is a serious worldwide public health problem, as it is responsible for mental retardation and other diseases. The use of iodine-biofortified vegetables represents a strategic alternative to iodine enriched salt for people with a low sodium diet. However, at high concentrations iodine can be toxic to plants. Therefore, research on plant iodine toxicity is fundamental for the development of appropriate biofortification protocols. In this work, we compared two cultivars of sweet basil (Ocimum basilicum L.) with different iodine tolerance: "Tigullio," less tolerant, with green leaves, and "Red Rubin," more tolerant and with purple leaves. Four greenhouse hydroponic experiments were conducted in spring and in summer with different concentrations of iodine in the nutrient solution (0.1, 10, 50, 100, and 200 μM), supplied as potassium iodide (KI) or potassium iodate (KIO 3). Plant growth was not affected either by 10 μM KI or by 100 μM KIO 3 , while KI concentrations higher than 50 μM significantly reduced leaf area, total plant dry matter and plant height. The severity of symptoms increased with time depending on the cultivar and the form of iodine applied. Growth inhibition by toxic iodine concentrations was more severe in "Tigullio" than in "Red Rubin," and KI was much more phytotoxic than KIO 3. Leaf iodine concentration increased with the iodine concentration in the nutrient solution in both varieties, while the total antioxidant power was generally higher in the purple variety. In both basil cultivars, a strong negative correlation was found between the photosynthesis and the leaf iodine content, with significant differences between the regression lines for "Tigullio" and "Red Rubin." In conclusion, the greater tolerance to iodine of the "Red Rubin" variety was associated with the ability to withstand higher concentrations of iodine in leaf tissues, rather than to a reduced accumulation of this element in the leaves. The high phenolic content of "Red Rubin" could contribute to the iodine tolerance of this purple cultivar.

Iodine Biofortification of Apples and Pears in an Orchard Using Foliar Sprays of Different Composition

“…Spraying with I-containing fertilizers caused leaf necroses on apple and pear trees, which increased with increasing I doses ( Figures 6 , 7 ). Similar damage was previously observed in different plant species ( Caffagni et al, 2011 ; Kato et al, 2013 ; Kiferle et al, 2013 ; Cakmak et al, 2017 ; Incrocci et al, 2019 ; Budke et al, 2020a , b ). At equal concentrations I – usually causes stronger phytotoxic effects than IO 3 – .…”

Evidences for a nutritional role of iodine in plants

“…Iodine likely has an indirect effect on plant resistance given that iodine treatments induce the biosynthesis of several enzymatic or non-enzymatic compounds involved in the plant response to environmental stresses (Leyva et al, 2011;Blasco et al, 2013;Gupta, Bajpai, Majumdar & Mishra, 2015). The antioxidant response induced by increasing KI and KIO3 levels was found to be strongly associated with the synthesis of phenolic compounds (Incrocci et al, 2019;Kiferle et al, 2019), in agreement with our transcriptomic data (Figure 4, Table S8). Iodine treatments have also been associated with the modulation of the essential oil composition in basil plants (Kiferle et al, 2019), which plays a key role in defensive and attraction mechanisms in response to the environment (Lee & Ding, 2016).…”

“…The use of low concentrations of iodine is often associated with beneficial effects on plant growth and production, whereas toxic effects are observed when applying iodine at high concentrations, especially in the Iform, which is more phytotoxic than iodate (IO3 -) (Medrano-Macías et al, 2016;Gonzali et al, 2017;Incrocci et al, 2019). Thresholds for beneficial or toxic concentrations have been reported for all micro-nutrients (Welch & Shuman, 1995).…”

New Aspects of Uptake and Metabolism of Non-organic and Organic Iodine Compounds—The Role of Vanadium and Plant-Derived Thyroid Hormone Analogs in Lettuce

“…They were conducted with the aim to prepare an I deficiency prevention program, other than through the consumption of kitchen salt based on plant enrichment with I (White and Broadley, 2009). Among the papers published within the last 15 years, there has been research on species such as kohlrabi (Golob et al, 2020), strawberry (Budke et al, 2020), lettuce (Blasco et al, 2008;Dávila-Rangel et al, 2020), basil (Incrocci et al, 2019;Kiferle et al, 2019), green bean, lettuce (Dobosy et al, 2020), cabbage, cowpea (Ojok et al, 2019), broccoli raab, curly kale, mizuna, and red mustard (Gonnella et al, 2019).…”