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

  • ️Tue Jan 01 2019

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

Luca Incrocci et al. Front Plant Sci. 2019.

Abstract

Iodine deficiency is a serious world-wide 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 (KIO3). Plant growth was not affected either by 10 μM KI or by 100 μM KIO3, 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 KIO3. 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.

Keywords: anthocyanic variant; hydroponic system; iodine toxicity; leaf antioxidant capacity; leaf gas exchanges; plant mineral nutrition.

Copyright © 2019 Incrocci, Carmassi, Maggini, Poli, Saidov, Tamburini, Kiferle, Perata and Pardossi.

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Figures

Figure 1
Figure 1

Symptoms of iodine toxicity in sweet basil (Ocimum basilicum L., cultivar “Tigullio”) grown hydroponically for 14 days from 9th to 23rd May 2016 (Experiment 3) with 200 μM KI in the nutrient solution. (A and B) general chlorosis and yellow interveinal patches three days after the onset of iodine treatment. (C) after one week of iodine treatment brown necrotic spots of basal leaves after seven days. (D and E): severe leaf chlorosis and necrosis, and leaf drop after 14 days.

Figure 2
Figure 2

Effect of increasing concentrations of potassium iodide (KI; control = 0.1 μM) or potassium iodate (KIO3) in the nutrient solution on the growth of two cultivars (“Tigullio,” top and “Red Rubin,” bottom) of sweet basil (Ocimum basilicum L.). For each cultivar and each iodine concentration, both the aerial part and the root system of the plants at the end of the experiment are shown. Plants were grown in floating system for 14 days, from 9th to 23rd May 2016 (Experiment 3).

Figure 3
Figure 3

Influence of different concentration of potassium iodide (KI; control = 0.1 μM) or potassium iodate (KIO3) in the nutrient solution on the iodine concentration in the leaf tissues of two cultivars (“Tigullio” and “Red Rubin”) of sweet basil (Ocimum basilicum L.). Each value is the mean (± SD) of three replicates. The linear regression lines for the KI treatments are reported along with the equations for both varieties. For the KIO3 treatments, only the result of the regression analysis of the pooled data of both cultivars is reported, since the individual slopes and intercepts for each cultivar are not significantly different (P < 0.05). Plants were grown hydroponically under greenhouse conditions for 14 days from 9th to 23rd May 2016 (Experiment 3).

Figure 4
Figure 4

Influence of different concentrations of potassium iodide (KI; control = 0.1 μM) or potassium iodate KIO3 in the nutrient solution on net assimilation (A), stomatal conductance (Gs), internal CO2 concentration (Ci) and iodine content of basal leaves of two cultivars (“Tigullio” and “Red Rubin”) of sweet basil (Ocimum basilicum L.). The measurements were taken on the opposite leaves of the 2nd node, at the end of the experimental period. Each value is the mean of three replicates (± S.D.); bars with the same letter indicate values that are not significantly different (P < 0.05). Plants were grown hydroponically under greenhouse conditions for 12 days from 9th to 21st May 2016 (Experiment 4).

Figure 5
Figure 5

Linear regression between the net assimilation (A) and iodine in the basal leaves of two cultivars (“Tigullio” and “Red Rubin”) of sweet basil (Ocimum basilicum L.) grown hydroponically with different concentrations of potassium iodide (KI; control = 0.1 μM) or potassium iodate (KIO3) in the nutrient solution. The measurements were taken on the opposite leaves of the 2nd node at the end of the experimental period. Plants were grown hydroponically under greenhouse conditions for 12 days from 9th to 21st May 2016 (Experiment 4).

Figure 6
Figure 6

Influence of the concentration of potassium iodide (KI; control = 0.1 μM) or potassium iodate (KIO3) in the nutrient solution on the concentration of total chlorophylls (A), carotenoids (B), total phenols as gallic acid equivalents (C) and antioxidant capacity (IC50) (D) in the basal leaves of two cultivars (“Tigullio” and “Red Rubin”) of sweet basil (Ocimum basilicum L.). The measurements were taken at the opposite leaves of the 2nd node at the end of the experimental period. Each value is the mean of four replicates (± SD); bars with the same letter indicate values that are not significantly different (P < 0.05). Plants were grown hydroponically under greenhouse conditions for 12 days from 9th to 21st May 2016 (Experiment 4).

Figure 7
Figure 7

Influence of different concentrations of potassium iodide (KI; control = 0.1 μM) or potassium iodate (KIO3) in the nutrient solution on the cumulated water uptake (expressed per plant or on leaf area basis) of two cultivars (“Tigullio” and “Red Rubin”) of sweet basil (Ocimum basilicum L.). Each bar is the mean (± SD) of four replicates; bars with the same letter indicate values that are not significantly different (P < 0.05). Plants were grown hydroponically under greenhouse conditions for 12 days from 9th to 21st May 2016 (Experiment 4).

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