DTA

Dottorato

MARTINELLI, MARCO

etd-02262020-133559

The role of iodine in plant physiology

Istituto di Scienze della Vita

Istituto di Scienze della Vita - AGROBIOSCIENCES

relatore Prof. PERATA, PIERDOMENICO
Membro Prof.ssa GUIDI, LUCIA
Membro Prof. FLAMINI, GUIDO
Membro Prof. MENSUALI, ANNA

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25/05/2020;

parziale

Iodine is the element number 53 in the periodic table and belongs to the class of halogens. Among all the halogens, iodine is preferably employed by living organisms and its role has been evolving together with their evolution: at the very begin of life, bacteria and algae started to use its anionic forms (I-/IO3-) as antioxidant or disinfectant compounds whereas animals, specifically vertebrates, exploited it to produce iodinated organic molecules such as thyroid hormones. Although the function of iodine in human physiology is well characterized, in superior plants its role is still unclear. Plants can absorb different forms of iodine (I-/IO3-/organic iodine/I2) from the soil through the root system or from the air through the stomata and can volatilize it as methyl-iodine (CH3I) through specific halo-methyltransferase returning it to the atmosphere. Furthermore, it is well known that high concentrations of iodine can be toxic for plants whereas several scattered publications demonstrated that its use at micromolar doses can exert positive effects on several plant parameters such as biomass, chlorophyll contents, fruit production and stress resistance. Starting from these observations, the main goal of this work is to characterize the influence of iodine on plant performances, especially trying to clarify its main physiological underlying mechanisms. To summarize, plant phenotype, gene expression and secondary metabolites production were evaluated in plants treated at low concentration of iodine. Moreover, the possible incorporation of iodine in proteins was investigated to demonstrate a specific structural/functional role of the element in plant physiology/biochemistry. The results obtained were interesting and pioneering: the positive effect of low iodine doses on plant performances and secondary metabolites production was confirmed, but above all, a fascinating involvement of this halogen in the regulation of the circadian clock has been hypothesized and the presence of proteins likely containing iodo-amino acids was demonstrated. Specifically, the presence of iodinated proteins was detected in shoot and root of different and phylogenetically distant plants (arabidospsis, wheat, tomato, mays, lettuce) through the use of radioactive iodine (I125) as a tracer. These findings represent an important breakthrough and open a new scenario for the knowledge of the role of iodine in plant physiology. Further work needs to be done to identify those proteins, their functions and to understand the effect of iodination as post translational modification on their activity. This discovery can be considered an important piece of the puzzle on the iodine-plant relationship and needs to be integrated with all the information available to comprehend whether iodine could be crowned as a plant micronutrient.

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