Knowing your enemy before taking the field: A screening of salt and UV-B treatments to boost the biochemical defences of tomato (Solanum lycopersicum L., 'Moneymaker' cultivar) plantlets in controlled conditions

Plants are commonly exposed to different abiotic stress factors that can threaten their growth and development. Abiotic treatments might be used as a tool to increase the tolerance of plants grown in controlled environments before being transplanted in open fields, but this technique needs a careful choice of the stressor dose. We screened several UV-B radiation doses (1 h, 3 h, 6 h and 8 h per day) and NaCl doses (75 mM, 150 mM, 300 mM), separately, to be employed as preconditioning treatments of tomato plantlets (Solanum lycopersicum L., 'Moneymaker' cultivar) cultivated in a controlled environment. Biometric parameters and antioxidant compounds were quantified in leaves and roots. Our results showed that the application of mild abiotic treatments such as 75 mM NaCl for 14 days or 8 h/day UV-B (18.43 kJ/m2) for 7 days to hydroponically grown tomato plantlets can increase the content of foliar total phenolics and flavonoids without inducing strong impairments in the plant growth and development. Interestingly, this work provides evidence that the UV-B radiation, although perceived only by the above-ground organs of the plants, also induces some morphological and biochemical changes in the root system.