AUTHOR=Trejo-Téllez Libia Iris , Estrada-Ortiz Elías , Gómez-Merino Fernando Carlos , Becker Christine , Krumbein Angelika , Schwarz Dietmar 

TITLE=Flavonoid, Nitrate and Glucosinolate Concentrations in Brassica Species Are Differentially Affected by Photosynthetically Active Radiation, Phosphate and Phosphite

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00371

DOI=10.3389/fpls.2019.00371

ISSN=1664-462X

ABSTRACT=<p>We evaluated the effects of phosphate (Pi-deficiency: 0.1 mM; Pi-sufficiency: 0.5 mM), phosphite (low-Phi: 0.1 mM; medium-Phi: 0.5 mM; and high-Phi: 2.5 mM), and two mean daily photosynthetically active radiations (lower PAR: 22.2 mol ⋅ m<sup>-2</sup> ⋅ d<sup>-1</sup>; higher PAR: 29.7 mol ⋅ m<sup>-2</sup> ⋅ d<sup>-1</sup>), as well as their interactions, on flavonoid, nitrate and glucosinolate (GL) concentrations and growth characteristics in hydroponically grown <italic>Brassica campestris</italic> cv. Mibuna Early and <italic>Brassica juncea</italic> cv. Red Giant. As expected, higher PAR increased dry matter and contrariwise decreased number of leaves but only in <italic>B. campestris</italic>. Total flavonoid and individual flavonoid compounds increased with the higher PAR value in <italic>B. campestris</italic>. Pi-sufficiency resulted in a lower quercetin concentration in both species, the isorhamnetin and total flavonoid concentrations in <italic>B. campestris</italic>, and the cyanidin concentration in <italic>B. juncea</italic>, in comparison to Pi-deficiency. Similarly, Pi-sufficient plants exhibited lower GL concentration, especially alkyl-GLs in <italic>B. campestris</italic> and alkenyl-GLs and an aryl-GL in <italic>B. juncea</italic>. Pi did not affect the nitrate concentration in either species, and nor did Phi influence the flavonoid concentrations in either species. In <italic>B. campestris</italic>, medium Phi (0.5 mM) increased the 1-methoxyindol-3-ylmethyl GL concentration by 28.3%, as compared to that observed at low Phi. In <italic>B. juncea</italic>, high Phi level increased the but-3-enyl-GL concentration by 18.9%, in comparison to values recorded at medium Phi. <italic>B. campestris</italic> plants exposed to higher PAR increased total flavonoids concentration. In both <italic>Brassica</italic> species, higher PAR stimulated the alkyl-, alkenyl-, and indole-GLs. The interaction of lower PAR and increasing Phi significantly decreased flavonoid concentration in <italic>B. juncea</italic>, whereas increasing Phi at higher PAR increased such concentration in this species. The same combination reduced the concentration of 2-phenylethyl- and indol-3-ylmethyl-GL in <italic>B. juncea</italic>. The highest indol-3-ylmethyl-GL concentration was observed when Pi was deficient combined with medium Phi in <italic>B. juncea</italic>. Thus, PAR, Pi and Phi may modulate flavonoid, GL and nitrate concentrations in <italic>Brassica</italic> species, which may be a useful tool to improve the nutraceutical quality of these leafy vegetables if properly managed.</p>