Exposure of Brassica to Red Light Antagonizes Low Production of Indole-3-Acetic Acid in Leaf Through Root Signaling Under Stress Conditions.

Abstract

Plant leaf is highly sensitive to various growth-promoting and growth-restraining components. This sensitivity is normally caused by the alteration of different phytohormones (predominately by indole-3-acetic acid (IAA)), when the plants exposed to certain environmental conditions. We exposed the hydroponically grown Brassica campestris seedlings (7 days old) to red and green light in order to observe its effect on IAA secretion at leaf. The evaluated data showed that red light antagonized the low production of IAA in leaf by initiating the root signaling through the flavonoid production and high redox activity. The study also explored the link between the differential phytohormonal response and biotic or abiotic stress elimination in leaf through root signaling under green or red light. The results exhibited that the biotic (Pseudomonas syringae or Frankia alni) or abiotic stresses (100 mm AgNO3 or 100 mm tert-butyl alcohol) inhibited flavonoids at the roots and resisted the restoration of IAA at the leaf. However, under green light where IAA was not inhibited, the stresses could not produce flavonoid at the root and further passing the signals to leaf. The results concluded that the growth and photosynthetic rates of the seedlings were improved under red light exposure through flavonoid inducing stresses.