Abstract:

The role of thiamine (THI)-induced nitric oxide (NO) synthesis in the improvement of tolerance to boron (B) toxicity in pepper (Capsicum annuum L.) was studied. A solution of THI (50 or 100 mg L-1) was sprayed to the foliage of pepper plants exposed to high B regime (2.0 mM H3BO3) once a week for 4 weeks. A scavenger of NO (0.1 mM), cPTIO, along with THI was sprayed once a week to ascertain whether or not endogenous NO played a role in the alleviation of B stress in pepper plants by THI. There were significant reductions in plant dry weight, PSII quantum efficiency (F-v/F-m), total chlorophyll, leaf calcium (Ca2+) and potassium (K+) contents as well as leaf water potential by 47.57%, 28.78%, 34.42%, 45.45%, 55.53%, and 471.4%, respectively, but there was a significant increase in the leaf proline, ascorbate (AsA), glutathione (GSH), hydrogen peroxide, malondialdehyde, electron leakage, B levels and NO by 2.6-, 2.3-, 1.9, 3.7-, 5.6-, 2.2-, 3.6-, and 3.0-fold, respectively in B-stressed plants. Both treatments of TI II mitigated B-induced oxidative damage and led to a further increase in NO synthesis. The positive effect of THI on plants grown under B stress was fully eliminated by the cPTIO application by lowering leaf NO content. These findings exhibit that NO may function as a downstream signal in THI-induced tolerance to B toxicity in pepper plants by reversing oxidative stress, enhancing the antioxidant defense mechanism and sustaining mineral nutrient homeostasis. Thus, NO and THI both contributed to improved B toxicity tolerance in pepper plants.

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