Ultraviolet-B-induced flavonoid accumulation in Betula pendula leaves is dependent upon nitrate reductase-mediated nitric oxide signaling

Abstract

Nitric oxide (NO) is an important signaling molecule involved in many physiological processes in plants. Nitric oxide generation and flavonoid accumulation are two early reactions of plants to ultraviolet-B (UV-B) irradiation. However, the source of UV-B-triggered NO generation and the role of NO in UV-B-induced flavonoid accumulation are not fully understood. In order to evaluate the origin of UV-B-triggered NO generation, we examined the responses of nitrate reductase (NR) activity and the expression levels of NIA1 and NIA2 genes in leaves of Betula pendula Roth (silver birch) seedlings to UV-B irradiation. The data show that UV-B irradiation stimulates NR activity and induces up-regulation of NIA1 but does not affect NIA2 expression during UV-B-triggered NO generation. Pretreatment of the leaves with NR inhibitors tungstate (TUN) and glutamine (Gln) abolishes not only UV-B-triggered NR activities but also UV-B-induced NO generation. Furthermore, application of TUN and Gln suppresses UV-B-induced flavonoid production in the leaves and the suppression of NR inhibitors on UV-B-induced flavonoid production can be reversed by NO via its donor sodium nitroprusside. Together, the data indicate that NIA1 in the leaves of silver birch seedlings is sensitive to UV-B and the UV-B-induced up-regulation of NIA1 may lead to enhancement of NR activity. Furthermore, our results demonstrate that NR is involved in UV-B-triggered NO generation and NR-mediated NO generation is essential for UV-B-induced flavonoid accumulation in silver birch leaves.

Protective Effect of Nitric Oxide (NO) against Oxidative Damage in Larix gmelinii Seedlings under Ultraviolet-B Irradiation

“…This suggested that under the UV-B radiation stress, NOS in Larix gmelinii seedlings leaves could promote the synthesis of NO. This result is in agreement with the results of Ming Zhang et al [38]. SNP treatments were applied under enhanced UV-B radiation.…”

Nitric oxide mediates hypocrellin accumulation induced by fungal elicitor in submerged cultures of Shiraia bambusicola

“…Numerous studies have focused on elicitors for the induction of plant secondary metabolite accumulation and the signal transduction pathway. Zhang et al (2011) demonstrated that NO induces the expression of the flavonoid biosynthetic NIA1 genes, and flavonoid synthesis. SA enhances the accumulation of secondary metabolites and expression of defense genes in Atractylodes lancea DC (Wang et al 2011).…”

“…Quantification of NO by haemoglobin assay NO accumulation was assayed and calculated by following the conversion of oxyhemoglobin (HbO 2 ) to methemoglobin (MetHb) at 401 and 421 nm, using an extinction coefficient of 77 mm -1 cm -1 (A 401 HbO 2 , A 421 MetHb) (Zhang et al 2011). Oxyhemoglobin was prepared as detailed previously .…”

Functional Role of Nitric Oxide Under Abiotic Stress Conditions

“…Zhang et al (2011) have proved that NO derived from NR plays a role in conferring UV-B stress tolerance. Direct association between NR activity, NO emission and nitrite (NO 2 − ) content was determined in silver birch (Betula pendula) under UV-B radiation.…”

“…It was confirmed that NR activity and NO emission are required for flavonoid accumulation in silver birch, and NO scavenger cPTIO abolished NO. Although a role for an NOS-like source for NO during UV-B stress was suggested in maize and G. biloba (Hao et al 2009;Tossi et al 2009a), the effect of mammalian NOS inhibitors on UV-B-induced NO generation cannot be shown by Zhang et al (2011).…”