Differential Response of First-Order Lateral Root Elongation to Low Potassium Involves Nitric Oxide in Two Tobacco Cultivars

Abstract

Potassium (K+) is a major limiting element of plant growth, and crops often suffer from low-K+ (LK) stress. Although nitric oxide (NO) is a signaling molecule involved in plant root adaptation to the environment, it remains unclear whether it participates in root growth regulated by LK conditions. Two tobacco cultivars (Nicotiana tabacum L.) exhibiting variant growth features under LK were used in this study. We investigate the effects of LK on root growth, NO accumulation, nitrate reductase (NR) activity and effects of a NO Donor (SNP and NONOate), NO scavenger (cPTIO), NR inhibitor (tungstate), and NO synthase inhibitor (L-NAME) on elongation of first-order lateral roots (LR). Compared with control treatment, the LK-tolerant cultivar NC89 maintained plant growth under LK at 14 days, whereas the dry weight was reduced significantly in the LK-susceptible cultivar Yunyan1. Low-K+-inhibited root growth, mostly by impairing first-order LR formation and elongation was only recorded in cv. Yunyan1. NO accumulation increased in root tips even when cv. Yunyan1 was subjected to LK at day 1. LK-induced NO was generated by the NR pathway during early LK. Application of SNP and NONOate to control-treated plants decreased first-order LR elongation to levels similar to LK treatment in cv. Yunyan1, whereas cPTIO, L-NAME, and tungstate application had the opposite effect. Further results suggested that NO might be involved in auxin-mediated LR elongating as plants respond to LK. In conclusion, NO generated by the NR pathway may be involved in the inhibition by LK stress of first-order LR elongation in tobacco plants.