Ethylene-Nitric Oxide Interplay During Selenium-induced Lateral Root Emergence in Arabidopsis

Selenium (Se) results in primary root shortening and the concomitant induction of lateral roots (LRs) (stress-induced morphogenic response, SIMR). Both ethylene (ET) and nitric oxide (NO) are gasotransmitters interacting with each other during plant growth regulation; however, their involvement and interplay in LR growth have not been examined so far. This study investigates the effect of Se on ET and NO levels and interaction in wild-type (WT) and ET insensitive etr1-1 Arabidopsis. In WT, Se at 15 µM concentration triggered LR emergence (LRem) and slight ET level elevation but in etr1-1 Se-induced LR inhibition was accompanied by four-fold ET level increase which can be associated with the increased expression of ACS2 and ACS8. Treatment with ACC + Se decreased LRem and NO level in WT, whereas AVG + Se in the etr1-1 plants resulted in enhanced LRem and increased NO level indicating that ET may inhibit both NO formation and LR emergence in Se-stressed Arabidopsis. The expression of NO-associated genes (NR1, NR2, GSNOR1, GLB1, GLB2), however, did not correlate with NO levels. Application of GSNO together with Se resulted in enhanced LR outgrowth both in WT and in etr1-1, whereas this effect could be reversed by a NO scavenger which indicates the positive regulatory role of NO during LR emergence. Moreover, GSNO has a clear inhibitory and cPTIO has an inducing effect on ET levels. These data indicate for the first time that the antagonistic interplay between ET and NO regulates the emergence of lateral roots in Arabidopsis under Se stress.