NADPH oxidase AtrbohD an d AtrbohF negatively modulate lateral root development by changing the peroxidase activity and increasing the local generation of superoxide in primary roots of Arabidopsis in an auxin-independent manner. NADPH oxidase subunits AtrbohD and AtrbohF play pivotal roles in regulating growth, development and stress responses in Arabidopsis. However, whether they modulate lateral root (LR) formation has not yet been addressed, and the detailed mechanisms underlying the process remain unanswered. Here, we show that two null double mutants atrbohD1/F1 and atrbohD2/F2, in which both AtrbohD and AtrbohF genes are disrupted, had remarkably higher LR density than wild-type (WT), or the single mutant atrbohD1 and atrbohF1. Compared to WT, the double mutants exhibited early emerged LRs and enhanced density of lateral root primordia (LRP). Unexpectedly, the production of superoxide (O2 (-)), but not hydrogen peroxide, in the mature area of the primary root containing LRs significantly increased in the double mutants relative to that in WT. Further experiments revealed that the local accumulation of O2 (-) led to the enhancement of LR density in the double mutants. Moreover, the deficiency of AtrbohD and AtrbohF caused a marked increase in peroxidase activity in the mature root zone, which contributed to the localized accumulation of O2 (-) and the elevated LR density in the double mutants. Furthermore, the double mutants were not sensitive to exogenous auxin naphthalene acetic acid or auxin transport inhibitor 1-N-naphthylphthalamic acid in terms of LR formation. The auxin response of LRP in vivo in atrbohD1/F1 was also similar to that in WT. Taken together, these results suggest that AtrbohD and AtrbohF negatively modulate LR development by controlling the local generation of superoxide in an auxin-independent manner. These findings provide new insights into the mechanisms of NADPH oxidase-mediated regulation of LR branching in Arabidopsis.

Abscisic acid (ABA) plays pivotal roles in plant growth and development and in responses to diverse stresses. It also modulates the growth of primary and lateral roots. Much evidence indicated that key cellular components auxin, ethylene, PLETHs, reactive oxygen species and Ca are involved in the regulation of ABA suppression of root elongation. In this review, we summary the molecular mechanism for ABA inhibiting primary root growth, focusing on the roles of these components in Arabidopsis.

Plasma membrane NADPH oxidases (NOXs), also named respiratory burst oxidase homologues (Rbohs), are critical generators of reactive oxygen species (ROS), which as signal molecules regulate growth and development, and adaptation to various biotic and abiotic stresses in plants. NOXs-dependent ROS production is frequently induced by diverse phytohormones. The ROS commonly function downstream of, and interplay with hormone signalings, coordinately modulating plant development and stress tolerance. In this review, we summarize recent advances on the roles and molecular mechanisms of Rbohs in mediating signalings of multiple hormones including auxin, gibberellins, abscisic acid, ethylene and brassinosteroids in plants.

Nitric oxide (NO) as an important secondary messager plays crucial roles in modulating stomatal movement, especially abscisic acid (ABA)-induced stomatal closure. Accumulating evidence indicates that NO positively and negatively regulates guard cell ABA signaling. NO is also implicated in stomatal closure mediated by hydrogen sulfide, small peptides, polyamines, and methyl jasmonate. In this review, we summarize recent advances on the roles and the underlying mechanisms of NO in regulating stomatal closure in plants.

Addendum to: Hao FS, Zhao SL, Dong H, Zhang H, Sun LR, Miao C. Nia1 and Nia2 are involved in exogenous salicylic acid-induced nitric oxide generation and stomatal closure in Arabidopsis.