Putrescine Depletion Affects Arabidopsis Root Meristem Size by Modulating Auxin and Cytokinin Signaling and ROS Accumulation.

Ahmed M Hashem,Yanni Feng,Qing Zhao,Keith Lindsey,Shangjian Chen,Jennifer F Topping,Simon Moore,Junli Liu,Chenchen Hu,Chunli Chen,Ibrahim Eid Elesawi

doi:10.3390/ijms22084094

Abstract

Polyamines (PAs) dramatically affect root architecture and development, mainly by unknown mechanisms; however, accumulating evidence points to hormone signaling and reactive oxygen species (ROS) as candidate mechanisms. To test this hypothesis, PA levels were modified by progressively reducing ADC1/2 activity and Put levels, and then changes in root meristematic zone (MZ) size, ROS, and auxin and cytokinin (CK) signaling were investigated. Decreasing putrescine resulted in an interesting inverted-U-trend in primary root growth and a similar trend in MZ size, and differential changes in putrescine (Put), spermidine (Spd), and combined spermine (Spm) plus thermospermine (Tspm) levels. At low Put concentrations, ROS accumulation increased coincidently with decreasing MZ size, and treatment with ROS scavenger KI partially rescued this phenotype. Analysis of double AtrbohD/F loss-of-function mutants indicated that NADPH oxidases were not involved in H2O2 accumulation and that elevated ROS levels were due to changes in PA back-conversion, terminal catabolism, PA ROS scavenging, or another pathway. Decreasing Put resulted in a non-linear trend in auxin signaling, whereas CK signaling decreased, re-balancing auxin and CK signaling. Different levels of Put modulated the expression of PIN1 and PIN2 auxin transporters, indicating changes to auxin distribution. These data strongly suggest that PAs modulate MZ size through both hormone signaling and ROS accumulation in Arabidopsis.

Highlights

Polyamines (PAs) are small polycationic compounds found in all living organisms.Due to their characteristic positive charges, they can interact with negatively charged molecules such as DNA, RNA, proteins, and phospholipids, and influence their activity [1]
The results suggested that ADC2 activity is higher in the root than that of ADC1, since while D-Arg treatment inhibited root length in WT, adc1, and adc2, DArg inhibition of ADC1 activity in the adc2 mutant resulted in a shorter root than inhibition of ADC2 did in the adc1 mutant, indicating that the adc2 mutant root phenotype is more sensitive to D-Arg than adc1 (Figure 1B,C)
We explored changes in reactive oxygen species (ROS) accumulation and hormone signaling under conditions of ADC1/2 inhibition and

Summary

Introduction

Polyamines (PAs) are small polycationic compounds found in all living organisms. Due to their characteristic positive charges, they can interact with negatively charged molecules such as DNA, RNA, proteins, and phospholipids, and influence their activity [1]. PAs have been shown to be implicated in the regulation of several plant physiological processes, including flower development, embryogenesis, organogenesis, senescence, and fruit maturation and development [4], and are involved in Arabidopsis meristem development [5]. Recent studies on plant polyamines have been reviewed [9]. Put is the central diamine substrate compound for the biosynthesis of higher triamine and tetraamine polyamines.

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