The levels of endogenous polyamines have been shown to increase in plant cells challenged with low temperature; however, the functions of polyamines in the regulation of cold stress responses are unknown. Here, we show that the accumulation of putrescine under cold stress is essential for proper cold acclimation and survival at freezing temperatures because Arabidopsis (Arabidopsis thaliana) mutants defective in putrescine biosynthesis (adc1, adc2) display reduced freezing tolerance compared to wild-type plants. Genes ADC1 and ADC2 show different transcriptional profiles upon cold treatment; however, they show similar and redundant contributions to cold responses in terms of putrescine accumulation kinetics and freezing sensitivity. Our data also demonstrate that detrimental consequences of putrescine depletion during cold stress are due, at least in part, to alterations in the levels of abscisic acid (ABA). Reduced expression of NCED3, a key gene involved in ABA biosynthesis, and down-regulation of ABA-regulated genes are detected in both adc1 and adc2 mutant plants under cold stress. Complementation analysis of adc mutants with ABA and reciprocal complementation tests of the aba2-3 mutant with putrescine support the conclusion that putrescine controls the levels of ABA in response to low temperature by modulating ABA biosynthesis and gene expression.

In recent years, climate change has altered many ecosystems due to a combination of frequent droughts, irregular precipitation, increasingly salinized areas and high temperatures. These environmental changes have also caused a decline in crop yield worldwide. Therefore, there is an urgent need to fully understand the plant responses to abiotic stress and to apply the acquired knowledge to improve stress tolerance in crop plants. The accumulation of polyamines (PAs) in response to many abiotic stresses is one of the most remarkable plant metabolic responses. In this review, we provide an update about the most significant achievements improving plant tolerance to drought, salinity, low and high temperature stresses by exogenous application of PAs or genetic manipulation of endogenous PA levels. We also provide some clues about possible mechanisms underlying PA functions, as well as known cross-talks with other stress signaling pathways. Finally, we discuss about the possible use of PAs for seed priming to induce abiotic stress tolerance in agricultural valuable crop plants.

Plant growth is influenced by genetic factors and environmental cues. Genotype-by-environment interactions are governed by complex genetic epistatic networks that are subject to natural selection. Here we describe a novel epistatic interaction modulating growth in response to temperature common to 2 Arabidopsis recombinant inbred line (RIL) populations (L er × Kas-2 and L er × Kond). At 14 °C, lines with specific allele combinations at interacting loci (incompatible interactions) have severe growth defects. These lines exhibit deregulated cell death programs and enhanced disease resistance. At 20 °C, growth defects are suppressed, but a positive trait of enhanced resistance is retained. Mapping of 1 interacting QTL to a cluster of RPP1 -like TIR-NB-LRR genes on chromosome 3 is consistent with our finding that environmentally conditioned epistasis depends on activation of the salicylic acid (SA) stress signaling pathway. The nature of the epistatic interaction conforms to the Dobzhansky-Muller model of genetic incompatibility with incomplete penetrance for reproductive isolation. Variation in fitness of different incompatible lines reveals the presence of additional modifiers in the genetic background. We propose that certain interacting loci lead to an optimal balance between growth and resistance to pathogens by modulating SA signaling under specific environments. This could allow the accumulation of additional incompatibilities before reaching complete reproductive isolation.