Abstract
Plants are often repeatedly exposed to stresses during their lives and have a mechanism called stress imprinting that provides “memories” of stresses they experience and increases their ability to cope with later stresses. To test hypotheses that primed bryophytes can preserve their stress imprinting after 6 days of recovery and induce higher levels of osmolytes and ROS‐scavenging activities upon later stress exposure, and there exist population‐level differentiation in their desiccation defenses, we transplanted samples of two populations of each of two moss species, Hypnum plumaeforme and Pogonatum cirratum, in a nature reserve in southern China. After 16 months of acclimation, sets of each population were subjected to control, one‐time desiccation stress, duplicated desiccation stress and cross‐stress (low temperature stress followed by desiccation stress) treatments. Levels of oxidant enzymes, osmolytes, and phytohormones in the samples were then determined. The desiccation stress generally led to increases in activities or contents of superoxide dismutase, guaiacol peroxidase, catalase, proline, soluble sugars, soluble proteins, and stress hormones including abscisic acid (ABA), jasmonates (JA), and salicylic acid (SA), with differences between both species and populations. After a 6‐day recovery period, contents of phytohormones (including ABA, JA, SA, and cytokinins) in stressed H. plumaeforme had substantially fallen toward control levels. The duplicated and cross‐stress treatments generally led to further accumulation of proline, soluble sugars, and soluble proteins, with further increases in activities of antioxidant enzymes in some cases. Furthermore, significant differences between allochthonous and native populations were found in contents of malondialdehyde and osmolytes, as well as antioxidant enzyme activities. Our results confirm the hypotheses and highlight the importance of osmolytes in mosses' stress responses.
Highlights
Land plants are frequently challenged by diverse environmental stresses as they cannot escape from adverse environments
Gametophytes of each population were planted in 12 trays (30 × 50 cm) assigned to four treatment regimes: con‐ trol (CK), one‐time desiccation stress (OD), duplicated desiccation stress (DD), and cross‐stress
There has been reported that the membrane damage of Fontinalis antipyretica by dehydration is due to nitric oxide end products rather than MDA (Cruz de Carvalho, Catalá, Branquinho, Marques da Silva, & Barreno, 2017), we have found significant increase in MDA in H. plumaeforme and P. cirratum upon exposure to water stress (Liu, Lei, Jin, et al, 2015)
Summary
Land plants are frequently challenged by diverse environmental stresses as they cannot escape from adverse environments. Abscisic acid (ABA), jasmonates (JA), salicylic acid (SA), and ethylene, which are defined as stress phytohormones, generally in‐ crease in stress conditions (Bruce, Matthes, Napier, & Pickett, 2007). Others, such as auxins, gibberellins, and cytokinins, are involved in stress responses via complex signaling networks (Verma et al, 2016; Verslues, 2016). A complicating factor is that populations within a species' distribution are often exposed to different environmental conditions and develop local adapta‐ tions (Briggs, 1972; Chambers & Emery, 2016; Lázaro‐Nogal et al, 2016) As both selective environmental pressures and gene flow limitations drive differentiation, between‐population distances and dispersal potentials both affect the extent of population‐level differentiation (Chambers & Emery, 2016; Korpelainen, Pohjamo, & Laaka‐Lindberg, 2005). We expected to find greater differentiation between the two H. plumaeformae populations than between the two P. cirratum populations, because the latter are geographically closer to each other
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