Transgenerational effects of stress on reproduction strategy in the mixed mating plant Lamium amplexicaule

Abstract

Background: The theory of Condition Dependent Sex predicts that - everything else being equal - less fit individuals would outcross at higher rates compared with fitter ones. Here we used the mixed mating plant Lamium amplexicaule, capable of producing both self-pollinating closed flowers (CL), alongside open flowers (CH) that allow cross pollination to test it. We investigated the effects of abiotic stress - salt solution irrigation - on the flowering patterns of plants and their offspring. We monitored several flowering and vegetative parameters, including the number and distribution of flowers, CH fraction, and plant size.

Results: We found that stressed plants show an increased tendency for self-pollination and a deficit in floral and vegetative development. However, when parentally primed, stressed plants show a milder response. Un-stressed offspring of stressed parents show reversed responses and exhibit an increased tendency to outcross, and improve floral and vegetative development.

Conclusions: In summary, we found that stress affects the reproduction strategy in the plants that experienced the stress and in subsequent offspring through F2 generation. Our results provide experimental evidence supporting a transgenerational extension to the theories of fitness associate sex and dispersal, where an individual's tendency for sex and dispersal may depend on the stress experienced by its parents.

Keywords: Lamium amplexicaule (henbit); Cleistogamy; Condition dependent sex; Epigenetic inheritance; FAS; Mixed mating; Phenotypic plasticity; Stress; Transgenerational effect.

Fig. 1

(A): L. amplexicaule dimorphic flowers. CL performs self-pollination. CH performs both self and cross pollination. (B): Schematic illustration depicting the experimental regime. Single seed descendants were divided into two groups- one watered with 50 mM NaCl solution (S, red arrow), and the other watered with H2O (C, blue arrow). Seeds collected were divided in the same manner, forming a total of four study groups. Subsequent seeds were all irrigated with H2O. Group names are composed of chronological C or S indicating irrigation type of each generation. Experiment 1 included groups of SSD line 15: plants experiencing ongoing salt stress for one generation (CS), two generations (SS), non-stress F1 offspring (SC), and control (CC). Experiment 2 included groups of SSD line 8: non-stress F1 offspring of one stress generation (CSC), and two stress generations (SSC), non-stress F2 offspring of one stress generation (SCC), and control (CCC). We define the offspring of stressed parents (groups SS, SC, CSC, SSC, and SCC) as stress-primed, and the offspring of unstressed parents (CC, CS, CCC) as unprimed

Fig. 2

(A): Box-plots for CH (chasmogamy) rates. Group means (x). Significance according to Mann- Whitney U test corrected under Benjamini-Hochberg FDR procedure for multiple comparisons, done separately for each SSD line. Each bar is the mean value ± SD. Different letters indicate significant differences among groups. (B): Frequency of CH rate within populations of line 15 (top) and line 8 (bottom). X-axis: CH fraction. Y-axis: frequency in the population

Fig. 3

Schematic illustration depicting the average main stalk of line 15 study groups, proportioned to plant height and number of whorls. The bar plot represents the distribution of flowers upon whorls. Grey: Cleistogamic (CL, closed) flowers. Purple: Chasmogamic (CH, open) flowers. Under stalks is an illustration of the average whorl containment (flowers per whorl). Parentally primed plants (SS, SC) produced more flowers with higher CH rates in the lower whorl positions forming earlier. Group sizes: Line 15: CS n = 32, SS n = 32, SC n = 31, and CC n = 31. Line 8: CSC n = 32, SSC n = 30, SCC n = 32, and CCC n = 23

Fig. 4

Box-plots for (A): number of flowers, (B): plant height, (C): number of flowers per whorl. Group means (x). Significance according to Mann- Whitney U test corrected under Benjamini- Hochberg FDR procedure for multiple comparison, done separately for each SSD line. Each bar is the mean value ± SD. Different letters indicate significant differences among groups