Quantifying spatial heterogeneity of chlorophyll fluorescence during plant growth and in response to water stress

Plant Methods 2015

Justine Bresson, François Vasseur, Myriam Dauzat, Garance Koch, Christine Granier, Denis Vile

We developed a method to quantify the dynamics of spatial heterogeneity of photosynthetic efficiency through the distribution-based analysis of Fv/Fm values. The method was applied to Arabidopsis thaliana grown under well-watered and severe water deficit (survival rate of 40%). First, whole-plant Fv/Fm shifted from unimodal to bimodal distributions during plant development despite a constant mean Fv/Fm under well-watered conditions. The establishment of a bimodal distribution of Fv/Fm reflects the occurrence of two types of leaf regions with contrasted photosynthetic efficiency. The distance between the two modes (called S) quantified the whole-plant photosynthetic heterogeneity. The weighted contribution of the most efficient/healthiest leaf regions to whole-plant performance (called Wmax) quantified the spatial efficiency of a photosynthetically heterogeneous plant. Plant survival to water deficit was associated to high S values, as well as with strong and fast recovery of Wmax following soil rewatering. Hence, during stress surviving plants had higher, but more efficient photosynthetic heterogeneity compared to perishing plants. Importantly, S allowed the discrimination between surviving and perishing plants four days earlier than the mean Fv/Fm. A sensitivity analysis from simulated dynamics of Fv/Fm showed that parameters indicative of plant tolerance and/or stress intensity caused identifiable changes in S and Wmax. Finally, an independent comparison of six Arabidopsis accessions grown under well-watered conditions indicated that S and Wmax are related to the genetic variability of growth.

Effects of severe water deficit on plant photosynthetic efficiency. (A) Dynamics of whole-rosette mean Fv/Fm of well-watered (WW) plants and stressed (surviving and perishing) plants under severe water deficit (SWD) as a function of days after four-leaves stage (L4; beginning of SWD) until bolting. Data are means (± SE) of 13–29 plants. (B) 3-D representations of vegetative rosettes under WW and SWD conditions in Fv/Fm false colour (from black pixel values (0) through red, yellow, green, blue to purple (ending at 1)) and their corresponding Fv/Fm distributions during time courses. Asterisks indicate p-value < 0.01 (Hartigan’s dip test) meaning significant departure from unimodality of Fv/Fm values. Arrows indicate rewatering step. (C) Dynamics of the proportion of non-unimodal (i.e., multimodal) plants under WW and SWD after L4 stage until bolting following the Hartigan’s dip test.

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