Abstract
Heavy rainfall causes flooding of natural ecosystems as well as farmland, negatively affecting plant performance. While the responses of the wild model organism Arabidopsis thaliana to such stress conditions is well understood, little is known about the responses of its relative, the important oil crop plant Brassica napus. For the first time, we analyzed the molecular response of Brassica napus seedlings to full submergence in a natural light-dark cycle. We used two cultivars in this study, a European hybrid cultivar and an Asian flood-tolerant cultivar. Despite their genomic differences, those genotypes showed no major differences in their responses to submergence. The molecular responses to submergence included the induction of defense- and hormone-related pathways and the repression of biosynthetic processes. Furthermore, RNAseq revealed a strong carbohydrate-starvation response under submergence in daylight, which corresponded with a fast depletion of sugars. Consequently, both B. napus cultivars exhibited a strong growth repression under water, but there was no indication of a low-oxygen response. The ability of the European hybrid cultivar to form a short-lived leaf gas film neither increased underwater net photosynthesis, underwater dark respiration nor growth during submergence. Due to the high sensitivity of both cultivars, the analysis of other cultivars or related species with higher submergence tolerance is required in order to improve flood tolerance of this crop species. One major target could be the improvement of underwater photosynthesis efficiency in order to enhance submergence survival.
Highlights
During their lifetime, plants are exposed to many different environmental conditions
The O2 microsensor was connected to a pico ampere meter, and was calibrated prior to each series of experiments in air-purged water (267.8 μmol O2 l−1 equivalent to 20.6 kPa pO2 at 23C) and in an oxygen-free solution (2 g ascorbate in 100 ml 0.1 M NaOH); the signal from the O2 microsensor was logged on a computer every 1 s (Logger, Sensortrace 3.2, Unisense A/S)
AT4G27450 as well as the PHLOEM PROTEIN 2-A13 (Figure S4). This finding and the fact that neither the genes for fermentative enzymes alcohol dehydrogenase (ADH) nor PYRUVATE DECARBOXYLASE (PDC) were up-regulated in our experiments suggests that there was no severe hypoxia during submergence
Summary
Plants are exposed to many different environmental conditions. Two types of survival strategies have been observed to tolerate flooding (summarized in van Veen et al, 2014; Voesenek & BaileySerres, 2015): (1) Several plant species avoid oxygen deficiency by multiple mechanisms that favor gas transport, such as development of adventitious roots, formation of aerenchyma in roots and leaves, gas films on leaves as well as elongational growth to restore contact to oxygen-rich air (summarized in Voesenek & Bailey-Serres, 2015; Mustroph et al, 2018; Yamauchi et al, 2018). We detected cultivar-specific difference in the ability to form gas films, but this did not cause differences in the response to submergence or the survival under stress
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