DOI: 10.5061/dryad.2fqz612w1
title: Morphological and transcriptomic responses/acclimations of erect-type submerged macrophyte Hydrilla verticillata both at low-light exposure and light recovery phases

description: Light intensity is a determinant for submerged macrophytes. Little is
 known about their molecular responses to low-light exposure, despite being
 more informative and responsive than morphological traits. For erect-type
 submerged macrophytes, the stem is more crucial relative to the leaf in
 acclimation to low-light stress, but receives less attention. We
 determined morphological and stem transcriptomic responses/acclimations of
 Hydrilla verticillata to extremely and mildly low light (7.2 and 36 μmol
 photons m–2 s–1, respectively), i.e. EL and ML, with the radiation
 intensity of 180 μmol photons m–2 s–1 as the control. Low-light exposure
 continued for nine days, followed by a seven-day recovery phase (180 μmol
 photons m–2 s–1). At the exposure phase, the low-light treatments, in
 particular the EL, decreased relative growth ratio, but induced greater
 height and longer stem internode distance and epidermal cell. Such
 responses/acclimations continued into the recovery phase, despite more or
 less changes in the magnitude. Transcriptome showed that the
 photosynthetic system was inhibited at the exposure phase, but the
 macrophyte adjusted hormone synthesis relating to cell division and
 elongation. Moreover, the EL activated cell stress responses such as DNA
 repair. Following light recovery, the macrophyte exhibited strong-light
 response, although energy metabolism enhanced. Especially, the EL-enriched
 pathways relating to anthocyanin synthesis at such phase, indicating an
 activation of photoprotective mechanism. Our findings suggest that
 negative influences of low light occur at both low-light exposure and
 recovery phases, but submerged macrophytes would acclimate to light
 environments. Transcriptome can show the molecular basis of plant
 responses/acclimations, including but not limited to morphology. This
 study establishes a bridge connecting morphological and molecular
 responses/acclimations.
description: At the end of both low-light exposure and light
 recovery phases, we chose three replicated plastic bottles from each
 growth chamber and determined morphological parameters of <em>H.
 verticillata</em>. Two healthy individuals from each plastic bottle
 were harvested, washed, and dried with filter paper to determine the total
 biomass, the number of stem internodes, and the average distance of stem
 internodes. In addition, plant height and stem diameter (at 5 cm down the
 tip) were measured with a ruler (0.1 cm precision) and a micrometer (0.02
 mm precision), respectively. After the measurement, the <em>H.
 verticillata</em> individuals in each plastic bottle were separated
 into leaves, stems and roots, oven-dried at 80°C to a constant weight, and
 then weighed to obtain the dry weight. The stem mass ratio was defined as
 the ratio of stem dry weight to total dry weight. Relative growth rate
 (RGR) was calculated as:                      
                                                                          
                    
 RGR=<em>W</em><sub>1</sub>-<em>W<sub>2</sub></em>/∆T where <em>W</em><sub>1</sub> is the initial fresh weight (mg), <em>W</em><sub>2</sub> is the final fresh weight (mg), and ∆<em>T</em> is the time (d). In addition, a scan with the electron microscope (JSM-5610LV, Thermo Fisher Scientific, USA) was used to determine stem epidermal cell length (at least 15 cells per sample) at 5 cm down the tip.
description: # Morphological and transcriptomic responses/acclimations of erect-type
 submerged macrophyte Hydrilla verticillata both at low-light exposure and
 light recovery phases
 [https://doi.org/10.5061/dryad.2fqz612w1](https://doi.org/10.5061/dryad.2fqz612w1) ## Description of the data and file structure **Data collection** At the end of both low-light exposure and light recovery phases, we chose three replicated plastic bottles from each growth chamber, and determined morphological parameters of *H. verticillata*. Two healthy individuals from each plastic bottle were harvested, washed, and dried with filter paper to determine the total biomass, the number of stem internode, and the average distance of stem internode. In addition, plant height and stem diameter (at 5 cm down the tip) were measure with a ruler (0.1 cm precision) and a micrometer (0.02 mm precision), respectively. After the measurement, the *H. verticillata* individuals in each plastic bottles were separated into leaves, stems and roots, oven dried at 80 <sup>o</sup>C to a constant weight, and then weighed to obtain the dry weight. The stem mass ratio was defined as the ratio of stem dry weight to total dry weight. Relative growth rate (RGR) was calculated as RGR=*W*<sub>2</sub>-*W*<sub>1</sub>/∆*T* where *W*<sub>1</sub> is the initial fresh weight (mg), *W*<sub>2</sub> is the final fresh weight (mg), and ∆*T* is the time (d). In addition, a scan with the electron microscope (JSM-5610LV,Thermo Fisher Scientific, USA) were used to determine stem epidermal cell length (at least 15 cells per sample) at 5 cm down the tip. **Data description** Light irradiance intensity generally exerted significant effects on morphological traits, and the effects on plant height and stem internode number did not vary significantly between the low-light exposure and the recovery phases. At the end of low-light exposure phase, the decreased light irradiance, especially the EL treatment, induced significant increases in plant height, stem internode distance, stem mass ratio, as well as significant decreases in internode number, fresh weight, stem diameter, and RGR. Moreover, the length of stem epidermal cell obviously increased with the decrease of light intensity. It is worth noting that such influences from low light continued into the light recovery phase, although the magnitudes had more or less changes. **Transcriptome data** Transcriptomics data used in this study are publicly available from NCBI (BioProject ID PRJNA977960). ##