Response of Arabidopsis thaliana and Mizuna Mustard Seeds to Simulated Space Radiation Exposures

Abstract

One of the major concerns for long-term exploration missions beyond the Earth's magnetosphere is consequences from exposures to solar particle event (SPE) protons and galactic cosmic rays (GCR). For long-term crewed Lunar and Mars explorations, the production of fresh food in space will provide both nutritional supplements and psychological benefits to the astronauts. However, the effects of space radiation on plants and plant propagules have not been sufficiently investigated and characterized. In this study, we evaluated the effect of two different compositions of charged particles-simulated GCR, and simulated SPE protons on dry and hydrated seeds of the model plant Arabidopsis thaliana and the crop plant Mizuna mustard [Brassica rapa var. japonica]. Exposures to charged particles, simulated GCRs (up to 80 cGy) or SPEs (up to 200 cGy), were performed either acutely or at a low dose rate using the NASA Space Radiation Laboratory (NSRL) facility at Brookhaven National Lab (BNL). Control and irradiated seeds were planted in a solid phytogel and grown in a controlled environment. Five to seven days after planting, morphological parameters were measured to evaluate radiation-induced damage in the seedlings. After exposure to single types of charged particles, as well as to simulated GCR, the hydrated Arabidopsis seeds showed dose- and quality-dependent responses, with heavier ions causing more severe defects. Seeds exposed to simulated GCR (dry seeds) and SPE (hydrated seeds) had significant, although much less damage than seeds exposed to heavier and higher linear energy transfer (LET) particles. In general, the extent of damage depends on the seed type.

Keywords: Arabidopsis; galactic cosmic rays; mizuna mustard; seeds; solar particle event; space radiation.

Figure 1

Particle tracks simulated within the volume of one cell. (A) A single 300 MeV/n Ti particle track with numerous secondary particles within a cell; (B) 250 MeV/n H particle tracks generated within a cell; (C) simulated GCR1 mixed irradiation field within a cell; and (D) simulated GCR2 irradiation field within a cell.

Figure 2

Effect of 300 MeV/n Ti particles on seed germination, viability, and morphological measurements. (A) Tables of seeds number with percentages of viability, germination, cotyledon deformation, and absence of measurable roots by experimental group. (B) Root length distribution (small circles) in seedlings from control and Ti irradiated seeds. Multiple instances of zero root length are plotted with small jitter so that they can be distinguished. Estimates of 75th percentile root length (orange bars) are shown with 95% confidence limits (dashed lines). (C) Comparative histograms of root-length distributions. (D) Examples of cotyledon deformation. * Indicates p < 0.05 compared to controls.

Figure 3

Effect of 250 MeV/n protons on root length in seedlings grown from control and irradiated Arabidopsis seeds. (A) Arabidopsis seed number and germination rate. (B) Root length distribution (small circles) in seedlings from control and irradiated seeds. Multiple instances of zero root length, including non-germinated seeds are plotted with small random jitter so that they can be distinguished. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). (C) Comparative histograms of root-length distributions in plants from germinated seeds. * Indicates p < 0.05 compared to controls.

Figure 4

Effect of GCRs on root length in seedlings from control and irradiated Arabidopsis seeds. (A) Arabidopsis seed number and germination rate. (B) Root length distribution (small circles) in seedlings from control and Ti irradiated seeds. Multiple instances of zero root length (including non-germinated seeds) are plotted with small random jitter so that they can be distinguished. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). (C) Comparative histograms of root-length distributions in plants from germinated seeds.

Figure 5

The effect of GCR-2 scenario on root length reduction in seedlings developed from control and irradiated dry seeds. (A) Arabidopsis seed number and germination rate. (B) Root length distribution (small circles) in Arabidopsis seedlings from control and irradiated seeds. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). Multiple instances of zero root length (including non-germinated seeds) are plotted with small jitter so that they can be distinguished. (C) Mizuna seed number and germination rate. (D) Cotyledon deformation rate in Mizuna seedlings. (E) Root length distribution (small circles) in mizuna seedlings from control and irradiated seeds. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). Multiple instances of zero root length (including non-germinated seeds) are plotted with small jitter so that they can be distinguished. * Shows p < 0.05 compared to controls.

Figure 6

The effect of SPE scenarios on root length reduction in seedlings developed from control and irradiated imbibed seeds. (A) Arabidopsis seed number and germination rate. (B) Root length distribution (small circles) in Arabidopsis seedlings from control and irradiated seeds. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). Multiple instances of zero root length (including non-germinated seeds) are plotted with small jitter so that they can be distinguished. (C) Mizuna seed number and germination rate. (D) Cotyledon deformation rate in Mizuna seedlings. (E) Root length distribution (small circles) in mizuna seedlings from control and irradiated seeds. Multiple instances of zero root length (including non-germinated seeds) are plotted with small jitter so that they can be distinguished. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). * Indicates p < 0.05 compared to controls.

Figure 6

The effect of SPE scenarios on root length reduction in seedlings developed from control and irradiated imbibed seeds. (A) Arabidopsis seed number and germination rate. (B) Root length distribution (small circles) in Arabidopsis seedlings from control and irradiated seeds. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). Multiple instances of zero root length (including non-germinated seeds) are plotted with small jitter so that they can be distinguished. (C) Mizuna seed number and germination rate. (D) Cotyledon deformation rate in Mizuna seedlings. (E) Root length distribution (small circles) in mizuna seedlings from control and irradiated seeds. Multiple instances of zero root length (including non-germinated seeds) are plotted with small jitter so that they can be distinguished. Estimates of median root length (orange bars) are shown with 95% confidence limits (dashed lines). * Indicates p < 0.05 compared to controls.

Figure 7

A plot of estimated ratios (treatment to control) of median root length (proton and CGR) or 75th percentiles (Ti) along with 95% confidence intervals showing that the Arabidopsis seedlings from irradiated seeds generally have shortened root length. Larger uncertainties for Ti exposure reflect the smaller sample size as well as the failure of many seeds to germinate or produce measurable roots. * Indicates p < 0.05 compared to controls.