NMR Imaging Provides Greater Insight into Seed Germination Processes

“…this imaging study provides insights into the spatial aspects of key events in oilseed rape seeds leading to germination. It demonstrates how seed architecture predetermines the pattern of water intake…”

Seed germination is a fundamental step in establishing a crop. It represents the transition from a dormant seed to a new growing plant. Germination is initiated by the intake of water by the seed in the process of seed imbibition. This water uptake is then followed by the growth of the seeding from the radicle (root) tip.

Seed germination is thus an integral component of agricultural since effective germination is essential for cultivating a good crop. It is therefore not surprising that seed germination has been well studied by scientists in the biotechnological industry. The majority of this research is focused on the factors that impact the timing and rate of germination of a seed, ie, moisture and oxygen availability (exogenous factors) and hormonal, dormancy, and genotype effects (endogenous factors).¹

Nuclear magnetic resonance (NMR) imaging is well accepted as a tool of choice in seed germination research. NMR technology relies on the magnetic moment of the nuclear spin, rather than high-energy radiation, and so is non-invasive and non-damaging. Consequently, NMR imaging technique have provided much valuable information regarding the physical and chemical characteristics of seedlings.⁴

However, the critical process of water uptake, which represents the first step towards seed germination, has been little studied. Further research is needed to evaluate the post-water-uptake events during seed germination and the metabolic processes that are initiated as the seed springs into life and embryo development commences.

It is hoped that furthering our understanding of seed imbibition and the subsequent processes that culminate in seed germination may facilitate the development of new scientific and technological programs for increasing crop yields and potentially eradicating world hunger.^2,3

A recent study by Munz et al used the 500 MHz Bruker AVANCE NMR imaging platform to directly follow the entrance of water into the rapeseed (Brassica napus) seed as well as the pathway it follows to reach the embryo tissues.⁵ Functional NMR was used in combination with computer-aided seed modeling, fluorescence-based respiration mapping, and Fourier transform infrared microscopy to enable analysis of the essential cues that promote seed germination. In addition, the NMR data were used to produce time lapse movies.

The holistic in vivo strategy adopted in this study enabled investigation of the associations between the key processes of seed germination. The nature of water entry and allocation and how these impact subsequent chemical and metabolic events and structural changes were studied.

The investigators discovered an endospermal lipid gap that allows water to be channeled towards the radicle tip. Tissue rehydration was identified as the signal for the commencement of sugar metabolism and lipid utilization. Spatial analysis of the germinating seed revealed that water is imbibed rapidly but unevenly.

The imaging data obtained in this study, provide a more in-depth insight into the changes, both spatial and metabolic, that occur during seed germination. This enhanced understanding will hopefully help researchers refine the processes to optimize seed germination rates, which in turn will maximize crop yields.

References:

1. Bassel GW. To Grow or not to Grow? Trends Plant Sci. 2016;21(6):498-505.
2. Weitbrecht K, Müller K, Leubner-Metzger G. First off the mark: early seed germination. J Exp Bot. 2011;62(10):3289-3309.
3. Née G, Xiang Y, Soppe WJ. The release of dormancy, a wake-up call for seeds to germinate. Curr Opin Plant Biol. 2017;35:8-14.
4. Borisjuk L, Rolletschek H, Neuberger T. Surveying the plant’s world by magnetic resonance imaging. Plant J. 2012;70(1):129-146.
5. Munz E, Rolletschek H, Oeltze-Jafra S, et al. A functional imaging study of germinating oilseed rape seed. New Phytol [published online August 11, 2017]. doi: 10.1111/nph.14736.