Aquaphotomics Research of Cold Stress in Soybean Cultivars with Different Stress Tolerance Ability: Early Detection of Cold Stress Response

Abstract

The development of non-destructive methods for early detection of cold stress of plants and the identification of cold-tolerant cultivars is highly needed in crop breeding programs. Current methods are either destructive, time-consuming or imprecise. In this study, soybean leaves’ spectra were acquired in the near infrared (NIR) range (588–1025 nm) from five cultivars genetically engineered to have different levels of cold stress tolerance. The spectra were acquired at the optimal growing temperature 27 °C and when the temperature was decreased to 22 °C. In this paper, we report the results of the aquaphotomics analysis performed with the objective of understanding the role of the water molecular system in the early cold stress response of all cultivars. The raw spectra and the results of Principal Component Analysis, Soft Independent Modeling of Class Analogies and aquagrams showed consistent evidence of huge differences in the NIR spectral profiles of all cultivars under normal and mild cold stress conditions. The SIMCA discrimination between the plants before and after stress was achieved with 100% accuracy. The interpretation of spectral patterns before and after cold stress revealed major changes in the water molecular structure of the soybean leaves, altered carbohydrate and oxidative metabolism. Specific water molecular structures in the leaves of soybean cultivars were found to be highly sensitive to the temperature, showing their crucial role in the cold stress response. The results also indicated the existence of differences in the cold stress response of different cultivars, which will be a topic of further research.

Progress and Prospects of the Molecular Basis of Soybean Cold Tolerance

“…Cold stress prevents soybean growth by inhibiting metabolic and physiological activities, such as water uptake, cellular dehydration, and oxidative stresses [ 25 , 26 ]. Aquaphotomics analysis revealed major changes in the water molecular structure in soybean leaves, as well as altered carbohydrate and oxidative metabolism in response to cold stress [ 27 ].…”

Aquaphotomics—Exploring Water Molecular Systems in Nature

“…Out of the 21 published articles, 3 were reviews [ 2 , 3 , 4 ] and 18 were original research papers [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ], that can be roughly separated into 6 categories ( Figure 3 ).…”

“…The majority of the articles, approximately one third, belongs to the field of applications in agriculture and food science [ 8 , 9 , 12 , 13 , 14 , 21 , 22 ], a field from which aquaphotomics originated, and probably the reason why this category is still at the forefront of aquaphotomics development. Following this category are the preprocessing and chemometrics [ 2 , 4 , 15 , 18 ] and fundamental studies [ 5 , 6 , 10 , 17 ].…”

“…Nevertheless, it is very encouraging to notice that the use of short wavelength NIR spectroscopy is gaining popularity. In this Issue, three papers reported the use of short wavelength NIR spectroscopy, in the approximate range of 750–1000 nm, where the 2nd and 3rd overtone of water are located [ 9 , 13 , 21 ]. Furthermore, two research groups presented the results, in parallel, for both the first overtone of water region and higher overtones, demonstrating increased efforts in gaining more clarity in the nature of information that can be gained from each of the regions, and attempts at defining WAMACs similar to the existing ones in the first overtone [ 23 ].…”

“…Only one of the papers in this Special Issue was devoted to plant physiology, using aquaphotomics to explore the cold stress response in five different cultivars of soybean that were engineered to encompass varying levels of tolerance to cold stress [ 9 ]. The study showed that all soybean cultivars have a different water molecular structure in the leaves when the plants are exposed to even mild stress conditions, which is very easy to detect very early.…”