The researchers found that agave leaves have an inner core that remains highly hydrated while the outer layer acts as a protective barrier to reduce water loss. [Image: Enrique Castro, CIO]
Agave is one tough desert plant, and in new work, terahertz technology is peeling back the mystery of its extreme drought resistance.
Scientists in Mexico used terahertz spectroscopy and imaging to probe the plant’s ability to retain water through drought conditions (Appl. Opt., doi: 10.1364/AO.547952 ). Not only did the researchers learn about the interior leaf structures that hold water until the plant needs it, but they also found that a key carbohydrate molecule binds itself to water molecules. The terahertz imaging and time-domain spectroscopy allowed the team to track the plant’s water management noninvasively and could lead to better crop management.
The agave plant and its fructans
The researchers, led by Monica Ortiz-Martinez of the Centro de Investigaciones en Optica (CIO), Mexico, investigated a plant called Agave striata—not the agave plant used to make tequila and sweetening syrup, but a close, common relative of it. The succulent contains fructans, which are polymer chains of fructose molecules.
The analysis showed that fructans have a branched chemical structure that forms a kind of porous sponge on which water can be retained. This keeps the plant hydrated despite high temperatures. The illustration shows an Agave striata leaf and the molecular structure of its fructans, with water molecules bound around the fructan chains. [Image: Monica Ortizo-Martinez, CIO]
Traditional methods of studying fructans and similar substances involve gravimetric analysis, which requires cycles of weighing and drying, “making the process destructive and time-consuming,” Ortiz-Martinez and her colleagues wrote.
The team carefully removed individual leaves from greenhouse-grown plants, rinsed them with deionized water and immediately subjected them to imaging with a spectrometer in transmission configuration. To study the hydration dynamics of the fructans, the scientists switched the spectrometer to attenuated total reflection mode and inserted a prism between the aqueous fructan solution samples and the terahertz emitter and receiver. A femtosecond fiber laser with a frequency range of 0.1 to 2 THz powered the spectrometer in both scenarios.
Greater water retention
The imaging revealed two regions inside each leaf: an outer layer of tissue, containing 30 to 40% water by weight, and an inner core made of more than 70% water. The outer layer of the leaf contains chloroplasts for photosynthesis and protects the inner water-storage system.
The absorption spectroscopy of the fructan solution showed that each fructan chain bonds to roughly 320 water molecules—a water-retention capacity two to four times greater than other types of carbohydrates such as maltodextrin.
While this work provides insights into ways to improve agriculture in arid climates, it could also lead to food additives that improve moisture retention and lengthen shelf life of products.