Abstract
The high fructan contents in underground organs of Cerrado species, high water solubility, and fast metabolism of these compounds highlight their role as carbon storage and as an adaptive feature in plants under drought. In this study, we showed that anatomical structure, in association with soluble compounds and metabolism of inulin-type fructans were modified in rhizophores of Crysolaena obovata submitted to water suppression and recovery after re-watering. Plants were subjected to daily watering (control), suppression of watering for 22 days (water suppression) and suppression of watering followed by re-watering after 10 days (re-watered). Plants were collected at time 0 and after 3, 7, 10, 12, 17, and 22 days of treatment. In addition to changes in fructan metabolism, high proline content was detected in drought stressed plants, contributing to osmoregulation and recovery after water status reestablishment. Under water suppression, total inulin was reduced from approx. 60 to 40%, mainly due to exohydrolase activity. Concurrently, the activity of fructosyltransferases promoted the production of short chain inulin, which could contribute to the increase in osmotic potential. After re-watering, most parameters analyzed were similar to those of control plants, indicating the resumption of regular metabolism, after water absorption. Inulin sphero-crystals accumulated in parenchymatic cells of the cortex, vascular tissues and pith were reduced under drought and accompanied anatomical changes, starting from day 10. At 22 days of drought, the cortical and vascular tissues were collapsed, and inulin sphero-crystals and inulin content were reduced. The localization of inulin sphero-crystals in vascular tissues of C. obovata, as well as the decrease of total inulin and the increase in oligo:polysaccharide ratio in water stressed plants is consistent with the role of fructans in protecting plants against drought.
Highlights
Water is the most important and abundant natural resource, and the most limiting environmental factor during the annual growth cycle of plants
The rhizophores presented a turgid aspect in RW plants at days 12, 17, and 22 (Figures 2D,E,F), which paralleled the recovery of water content and water potential of these organs after re-watering
Water suppression allowed a gradual development of water deficit in soil and in plants of C. obovata, as previously reported (Garcia et al, 2011), leading to pronounced structural and metabolic changes, including fructans and proline
Summary
Water is the most important and abundant natural resource, and the most limiting environmental factor during the annual growth cycle of plants. As the reduction in water availability progresses, tolerant plants gradually adjust their metabolism to cope with this condition (Chaves et al, 2002, 2003). Water stress affects many physiological and biochemical processes, resulting in metabolic changes that involve carbohydrates and other compatible solutes that are known to contribute to osmotic adjustment (Bajii et al, 2001). Among them are the inorganic ions, amino acids, such as proline and glutamate, sucrose and its soluble derivatives, including fructans. As widely shown, these compounds contribute to keep the water status of the cell, preventing dehydration and cell damage caused by formation of reactive oxygen species (Hoekstra et al, 2001; Peshev et al, 2013). Consensus on the integral roles of proline accumulation on stress adaptation remains still controversial (Verbruggen and Hermans, 2007; Kavi Kishor and Sreenivasulu, 2013), and evidences suggest that it plays more than one function serving as osmoticum, source of carbon and nitrogen and regulatory signal at the same time (Hare and Cress, 1997)
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