Sazonalidade no acúmulo de frutanos em órgãos subterrâneos de gomphrena marginata seub. (AMARANTHACEAE) em área de campo rupestre

Abstract

The climatic seasonality is one of the main features of Cerrado and as a consequence, the vegetation of this biome has developed several adaptations. Gomphrena marginata Seub. is a herbaceous of ‘campos rupestres’ that has thick underground structure and occurs in a region marked by climatic seasonality. In this context, this study aims to evaluate the occurrence and the seasonality of accumulation of carbohydrates like fructans in underground organs of G. marginata and their relationship with soil water availability and hydric relations of plants. Sample of G. marginata were collected monthly from August 2010 to July 2011 in the ‘campos rupestres’ of Environmental Preservation Area "Complexo Paisagístico Serra Resplandecente " in the city of Itacambira-Minas Gerais State (16°59'47"S, 43°20 '01"W). To this end, monthly quantitative analysis of the levels of total fructose, fructo-polysaccharides, fructo-oligosaccharides, reducing sugars and free proline were carried out in underground organs of G. marginata. It was made qualitative analysis of carbohydrates by Thin Layer Chromatography (TLC) and High Performance Anion Exchange Chromatography with Pulsed Amperometric Detection (HPAEC/PAD). Regarding the hydric aspects, it was established soil humidity, the relative content of water (TCW) and osmotic potential from underground organs cell sap. In addition, rainfall data (mm), relative humidity (RH) and average air temperature were obtained from the website of the Institute of Agricultural Sciences of UFMG. Data were analyzed using simple correlation (Pearson) and all the environmental parameters of hydric and biochemical relations. It was used the "t" Student test for assessing the significance of the correlations in 5% level of probability. During the rainy season (September 2010 to March 2011) it was observed an increase of reducing sugars content while there was a decrease in the content of fructo-polysaccharides. Such changes were also detected in the analysis by TLC and HPAEC / PAD. From August to December it was observed high amount of free fructose and sucrose indicating the occurrence of depolymerization of the fructo-polysaccharides chain. In field it was observed that the flowering period of this species occurred predominantly from September to November 2010. Probably reserve carbohydrates (fructo-polysaccharides) were depolymerized and translocated to the shoot of the plant which was in intense development. During the dry period it was found correlations between the reducing sugar content, parameters RH and soil humidity. In this period there was an intense accumulation of fructo-polysaccharides. This accumulation can be associated with translocation of photoassimilates to the underground system before leaf senescence and abscission which was observed especially in the months of June and July 2010. The species G. marginata probably has strategies to avoid loss of water as the control of stomatal movement and / or acceleration of leaf senescence and abscission. The proline content showed significant positive correlations with the TCW. However, due to the low concentration observed its performance in the osmoregulation is questionable, although it is not ruled out the possibility of being a flag. It was concluded that the accumulation of fructans in the underground organs in G.marginata is seasonal. The depolymerization of fructo-polysaccharides occurs during the rainy season which coincides with the period of plants flowering. On the other hand, during the dry period occurs and accumulation of long chain fructans