Nutrição mineral no crescimento e no metabolismo de carboidratos soluveis em Vernonia herbacea (Vell.) Rusby

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Vernonia herbacea is a herbaceous, perem1ial Asteraceae, native to the Brazilian cerrado. The plants have underground organs, known as rhizophores, which accumulate :fructans of the inulin type. Fructose polymers have been associated to stress conditions, such as water and nutritional defficiency and low temperatures acting as osmotic regulators for the plant. Fructans have an outstanding economic importance due to their application in the food and pharmaceutical industries. These compounds have been successfully used in the prevention of intestinal diseases promoting the growth of bificobacteria. In addition, :fructans are not absorbed by the human organism, which makes these compounds useful in the production of alternative low calorie sugar. Among all the external factors yet reported to stimulate the biosynthesis of :fructan, handling of nutrient application showed to be a very common practice. The aim of the present study was to investigate the effect of nutrient supply, with emphasis on nitrogen, in the: fructan contents of V. herbacea plants. As a secondary objective, we aimed to understand how carbohydrate metabolism interacts with plant growth in V. herbacea. Previous results have shown that growth of rhizophores can be limited when Hoagland solution is added to plants of V. herbacea. Thus a nutrient solution (named Vernonia solution) was formulated based on the chemical constituents of V. herbacea leaves. When compared to Hoagland solution, Vemonia solution with 50% ionic strength had a positive effect on growth after 180 days of cultivation, increasing the production of rhizophores and :fructans per plant. On the other hand an increase in the growth of aerial organs was observed when complete Hoagland or Vernonia solution (100% ionic strength) was added to the plants. To investigate how plants behave under nutritional stress conditions, plants previously cultivated in N-NO3- enriched Vernonia solution (10.7 mmol/L) were transferred to N-NO3 defficient Vemonia solution (1.3 mmol/L). Physiological and metabolical changes were detected in plants in response to nutritional stress. An increase in the biomass of the aerial organs was observed 30 days after the beginning of the treatments. Between 90 and 180 days, when fructan accumulation occurred more intensively, fructan concentration in plants submitted to nitrogen deficiency was higher, although fructan production per plant was superior in plants grown in the nitrogen-enriched solution. Total soluble leaf protein decreased slowly dose to the senescence phase and this decrease was more intense in plants under nutritional stress. These results suggest the occurrence of mobilization of organic nitrogen towards the rhizophores, reflected by the increase in protein and fructans. Photosynthesis was reduced at day 30 in plants cultivated in both nitrate solutions and this reduction could be related to an increase of leaf carbohydrate concentration. This fact points to the hypothesis that photosynthesis is regulated by soluble carbohydrate content. To provide basic information for the sustainable use of the cerrado vegetation, plants of V. herbacea were cultivated in a cerrado area and received different concentrations of nitrogen solution as (NIL)2S04. After 12 months, growth was stimulated only in plants receiving 6 to 12 kg/ha of nitrogen. Plants treated with 24 kg/ha of nitrogen accumulated 6.0 g fructan per plant, while in control plants, not treated with supplementary N, this value was only 3.5 g. These results indicate that 24 kg/ha of nitrogen is the concentration recommended for fructan production by plants of V. herbacea in cerrado soils

ASSUNTO(S)

ecofisiologia frutanos vernonia

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