Effects of nitrogen in growth and fructan metabolism in Vernonia herbacea (Vell.) Rusby

Author(s)

Patricia Gaya de Carvalho

• Document type: Master's Dissertation
• Press: Piracicaba. , ilustrações.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2005-09-05

Examining board members

Maria Angela Machado de Carvalho; Marília Gaspar; Nair Massumi Itaya

• Advisor: Maria Angela Machado de Carvalho
• Field of knowledge: Biological Sciences - Botany
• Indexed in: Banco de Dados Bibliográficos da USP-DEDALUS; Biblioteca Digital de Teses e Dissertações - USP
• Location: Universidade de São Paulo. Biblioteca Central da Escola Superior de Agricultura Luiz de Queiroz; ESALQ-BC/t581.19248 85973; C331e

Abstract

Nitrogen is the most limiting element to plant development. Vernonia herbacea (Vell.) Rusby, Asteracea from the cerrado, bears underground organs (rhizophores) which accumulate inulin-type fructans. Previous studies showed that nutrient solution containing 1.3 mmol L-1 NO3 - (N-Limited treatment) promoted fructan accumulation in rhizophores and decrease of aerial biomass, while the opposite occurred in plants treated with nutrient solution containing 10.7 mmol L-1 NO3 - (N-sufficient treatment). However, as the activities of fructan metabolizing enzymes were not measured in these plants, new experiments were designed with this purpose. Thus, considering the importance of studies on mineral nutrition for the adjustment of the fertilization treatment, aiming at high contents of fructan and increase in plant productivity, the aim of this project was to analyse the effect of nitrogen on growth and biomass allocation, on fructan content and composition, on the activity of enzymes involved in fructan metabolism (SST, FFT, FEH and INV) in rhizophores, as well as on the activity of nitrate reductase (NR) and nitrogen content in leaves and rhizophores of V. herbacea. In the present work, plants treated with a low nitrogen concentration (2.5 mmol L-1 NO3 -) presented higher fructan biossynthetic activities than those treated with higher nitrogen concentration (11.9 mmol L-1 NO3 -). Oppositely, a higher mobilization activity occurred under high nitrogen concentration. Fructan content was higher in plants under low nitrogen concentration, in accordance with the higher biosynthetic activity in this treatment. However, higher aerial and underground biomass were detected in the 2.5 mmol L-1 NO3 - plants, indicating that growth was not limited under low levels of nitrate. Therefore, in order to improve the understanding of the effect of nitrate on growth, biomass allocation and fructan metabolism in V. herbacea, a new experiment was performed in which different concentrations of nitrate concentration (0, 2.5, 5.0, 10.0, 15.0 mM) were supplied in the same conditions mentioned above. The results showed that 10 mM nitrate was the most efficient concentration for total plant biomass and fructan accumulation in the rhizophore. It was also shown that, besides fructan, nitrate is accumulated in the rhizophores, but is preferably assimilated in leaves, where RN activity is higher. Considering results obtained with 10 mM nitrate, a third experiment was done in order to compare the effect of different nitrogen sources on growth of V. herbacea. The plants were treated with nutrient solutions containing ammoniun ((NH4)2SO4), nitrate(KNO3) and a mixture of nitrate and ammoniun (NH4NO3), both at a final concentration of 10 mM. No preference for the nitrogen source was observed when growth parameters were analysed. Therefore, the results suggest that plants of V. herbacea can be cultivated under any of the nitrogen sources used in this study. (AU)

• FAPESP's process: 02/11226-5 - Effect of the availability of nitrate in the content of fructans and in the enzymes of their metabolism in Vernonia herbacea (Vell.) Rusby
• Grantee: Patrícia Gaya de Carvalho
• Support Opportunities: Scholarships in Brazil - Master