Caracterização fisiológica e nutritiva da clorose férrica em citrinos

Tese dout., Ciências Agrárias, Produção Vegetal, Unidade de Ciências e Tecnologias Agrárias, Universidade do Algarve, 2000

Root ferric chelate reductase is regulated by iron and copper in straberry plants

In the present experiment, we studied the interaction between copper (Cu) and iron (Fe) in strawberry plants grown in nutrient solutions containing different concentrations of Fe. Plants grown in the absence of iron (Fe0) had the characteristic symptoms of Fe deficiency, with smaller chlorotic leaves, less biomass, acidification of the nutrient solution, and roots that were smaller and less ramified, while no symptoms of Fe deficiency were observed in plants grown with Fe. A greater amount of Cu was found in roots of chlorotic plants than in those grown with Fe, while plants grown with 20M of Fe (Fe20) in the nutrient solution had a greater amount of Fe compared with plants from the other treatments. Chlorotic plants (Fe0) and plants grown with the greatest level of Fe (Fe20) had a greater root ferric chelate reductase (FC-R; EC 1.16.1.17) activity compared with the other treatments with 5 or 10M Fe in the nutrient solution. The same pattern was obtained for relative FC-R mRNA concentration and for the sum of Fe and Cu contents in shoots (leaves plus crowns). The DNA obtained from amplification of the FC-R mRNA was cloned and several of the inserts analysed by single strand confirmation polymorphism (SSCP). Although there were different SSCP patterns in the Fe20 treatment, all the inserts that were sequenced were very similar, excluding the hypothesis of more than one FC-R mRNA species being present. The results suggest that Cu as well as Fe is involved in FC-R expression and activity, although the mechanism involved in this regulation is unknown so far. Both small contents of Fe and Cu in plants led to an over-expression of the FC-R gene and enhanced FC-R activity in strawberry roots.

Tolerance of young (Ceratonia siliqua L.) carob rootstock to NaCl

One-year-old carob (Ceratonia siliqua L.) rootstock was grown in fertilised substrate to evaluate the effects of NaCl salinity stress. The experiment consisted of seven treatments with different concentrations of NaCl in the irrigation water: 0 (control), 15, 30, 40, 80, 120 and 240 (mmol L(-1)), equivalent to electrical conductivities of 0.0, 1.5, 2.9, 3.9, 7.5, 10.9 and 20.6 dS m(-1), respectively. Several growth parameters were measured throughout the experimental period. At the end of the experiment, pH, extractable P and K, and the electrical conductivity of the substrate were assessed in each salinity level. On the same date, the mineral composition of the leaves was compared. The carob rootstock tolerated 13.4 dS m(-1) for a period of 30 days but after 60 days the limit of tolerance was only 6.8 dS m(-1). Salt tolerance indexes were 12.8 and 4.5 for 30 and 60 days, respectively. This tolerance to salinity resulted from the ability to function with concentrations of Cl(-) and Na(+) in leaves up to 24.0 and 8.5 g kg(-1), respectively. Biomass allocation to shoots and roots was similar in all treatments, but after 40 days the number of leaves was reduced, particularly at the larger concentrations (120 and 240 mmol NaCl L(-1)). Leaves of plants irrigated with 240 mmol NaCl L(-1) became chlorotic after 30 days exposure. However, concentrations of N, P. Mg and Zn in leaves were not affected significantly (P > 0.05) by salinity. Apparently, K(+) and Ca(2+) were the key nutrients affected in the response of carob rootstocks to salinity. Plants grown with 80 and 120 mmol L(-1) of NaCl contained the greatest K. concentration. Na(+)/K(+) increased with salinity, due to an elevated Na(+) content but K(+) uptake was also enhanced, which alleviated some Na. stress. Ca(2+) concentration in leaves was not reduced under salinity. Salinization of irrigation water and subsequent impacts on agricultural soils are now common problems in the Mediterranean region. Under such conditions, carob seems to be a salt as well as a drought tolerant species. (C) 2010 Elsevier B.V. All rights reserved.