Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

ARABIDOPSIS THALIANA MUTANTS RESISTANT TO CAESIUM OBTAINED BY “T-DNA TAGGING”: ISOLATION, CHARACTERIZATION AND ANALYSIS WITH ADVANCED PHYSICAL TECHNIQUES

MARMIROLI M.*, VISIOLI G.*, ANTONIOLI G.**, MAESTRI E.*

* Dip. Scienze Ambientali, Università degli Studi di Parma

Tel. 0521 905687; Fax 0521 905665

maestri@unipr.it

** Dip. di Fisica, Università degli Studi di Parma

Arabidopsis thaliana, caesium, T-DNA tagging, microfluorescence, microanalysis

Arabidopsis thaliana lines, ecotype Wassilewskija, containing T-DNA (T-DNA insertion lines obtained by the Nottingham Arabidopsis Stock Center) have been utilized for an extensive study on tolerance to Caesium ions, in the natural stable form, in synthetic media added with different Potassium concentrations. It has in fact been demonstrated that sensitivity to Cs depends on K concentration (Sheahanan et al., 1993 Plant J. 3:647). Plants which were able to grow in the presence of Cs doses inhibiting the growth of wild type plants (600 mM) have been selected by screening at least 1200 seeds from each of 49 pools of 100 T-DNA insertion lines. Confirmation of the resistant phenotypes has been obtained by repeating the selection process in the same conditions. Surviving plants have been analyzed by means of PCR-amplification of genomic DNA to confirm the presence of T-DNA fragments. In this way, 10 Cs-resistant lines have been confirmed. Two of these plants, “a063c” and “a171f”, have been brought to flowering and seed setting in order to perform the genetic and molecular analysis in the following generations. In order to characterize the physiological mechanism of Cs resistance in these mutants, two technologies have been applied for measuring Cs intake: synchrotron-radiation-induced X-ray microfluorescence (m-SRXF), carried out at the LURE laboratories (France), and SEM/EDX microanalysis, carried out at the University of Parma. The data obtained by comparing sensitive and resistant plants through m-SRXF are summarized in Table I (cps = counts per second of X-ray photons emitted by the sample).

	w.t.	a171f	a063c
K	55000 cps	7000 cps	9000 cps
Ca	20000 cps	4500 cps	6000 cps
Cs	12000 cps	500 cps	450 cps
K/Cs	4.5	14	20
K/Ca	2.75	1.6	1.5
Ca/Cs	1.6	9.0	13.3

It can be argued from the data that the resistance to Cs in the mutants is associated to a 90% reduction in the intake of ions from the medium. At the same time, also K intake is reduced by 80%. The K/Cs ratio in resistant mutants is higher than in wild type plants. Similarly, a reduction in Ca intake can be evidenced, without however a corresponding modification of the K/Ca ratio in sensitive and resistant plants. Therefore, in resistant plants the mutation leads to a reduction in intake for different ions (K, Ca, Cs) with more pronounced effects on Cs intake. This effect could be attributed to the existence of specific ion channels for Cs, which could however be utilized less efficiently and not exclusively also for Ca and K intake. Genetic analysis is currently in progress by exploiting T-DNA tagging of the two mutants.