Ethylene and ABA crosscommunication and plant growth response to salt stress in tomato Solanum lycopersicum L

Picarella, M.E.1, Antonelli, M.G.1, Astolfi, S.1, Zuchi, S.1, Vernieri, P.2 and Soressi, G.P.1

1Dipartimento di Agrobiologia e Agrochimica, Sezione Genetica, Universita della Tuscia, Via C. De Lellis, I-01100 Viterbo, Italy. 2Dipartimento di Biologia delle Piante agrarie, Universita di Pisa, V.le delle Piagge, 23-56124 Pisa. (*Corresponding author: [email protected])

Ethylene (ET) is a signal molecule involved in the regulation of gene expression during adaptation to abiotic stresses. The relationship between ET and ABA production in vegetative tissues under abiotic stresses appears mostly controversial. In order to ascertain the interplay between ET and ABA in young plants (5th leaf stage), grown hydroponically in control (3 mS cm-1) and salt stress (10 mS cm-1) conditions, ET emission, ABA content and dry weight (DW) of roots, basal and apical leaves were measured in five different tomato genotypes: cv Edkawi (EDK), salt tolerant; cv Gimar (GIM), relatively salt sensitive and its near isogenic line for the nor gene (NOR) defective in ET synthesis; the ABA mutants sitiens (SIT) and notabilis (NOT), both with different ABA biosynthetic capacity (8% vs 47%).

The recorded data (Fig. 1) showed that, under salt stress, ET production was either depressed or significantly unaffected in all the genotypes with the exception of SIT where meanly a fivefold increase of this hormone was evidenced in basal and apical leaves. ABA concentration in roots was significantly higher in EDK, GIM, SIT and in apical leaves of NOR and NOT. Interestingly the ABA mutants displayed ABA values comparable to those of the other genotypes. The salt treatment affected root and leaf DW (data not shown) of GIM, NOT, SIT and NOR (excluding apical leaf), but not of EDK.

In leaves of EDK and GIM, the salt induced an ET decrease not correlated with the ABA concentrations which remain in a steady state, while a negative correlation is evident in their root system. In the two ABA-deficient mutants, a clear general view of an interaction between

ABA and salt stress cannot be addressed except for root of SIT similarly to that of EDK and GIM. Despite the extremely reduced ET emission in the nor mutant, a negative interaction with ABA is given for apical leaf. According to our experimental data a negative counteract between the two hormones cannot be ruled out. Under salt stress, the physiological pathways of the two hormones and consequently their interaction are likely influenced by the plant genetic background and/or the growth conditions.

The unexpected ABA accumulation in NOT and SIT could be explained by alternative pathways acting behind the mutation steps. This fact together with our data on ABA concentrations unaffected by salt stress, suggest the existance of a complex process regulating ABA homeostasis.

According to the DW data, the salt treatment induced growth inhibition of GIM, NOR (except for apical leaf), NOT and SIT; only EDK, cos-titutively salt tolerant, was unaffected. The hypothesis that the ET high level of SIT in both control and stress conditions be responsible of its reduced growth does not fit the other genotypes.

Possibly other mechanisms independent of ET and ABA in the salt/ osmotic stress adaptation process are responsible for the growth reduction of plants.

10 J

Sir GM NOR NOT S[T

Fig. 1. Ethylene release and ABA content in five tomato genotypes. (Grey colour 3 mS cm-1; black colour 10 mS cm-1; solid case: root; squared case: basal leaf; barred case: apical leaf).

10 J

Sir GM NOR NOT S[T

Fig. 1. Ethylene release and ABA content in five tomato genotypes. (Grey colour 3 mS cm-1; black colour 10 mS cm-1; solid case: root; squared case: basal leaf; barred case: apical leaf).

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