We have studied the effect of a change in the endogenous hormone equilibria on the competence of tomato (Lycopersicon esculentum) cells to defend themselves against the fungal pathogen Fusarium oxysporum f. sp. lycopersici. Calluses from cvs ‘Davis’ and ‘Red River’, respectively resistant and susceptible to Fusarium and transgenic for an auxin- or cytokinin-synthesizing gene from Agrobacterium tumefaciens, were used. The integration of Agrobacterium hormone-related genes into susceptible cv ‘Red River’ can bring the activation of defense processes to a stable competence as assessed by the inhibition of mycelial growth in dual culture and gem-tube elongation of Fusarium conidia, the determination of callose contents, peroxidase induction and ion leakage in the presence of fusaric acid. This is particularly true when the transformation results in a change of phytohormone equilibria towards an higher cytokin in concentration. On the contrary, in resistant cv ‘Davis’ the inhibition of both fungal growth in dual culture and conidia germination is higher when the hormone balance is modified in favour of the auxins. No significant effect was observed for ion leakage and peroxidase induction, probably because of a constitutive overproduction of cytokinins in ‘Davis’ cells.

Modification of competence for in vitro response to Fusarium oxysporum in tomato cells. II. Effect of the integration of Agrobacterium tumefaciens genes for auxin and cytokinin synthesis.

Broad bean (Vicia faba L. “Inovec”) seeds were artificially aged by means of storage at 30 %, resp. 25 % water content at 25 °C for 7-days to study the consequences on germination, root length and frequency of chromosomal aberrations. Under these conditions, significant changes in all parameters were observed. An increase of frequency of chromosomal aberrations in ana-telophase cells was confirmed by evaluation of c-metaphase cells. Synergic effect of artificial seed ageing was studied on different harvests of old seeds. Possible principles of this effect on cell level are discussed.

Artificial ageing of Vicia faba L. seeds caused by prolongation of G-1 phase

Plant seeds have for a long time been used as a suitable model for the study of aging at the basic cytogenetic level. This chapter is covering 25 years of our experiments with aging focused for an enhancement of DNA repair in plant seeds using a simply method of a ‘storage effect’. The ‘storage effect’ method in plant seeds was developed in past by several authors in series of experiments. This method is based at prolongation of G-1 phase of pre-replication DNA repair from hours to days. It offers a simple and effective enhancement of DNA repair from damage caused by different kinds of xenobiotics. Our idea was to use the same method for old seeds of Vicia faba L. with the synergic effect of their age and mutagen treatment by non-alkylating agent maleic hydrazide or by alkylating agent methyl methanesulphonate, both as S-dependent mutagen with the significant impact to the mutagenicity. The greater the damage is, the better is the possibility to observe significant results in DNA repair. We are reporting here about the examples with a final effect of rejuvenation. Storage of the mutagen treated old seeds in defined conditions for the 8-days appear to be optimal with a significantly lower frequency of chromosome aberrations in root tips of seeds observed. This prolongation of G-1 phase causes a decrease in damage not only from mutagen treatment but also from impact of aging. It resulted in the condition of seeds as if they are younger (from 12 years old to the level of 2 years old). Effect of rejuvenation of old seeds by this combined method was observed for the first time.

G. Vizarova

Papers

The content of free endogenous cytokinins in differently aged seeds of Vicia faba