Adventitious shoot formation in cultured leaf explants of quince and pear is accompanied by different patterns of ethylene and polyamine production, and responses to aminoethoxyvinylglycine.

The gaseous environment inside culture vessels is an important factor affecting growth and differentiation of plant cell and tissue culture. Carbon dioxide (CO2) and ethylene (C2H4), in particular, play important roles. The effect of reduced gas exchange in sealed petri dishes has previously been shown to strongly inhibit adventitious shoot formation in cultured leaf explants of quince ‘BA29’, but has not been investigated in pear. In the present work, the accumulation of CO2 and C2H4 in petri dishes was quantified during the shoot induction and development phases in quince (Cydonia oblonga Mill.) ‘BA29’ and pear (Pyrus communis L.) ‘Conference’ that have a higher and lower regeneration capacity, respectively, on medium supplemented with 4.5 M thidiazuron (TDZ) and 5.4 M -naphthaleneacetic acid (NAA). In order to evaluate the specific role of C2H4 on the shoot-forming process, the effect of treatment with the inhibitor of C2H4 biosynthesis aminoethoxyvinylglycine (AVG) was also evaluated during the shoot induction phase. The results showed that AVG strongly reduced both C2H4 accumulation and the production rate of C2H4, without affecting CO2 accumulation, in both species, whereas it differentially affected regeneration capacity, enhancing it in quince and reducing it in pear. A time-course analysis of free and soluble conjugated polyamine (PA) titres was also performed in control vs. AVG-treated quince and pear explants during the induction phase. Quince explants exhibited a marked peak in free and conjugated spermidine on day-7 in culture, while pear explants did not. AVG did not alter PA levels or the PA profile in either species. The addition of AVG to the induction medium is recommended to improve shoot regeneration in quince 'BA 29' leaf explants in culture systems that prevent optimal gas exchanges. Instead, the genotype-specific low regeneration capacity of pear prevailed over the effect of AVG treatments in our experimental conditions.