Investigation of glutathione, salicylic acid and GA3 effects on browning in Pistacia vera shoot tips culture.

摘要

Pistachio (P. vera) is one of the most important horticultural plants growing in Iran. In the light of the economic importance and the edible nuts of pistachio, improvement of in vitro tissue culture for subsequent study on increasing production and quality is necessary. The major limitation facing the in vitro tissue and shoot tip culture of pistachio is browning that results in the death of explants in a few days after cultivation. Browning of tissue is caused by the increasing production of phenolic compounds and their subsequent oxidation by the activity of oxidase enzymes (such as polyphenol oxidase [catechol oxidase]) and their polymerization. Phenylalanine amonia-lyase (PAL) as a branch-point enzyme in phenylpropanoid pathway has a very high effect on development of browning. One of the most important causes of tissues browning in vitro is wounding due to explants excision. Wound induced stress causes an increase in PAL activity with an enhancement of phenylpropanoid production implicated in browning. Therefore, measurement of PAL activity can be used to examine the development of tissue browning. We used the culture of embryos axis on MS medium containing sucrose (30 g/l), agar (7 g/l) and casein hydrolysate (200 mg/l). After 30 days, shoot tips (0.8 cm) were cut and cultured on medium containing compounds mentioned above and 6-benzylaminopurine [benzyladenine] (BAP) at 4.4 micro M (control) with 1, 5 and 10 micro M salicylic acid (SA) or 0.1 and 1 micro M gibberellic acid (GA3) as treatments. Glutathione (GSH) treatment was given by dipping excised ends of the shoot tips into 0.1 mM GSH solution before their culture on MS medium containing BAP. Among all the treatments, GSH reduced the total phenolic compounds best and that it was the most effective in decreasing the PAL and peroxidase activity. This treatment also significantly increased the growth in a better manner, compared to other treatments. It is possible that the fall in PAL activity induced by GSH has limited the production of secondary metabolites in favour of primary metabolism processes supporting the increase in growth..