Involvement of polyamines in the maturation of grapevine (Vitis vinifera L. ‘Mencía’) somatic embryos over a semipermeable membrane

Abstract

The endogenous content of polyamines and the expression of genes involved in their metabolism were analyzed in grapevine (Vitis vinifera L. ‘Mencía’) somatic embryo aggregates to determine the effect of a semipermeable membrane on their maturation in differentiation medium. The endogenous polyamine content in the somatic embryo aggregates was higher in those cultured over the semipermeable membrane and significantly increased with culture time due to an increase in the free polyamine fraction. Free putrescine represented more than 95% of the total free polyamine fraction and significantly peaked in the second week of culture of the somatic embryo aggregates over the semipermeable membrane. This finding appears to be supported by active expression of the VvADC gene and the low free spermidine level. Another significant peak of free putrescine was detected at the end of culture over the membrane, in which free spermidine level remained low despite the VvSPDS2 gene was upregulated. Hence, it is advisable that this increase in free putrescine was supported by back conversion from spermidine through VvPAO expression. As the semipermeable membrane successfully avoided precocious germination of the grapevine somatic embryos, the results support that polyamine metabolism, particularly putrescine metabolism, is involved in their correct maturation.