Photocontrol of somatic embryogenesis and polyamine content in Araujia sericifera petals

Abstract

The effects of photoperiod and end‐of‐day phytochrome control on somatic embryogenesis and polyamine (PA) content in Araujia sericifera petals have been studied. Petals from immature flowers were cultured under 16‐ and 8‐h photoperiods. Far red (FR), red (R) and FR followed by R light treatments were applied at the end of the photoperiods for three weeks. The number of somatic embryos, callus weight and the levels of free and bound PAs in the cultured petal explants were determined 40 days after the beginning of light treatments. Long day (LD) promoted somatic embryogenesis but did not have any significant effect on PA content. Short day (SD) reduced somatic embryogenesis and enhanced total PAs, mainly in the form of bound spermidine. End‐of‐day FR treatment increased PA content and inhibited somatic embryogensis under LD but had no significant effect under SD. This effect of FR on PA levels was cancelled by R and was independent of the presence of silver thiosulphate in the medium. End‐of‐day R treatment reduced the total PA content under SD. However, end‐of‐day R increased or reduced somatic embryogenesis under SD depending on the presence or absence of silver in the medium. The results suggest a photoperiodic control of somatic embryogenesis and PA content in A. sericifera. The effects of end‐of‐day R and FR treatments depend on the length of the photoperiod. This finding and the FR/R photoreversibility of end‐of‐day treatments indicate that phytochrome may be involved in both somatic embryogenesis and accumulation of PA.