Effect of disturbed photoperiod on the surface structures of ripening Scots pine (Pinus sylvestris L.) seeds

Abstract

The role of disturbed photoperiod on the developing surface layers of ripening Scots pine (Pinus sylvestris L.) seeds was studied from August 14 to October 30. The embryo sizes of both the light-treated and the control seeds were examined by the X-ray method prior to germination tests. The anatomical details of resin-embedded seeds were examined by fluorescence and light microscopy. The timing of the ripening process of the surface structures was described and documented. The greatest anatomical changes in the ripening seeds occurred in the sarcotesta and in the nucellar layers. Maturation of the surface structures was essentially slower than could have been interpreted by the size of the embryo and responded clearly to the disturbance of photoperiod. Accumulation of phenolic substances and degeneration of cells, particularly at the chalazal region, advanced faster in the light-treated than in the control seeds up to mid-September. The ripening effect of the altered photoperiod diminished, however, after mid-September. This was also confirmed by the brown colour of the seed coat getting darker only in the control seeds at the end of the test period. Consequently, fully ripe structures were first found about a fortnight earlier in the control than in the light-treated seeds. The coincidental advancement of the anatomical potential examined by the X-ray method supported the role of the surface structures on the anatomical maturity of pine seeds and the timing of cone collecting.