Biochemical Changes During Osmopriming of Leek Seeds

Osmotic priming treatments reduced both the mean time to germination and the spread of germination for two leek seed-lots of high viability but differing vigour. In addition the differences in germination performance between these two seed-lots was abolished by the priming treatments. In the unprimed seed-lots, differences in germination performance were reflected in differences in rates of protein biosynthesis in leek embryo tissue during germination. Osmopriming treatments abolished these differences upon subsequent germination of osmotically primed seed and furthermore induced high levels of protein biosynthesis in embryo tissue. DNA synthesis was detectable in leek embryos during the priming period in the absence of any cell division and was followed by a five-fold increase in the rate of DNA synthesis in embryo tissue upon germination following priming at which time the rates of DNA synthesis in these leek embryos was significantly greater than that found at any time over the first 4 d of germination in embryos of unprimed leek seeds. The increases in rates of both protein and DNA synthesis observed upon germination of primed seed occurred only after a 6–12 h lag period during which time there is little increase in these rates above those found at the end of priming Analysis of nucleotide and nucleotide sugar levels in leek embryos both during and after priming showed that only traces of GTP and CTP and low levels of ATP and UTP were present in embryos during priming. After a 6 h lag period following the end of priming these levels increased sharply, probably via de novo synthesis. A similar pattern was found for UDP glucose levels during priming and subsequent germination. These results indicate that there is considerable biochemical activity during priming and that the significant benefits in germination performance of primed leek seeds is accompanied by marked increases in protein, DNA and nucleotide biosynthesis after a lag period of 6–12 h following the end of the priming period