Storage protein mobilization and thiol protease up-regulation by solid matrix priming in loblolly pine (Pinus taeda) seed embryos

Experiments were conducted to investigate physiological mechanisms of solid matrix priming (SMP) on germination enhancement of loblolly pine (Pinus taeda) seeds. During SMP, osmotic potential in the embryo decreased by 0.65 MPa, concentration of crystalloid proteins decreased to 62% and concentrations of buffer soluble proteins and free amino acids increased by 22% and by 166%, respectively. Observations under an electron microscope demonstrated protein bodies in the embryo were mobilized. Inhibitor analysis indicated thiol protease was the dominant enzyme among endopiptidases to degrade the reserved proteins. A fragment of thiol protease was cloned from the primed seed embryos and it has high identities to those thiol proteases responsive to water stress. RNA get blot analysis showed a 1.5 kb thiol protease gene was up-regulated by SMP. Treatment with E64, a thiol protease inhibitor, negated SMP effects on germination performance, water potentials and protein profiles. Based on the experimental results, reserve protein mobilization induced by SMP in the embryo before radicle emergence might be one of the mechanisms to enhance germination in loblolly pine seeds.

Effect of growing site, moisture stress and seed size on viability and dormancy of Sporobolus pyramidalis (giant rats tail grass) seed

Sporobolus pyramidalis P. Beauv (giant rats tail grass) is a serious agricultural and environmental weed in tropical and subtropical areas of Australia. Infestations of this unpalatable plant reduce the productivity of pastures and the profitability of industries dependent on grazing animals. This paper reports a series of studies undertaken to assist in the development of control strategies for this species. In particular, these studies measured the viability and dormancy status of fresh seed of S. pyramidalis and the decline of dormancy with time. Variability in these characteristics was determined in seeds collected from several sites within south-east Queensland. The effect of moisture availability during the inflorescence and seed production phases on seed viability and dormancy was also determined. The dormancy of freshly collected seed from several sites ranged from 15 to 95%, but decreased to negligible levels after 4-6 months. Seeds that matured under conditions of high moisture availability were initially more dormant than seeds matured where moisture was less readily available. The proportion of viable seeds was significantly lower in smaller than larger seeds even though viability for all seed sizes exceeded 90%. This study has shown that seed of S. pyramidalis generally has high viability with a large proportion of the seed germinable soon after maturity.