Cryopreservation of Pistacia spp. seeds by dehydration and one-step freezing

Cryopreservation protocols by dehydration and one-step freezing were developed for seeds from three Pistacia species, i.e., P. vera, P. terebinthus and P. lentiscus, which were characterised by different initial germination percentages (100%, 17% and 81%, respectively). In P. vera, a maximum of 90% germination was obtained following 8 hours drying in silica gel (corresponding to 11.7% moisture content on a FW basis) and direct immersion in LN. In P. terebinthus and P. lentiscus, shorter periods of dehydration (1 hour and 15 min, respectively) were sufficient to reduce their moisture content to about 20%, which resulted in peak seed germination percentages from cryostorage of 16% and 47%, respectively. Following cryopreservation, the seeds germinated better on semi-solid MS medium, than on cotton wool wetted with dH(2)O or liquid MS medium. Finally, in P. vera and P. lentiscus, high and significant correlation coefficients were obtained between the TTC viability test and seed germinability after recovery from LN, provided that seeds which were considered positive in the test showed completely or partially red embryonic axes coupled to completely red cotyledons.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.