Histological observation and scanning electron microscopy analyses in Dendrobium Bobby Messina indicates the cellular process of cryopreserved protocorm-like bodies (PLBs) was different comparative to non-cryopreserved PLBs. The cellular process was not only modified by the freezing and thawing effect but also due to the dehydration process itself during the cryopreservation procedure. Histological observation in Dendrobium Bobby Messina in encapsulation-dehydration method indicated that the degree of plasmolysis causes more cellular changes to the cryopreserved PLBs comparative to non-cryopreserved and stock culture PLBs. These results revealed higher amount of homogenous cell population and denser cytoplasm in cryopreserved PLBs. Histological analysis also revealed more voluminous nucleus in cryopreserved PLBs comparative to non-cryopreserved PLBs and PLBs stock culture. In contrast, scanning electron microscope analysis showed severe damages in cryopreserved PLBs and non-cryopreserved PLBs comparative to the PLBs stock culture which in return could be the possible reason of no regrowth in encapsulation-dehydration method. Damages incurred were on top part, side part, and at the stomata of the PLBs. Histological observation and scanning electron microscopy analyses in Dendrobium Bobby Messina indicates that the degree of plasmolysis causes changes in the cellular process of PLBs from cryopreserved PLBs was different comparative to non-cryopreserved PLBs.
The effects of sucrose preculture duration and loading treatment on tolerance of Garcinia cowa shoot tips to cryopreservation using the PVS2 vitrification solution were investigated. Ultrastructural changes in meristematic cells at the end of the preculture and loading steps were followed in an attempt to understand the effects of these treatments on structural changes in cell membranes and organelles. Increasing preculture duration on 0.3 M sucrose medium from 0 to 3 days enhanced tolerance to PVS2 solution from 5.6 percent (no preculture) to 49.2 percent (3-day preculture). However, no survival was observed after cryopreservation. Examination of meristematic cells by transmission electron microscopy revealed the progressive accumulation of an electron-dense substance in line with increasing exposure durations to 0.3 M sucrose preculture. Treatment with a loading solution (2 M glycerol + 0.4 M sucrose) decreased tolerance of shoot tips to PVS2 vitrification solution and had a deleterious effect on the ultrastructure of G. cowa meristematic cells. This study suggests that G. cowa meristematic cells may lose their structural integrity due to exposure to glycerol present in the loading solution at a 2 M concentration, either due to its high osmotic potential, or due to its cytotoxicity.
Dendrobium sonia-28 is a popular orchid hybrid due to its flowering recurrence and dense inflorescences. Unfortunately, it is being decimated by fungal diseases, especially those caused by Fusarium proliferatum. In this study, selection of F. proliferatum-tolerant protocorm-like bodies (PLBs) was carried out by assessing the effects of differing concentrations of fusaric acid (FA). PLBs were cultured on Murashige and Skoog (MS) medium supplemented with 0.05 to 0.2 millimolar (mM) concentrations of FA. Higher concentrations of FA increased mortality of PLBs and reduced their growth. The survival rate for 0.05 mM FA was 20 % but only 1 % at the highest dose of 0.2 mM. Additionally, two different size ranges of PLBs were investigated, and growth increased more at lower FA concentrations for larger PLBs, whilst the growth rate of smaller PLBs was inhibited at an FA concentration of 0.2 mM. Histological examination using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses disclosed severe cell wall and organelle damage, as well as stomatal closure in PLBs treated with the high FA concentrations. Reductions in plantlet growth were much greater at the highest concentrations of FA. Some randomly amplified polymorphic DNA (RAPD) markers clearly discriminated between selected and non-selected variants of Dendrobium sonia-28, showing different banding patterns for each FA concentration and specific bands for selected and control plants.