Adaptive anatomical structure for nastic movement in Mimosa pudica L.

In order to study the adaptive anatomical structures during nastic movement of Mimosa pudica L., anatomical structures of main pulvinus, common petioles, rachis and leaflets were compared with Albizia julibrissin Durazz. (taken as control). The anatomical structures of main pulvinus and common petiole of M. pudica were different from that of A. julibrissin. Upon stimuliti, the protoplast volume of M. pudica in the lower cortical parenchyma cells become smaller than that in upper ones, a feature seldom found in A. julibrissin. There were found many reticulate lacunas on the two side of adaxial petiole of M. pudica, but nil in A. julibrissin. Similarly some ill developed lacunas were found in the pulvinus of rachis and leaflet of M. pudica, but absent in A. julibrissin. It appears that reticulate lacunas in common petiole of M. pudica are responsible for its strong nastic movement. The main sensitivity position lies at the base of common petiole, where the lower cortex is more sensitive than the upper cortex, and the ordinal sensitivity positions are rachis and leaflets. DOI: http://dx.doi.org/10.3329/bjb.v42i1.15876 Bangladesh J. Bot. 42(1): 131-137, 2013 (June)

Aquaporins in the plasma membrane of leaf callus protoplasts of Actinidia deliciosa var. deliciosa cv. Hayward

The water transport activity of Actinidia deliciosa protoplasts was determined using a cell imaging system. Results showed that the protoplast volume increased swiftly when placed in a hypoton-ic medium, and also increased with an increase in medium osmotic gradients. The osmotic water permeability coefficient (Pf) values were 0.118 × 10–3, 0.121 × 10–3, and 0.133 × 10–3 cm s–1 when the osmotic gradients were 75, 100, and 125 mosmol, respectively. The water transport activity of protoplas-ts could be inhibited by HgCl2 and stimulated by amphotericin B. Moreover, ZnCl2 and ZnSO4 had a significant inhibitory effect on the water transport activity of the protoplasts. Our results indicate that the Actinidia deliciosa protoplasts had properties typical of aquaporins, suggesting that aquaporins were present at the plasma membrane.

Three-dimensional quantitative description of symbiont ultrastructure within the algal layer oftwo members of the lichen family Umbilicariaceae

The ultrastructure of the symbionts within the algal layer of Lasallia hispamca and Umbilicaria spodochroa has been investigated by applying stereological techniques to quantify cellular organelles and structures. The stereological parameters calculated were volume density (Vv) and surface density (Sv). To obtain these parameters for each cellular structure, a systematic sampling of photographic fields of the algal layer for each sample was utilized.Significant differences between the two lichen species with respect to both symbionts were observed. The cellular structures of the photobiont that differed the most between the two lichen species were the chloroplast, which differed by 15°0, in the Vv values and 25°0, in the Sv values, the pyrenoid (as a whole and in the diameter of pyrenoglobuli) and the mitochondria. With respect to the mycobiont, the vacuolar apparatus was of great importance in characterizing the two species, as was to a lesser extent the protoplast volume occupied by concentric bodies.

Evidence for nonstomatal inhibition of net photosynthesis in rapidly dehydrated shoots of Populus

Results are presented on the decline of net photosynthesis during the application of rapid water stress to excised shoots of different Populus L. clones. Six clones were selected from the species Populustrichocarpa Torr. & Gray, Populusdeltoides Bartr., and from the hybrid Populustrichocarpa × Populusdeltoides, taking into account the differences in stomatal behaviour between and within these species. The two most productive P. trichocarpa clones and the hybrid clone, characterized by a reduced ability to close stomata during leaf desiccation, showed, nevertheless, a sharp reduction of net photosynthesis at water potentials lower than −1.5 MPa. In contrast, the inhibition of net assimilation in the P. deltoides clone, caused by water stress, was accompanied by a reduction in stomatal conductance. In all studied clones the decrease in net photosynthetic rate followed closely the point of turgor loss of the leaves, indicating a possible relationship between nonstomatal inhibition of photosynthesis and protoplast volume shrinkage.