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The leaf is the main organ of the vegetative body of tank epiphytic bromeliads, which may be subdivided into apical and basal parts. Little is known about the existence of morphological, anatomical or physiological differences between these two leaf portions. The objective of this study was to verify the existence of a differential capacity to assimilate nitrogen from urea between basal and apical leaf portions of Vriesea gigantea, a tank epiphytic bromeliad. Plants were cultivated in vitro in the presence of 5 mM urea for 15 days. During this period, the activities of the enzymes glutamine synthetase (GS, EC 6.3.1.2) and NADH-dependent glutamate dehydrogenase (NADH-GDH, EC 1.4.1.2) were quantified, as well as the densities of trichomes and stomata found at the leaf surface of both regions. The highest activities of GS and NADH-GDH were always detected at the top portion, and on the 3rd day of in vitro cultivation an increase in these activities was detected. An inverse correlation between number of trichomes and stomata in these two leaf portions was verified: the top region presented 30% less trichomes and twice as many stomata as the basal region. This suggests that the upper region of the leaf may be preferentially involved with the assimilation of nitrogen from urea via GS and NADH-GDH, whereas the basal region may be involved with its absorption. This is the first study to report that ammonium assimilation may take place preferentially in a specific portion of tank-forming bromeliad leaves.

Water availability modulated CAM expression in an organ-compartmented manner in both orchids studied. As distinct regions of the same orchid could perform different photosynthetic pathways and variable degrees of CAM expression depending on the water availability, more attention should be addressed to this in future studies concerning the abundance of CAM plants.

The stomach of the rat undergoes extensive changes during the formation and maturation of gastric glands. The presence of transforming growth factor beta (TGF␤) in rat milk and in the gastrointestinal tract of pups may suggest its role in this process. The current study evaluated the in vivo dynamic expression and distribution of TGF␤1, ␤2, ␤3 and their receptors T␤RI and T␤RII in the gastric epithelium of 20-day fetal rats and 1-, 14-, 21-, and 30-day-old pups. Immunohistochemistry was used to detect the proteins, and staining was classified according to intensity and cell type. The results showed that the gastric epithelium expresses TGF␤ isoforms and receptors throughout development. We found that immunoreactivity paralleled the appearance of differentiated cells, such that surface mucous cells were the first to be immunostained and chief cells were the last. The intensity of reactions followed this same pattern, showing that the expression of TGF␤ isoforms spread along the gland with growth. Of interest, the highest apparent activity of TGF␤ was observed from 21 days onward, a period that is concomitant with weaning and maturation of most gastric cell types. In addition, surface mucous cells were strongly labeled at the basal cytoplasm at 14 days, suggesting an interaction with the connective tissue. In conclusion, the dynamic expression of TGF␤1, ␤2, ␤3, and T␤RI and T␤RII through stomach development suggests significant paracrine and autocrine roles for this growth factor. We propose that temporal and spatial differences may be regulated by dietary changes, which in turn control cell proliferation and differentiation in the gastric epithelium. Developmental Dynamics 227:450 -457, 2003.

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