Stachyose Synthesis in Source Leaf Tissues of the CAM Plant Xerosicyos danguyi H. Humb.

Abstract

MATERIALS AND METHODS Leaf tissues from Xerosicyos danguyi H. Humb., a succulent member of the Cucurbitaceae, were found to possess both galactinol synthase activity and the capacity for photosynthetic production of stachyose, the phloem transport oligosaccharide common to other nonsucculent cucurbits. The amounts of stachyose isolated from leaf tissues, and the extractable activity of galactinol synthase, were somewhat higher in leaf tissues obtained from plants operating in the Crassulacean acid metabolism (CAM) mode (well watered plants) compared to leaf tissues from plants operating in the CAM-idling mode (water-stressed plants). In contrast, in leaf discs, the photosynthetic incorporation of label into stachyose foliowing pulse labeling with 14C02 was similar for stressed and for nonstressed tissues. Stachyose could be extracted from, and was synthesized photosynthetically by, leaf discs which contained no vascular tissues, indicating that synthesis of stachyose can occur in photosynthetic mesophyll cells of Xerosicyos.

Different ratios of sucrose/raffinose-induced membrane depolarizations in the mesophyll of species with symplasmic (Catharanthus roseus, Ocimum basilicum) or apoplasmic (Impatiens walleriana, Vicia faba) minor-vein configurations

“…The data provide physiological evidence -supplem e n t a r y to that obtained with p-chloromercuribenzenesulfonic acid treatments , m i c r o a u t o r a d i o g r a p h y (Eschrich and F r o m m 1994) and m e a s u r e m e n t s of n o n -s t r u c t u r a l sugars (K6rner et al 1995) -in favour of two modes of phloem loading and the association between the minor-vein configuration and the mode of loading. Furthermore, the results are consistent with the reported occurrence of galactosyl oligosaccharides in the mesophyll of symplasmic species (Madore et al 1988; Beebe and T u r g e o n 1992).…”

“…The size exclusion limit of the plasmodesmata between bundle sheath and intermediary cell would allow the passage of mono-and disaccharides to the intermediary cell, but prevent the backflow of the oligosaccharides to the bundle sheath (Turgeon 1991). Seemingly inconsistent with the 'polymerization trap' model is the reported occurrence of galactosyl oligosaccharides in the mesophyll (Madore and Webb 1982;Madore et al 1988), but this is interpreted as being a temporary storage pool (Beebe and Turgeon 1992;Madore 1992). An alternative postulate for the mechanism of symplasmic phloem loading claims that the oligosaccharides are chiefly produced in the mesophyll and loaded there into a vacuolar-vesicular network extending from the mesophyll to the intermediary cells across the plasm o d e s m a t a (Gamalei et al 1994).…”

Stachyose and mannitol transport in olive (Olea europaea L.)

“…Several recent studies have closely examined the sugar-synthesis and transport patterns associated with species which export raffinose oligosaccharides (Madore and Webb 1981;Madore et al 1988;Wiesberg et al 1988 ;Madore 1990;Turgeon and Gowan 1990;Turgeon and Beebe 1991;Turgeon and Gowan 1992;Madore 1992). It has been speculated that phloem loading in these species may be entirely symplastic (Madore and Webb 1981;Schmitz et al 1987;Turgeon and Gowan 1990;Gamalei 1991;Turgeon and Beebe 1991;Turgeon and Gowan 1992;, based largely on ultrastructural evidence obtained from the specialized companion cells (intermediary cells) in the minor veins.…”

Water Deficit Effects on Raffinose Family Oligosaccharide Metabolism in Coleus

“…Samples were stored frozen at Ϫ20°C until analysis. Soluble sugars were extracted with 80% (v/v) ethanol, deionized, and analyzed by HPLC (Sugar-Pak I column, Waters, Milford, MA), essentially as described previously (Madore et al, 1988). Starch remaining in the extracted discs was digested with amyloglucosidase and released Glc was quantified spectrophotometrically using a commercially available Glc detection kit (HK 20, Sigma, St. Louis) as described previously (Madore, 1990).…”