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

Abstract

Abstract. Source leaves of Olea europea L. (olive) were photosynthetically labelled with 14C02 and then transferred to 20 mM EDTA solutions to allow exudation of phloem sap. Label in phloem sap was recovered predominantly as stachyose (50 60% of the total label) while only small amounts of label were recovered in the sugar alcohol mannitol (less than 5%). In contrast, in leaf tissues stachyose accounted for only 5% of the total leaf label while mannitol accounted for 30%. Vacuum-infiltration of exuding leaves with 1 mM p-chloromercuriphenylsulfonic acid had no effect on subsequent exudation or on the distribution of label in stachyose or mannitol in either leaf tissues or phloem exudates. In contrast, a similar treatment inhibited the uptake of exogenously supplied [~4C]stachyose and [14C]sucrose into leaf discs. Following short-term pulse-chase experiments with ~4CO2 (15 s pulse, 5 s 20 min chase), sucrose, mannitol and galactinol were rapidly labelled within the first 2 min following the pulse. Stachyose and raffinose, on the other hand, were not appreciably labelled until 10 min after the pulse. Taken together, the data indicate that phloem loading of raffinose oligosaccharides or of mannitol may not require an apoplastic step. Additionally, it appears that there may be a spatial separation of the synthesis of these sugars within the leaf, with mannitol synthesis occurring within the photosynthetic mesophyll tissues and raffinose oligosaccharide synthesis occurring closer to, and probably within, the minor veins.

Physio-Biochemical Responses of Oil Palm (Elaeis guineensisJacq.) Seedlings to Mannitol- and Polyethylene Glycol-Induced Iso-Osmotic Stresses

“…Similar results in the overall growth performance have been recorded in maize coleoptiles (Hohl and Schopfer, 1991). Osmotic stress induced by PEG, especially high-molecular weight PEG (MW>1000) has been reported to limit water uptake and O 2 -disolution (Lawlor, 1970;Janes, 1974), whereas mannitol has been used only as an osmoticum with low absorption rate by the root tissues of plants (<5% radioactive labeling) (Smith and Smith, 1973;Flora and Madore, 1993;Vítová et al, 2002).…”

Characterization of Sicilian Olive Genotypes by Multivariate Analysis of Leaf and Fruit Chemical and Morphological Properties

“…There was, in fact, no correlation among mannitol contents of various tissues, meaning that different genotypes may follow distinct strategies in the partitioning of mannitol among organs. Also, there was no significant difference in average mannitol content between leaf and bark, which would be in contrast with previous observations showing a totally symplastic pathway for mannitol phloem loading in olive (Flora & Madore, 1993) and in favor of more recent findings supporting a dual (symplastic and apoplastic) loading system (Conde et al, 2008). In addition to this, significant amounts of mannitol may be stored in parenchyma cells of shoots and may have contributed to the high mannitol levels observed in our bark tissues.…”

Phloem Loading Strategies in Three Plant Species That Transport Sugar Alcohols

“…PCMBS severely inhibits the function of Suc transporters. Unfortunately, sugar alcohol transporters tested to date are not affected by PCMBS (Flora and Madore, 1993;Noiraud et al, 2001a;Gao et al, 2003;RamspergerGleixner et al, 2004;Watari et al, 2004;Juchaux-Cachau et al, 2007), with the exception of two sorbitol transporters (Ramsperger-Gleixner et al, 2004;McQueen et al, 2005).…”