Mucilages and polysaccharides in Ziziphus species (Rhamnaceae): localization, composition and physiological roles during drought‐stress
Open Access
- 1 January 2002
- journal article
- Published by Oxford University Press (OUP) in Journal of Experimental Botany
- Vol. 53 (366), 131-138
- https://doi.org/10.1093/jexbot/53.366.131
Abstract
The drought‐tolerant tree species Ziziphus mauritiana Lamk. and Z. rotundifolia Lamk. were shown to have similar high mucilage concentrations (7–10% dry weight) in their leaves, with large numbers of mucilage‐containing cells in the upper epidermis and extracellular mucilage‐containing cavities in the leaf veins and stem cortex. The main sugar constituents of the water‐soluble mucilage extract were rhamnose, glucose and galactose. During drought‐stress in two independent studies, foliar mucilage content was unaffected in both species, but glucose and starch contents declined significantly in crude mucilage extracts from droughted leaves. Enzymatic hydrolysis of the mucilage extract using α‐amylase and amyloglucosidase released glucose, indicating that a mucilage‐associated water‐soluble glucan, with α‐1,4‐ and α‐1,6‐linkages, may exist which was extracted together with the mucilage. From the current data, it is not possible to localize the glucan to determine whether or not it is associated with mucilage‐containing cells. Data from pressure–volume analyses of drought‐stressed and control leaves showed that, in line with their similar mucilage contents, the relative leaf capacitance isotherm (change in relative water content per unit change in water potential) was similar in both species. During drought‐stress, reduced relative capacitance resulted from osmotic adjustment and decreased wall elasticity. Data suggest that in Ziziphus leaves, intracellular mucilages play no part in buffering leaf water status during progressive drought. In Ziziphus species, growing in environments with erratic rainfall, the primary role of foliar mucilage and glucans, rather than as hydraulic capacitors, may be as sources for the remobilization of solutes for osmotic adjustment, thus enabling more effective water uptake and assimilate redistribution into roots and stems prior to defoliation as the drought‐stress intensified.Keywords
This publication has 31 references indexed in Scilit:
- Physiological and morphological adaptations of the fruit tree Ziziphus rotundifolia in response to progressive drought stressTree Physiology, 2001
- Contrasting adaptations to drought stress in field-grown Ziziphus mauritiana and Prunus persica trees: water relations, osmotic adjustment and carbon isotope compositionFunctional Plant Biology, 2000
- The role of solute accumulation, osmotic adjustment and changes in cell wall elasticity in drought tolerance in Ziziphus mauritiana (Lamk.)Journal of Experimental Botany, 1998
- Field comparisons of photosynthesis and leaf conductance in Ziziphus mauritiana and other fruit tree species in ZimbabweTrees, 1997
- The mucilaginous polysaccharide material isolated from ruredzo (Dicerocaryum zanguebarium)Food Chemistry, 1993
- The development of mucilage cells inHibiscus schizopetalusActa Botanica Neerlandica, 1992
- Host-Pathogen InteractionsPlant Physiology, 1986
- Structural Features ofPlantago lanceolata MucilagePlanta Medica, 1985
- Form and function of arabinogalactans and arabinogalactan-proteinsPhytochemistry, 1979
- Plant Microtechnique: Some Principles and New MethodsAmerican Journal of Botany, 1968