Solutes Contributing to Osmotic Adjustment in Cultured Plant Cells Adapted to Water Stress

Abstract

Osmotic adjustment was studied in cultured cells of tomato (Lycopersicon esculentum Mill cv VFNT-Cherry) adapted to different levels of external water potential ranging from -4 bar to -28 bar. The intracellular concentrations of reducing sugars, total free amino acids, proline, malate, citrate, quaternary ammonium compounds, K@, NO3-, Na', and Cl1 increased with decreasing external water potential. At any given level of adaptation, the maximum contribution to osmotic potential was from reducing sugars followed by potassium ions. The sucrose levels in the cells were 3-to 8-fold lower than reducing sugar levels and did not increase beyond those observed in cells adapted to -16 bar water potential. Concentrations of total free amino acids were 4-to 5-fold higher in adapted cells. Soluble protein levels declined in the adapted cell lines, but the total reduced nitrogen was not significantly different after adaptation. Uptake of nitrogen (as NH4' or NO3-) from the media was similar for adapted and unadapted cells. Although the level of quaternary ammonium compounds was higher in the nonadapted cells than that of free proline, free proline increased as much as 500-fold compared to only a 2-to 3-fold increase observed for quaternary ammonium compounds. Although osmotic adjustment after adaptation was substantial (up to -36 bar), fresh weight (volume increase) was restricted by as much as 50% in the adapted cells. Altered metabolite partitioning was evidenced by an increase in the soluble sugars and soluble nitrogen in adapted cells which occurred at the expense of incorporation of sugar into cell walls and nitrogen into protein. Data indicate that the relative importance of a given solute to osmotic adjustment may change depending on the level of adaptation.

Physiological Changes in Cultured Sorghum Cells in Response to Induced Water Stress

“…Accumulation of solutes in response to water deficits has been observed in leaves ofsorghum (2,8,9). A similar phenomenon was also observed when plant cells were cultured under conditions of induced water stress using PEG (5). It was further shown that PEG itself did not contribute significantly to the osmotic adjustment (4).…”

“…A correlation 5 10 for proline as an osmoprotectant. Proline as a useful selection criterion for drought tolerance has not stood the test in plant breeding programs in barley (6) and rapeseed (13).…”

“…PEG, mol wt 8000, was added to the growth medium at concentrations of 5,10,15,20 Amino Acid Analysis. Between 20 and 50 mg ofthe lyophilized tissue was extracted with 10 ml hot 80% ethanol, followed by two washings with 5 ml ethanol each.…”

Adaptation of Tobacco Cells to NaCl

“…10). It is possible that the large absolute values are due in part to the limitations of the plasmometric technique for the determination of osmotic potentials (15).…”

Physiological response of oil palm interspecific hybrids (Elaeis oleifera H.B.K. Cortes versus Elaeis guineensis Jacq.) to water deficit

“…Thus, increasing root absorption capacity per surface unit to favor the partitioning of assimilates towards this organ is a tolerance response to water deficit (Ryser, 2006;Polanía et al, 2009), mainly in oil palm ). However, under severe water deficit conditions, the 'U1937' hybrid decreased its overall water potential, as an active response to the accumulation of reducing and total sugars in leaf cells (decrease in osmotic potential), which allowed the plants to maintain their flow of water through the roots and reduce its loss through the stomatal chamber, a response that some authors consider as an indicator of growth or survival (tolerance) to water deficit (Handa et al, 1983;Gomes and Prado, 2007;López et al, 2009). This type of osmotic adjustment under water deficit conditions has been reported in leaves and in other organs of sorghum, rice, potatoes, corn, wheat (Silva et al, 2007), pine (López et al, 2009), and oil palm .…”