Apoplastic Sugars, Fructans, Fructan Exohydrolase, and Invertase in Winter Oat: Responses to Second-Phase Cold Hardening

Abstract

Changes in apoplastic carbohydrate concentrations and activities of carbohydrate-degrading enzymes were determined in crown tissues of oat (Avena sativa L., cv Wintok) during cold hardening. During second-phase hardening (؊3°C for 3 d) levels of fructan, sucrose, glucose, and fructose in the apoplast increased significantly above that in nonhardened and first-phase-hardened plants. The extent of the increase in apoplastic fructan during second-phase hardening varied with the degree of fructan polymerization (DP) (e.g. DP3 and DP4 increased to a greater extent than DP7 and DP > 7). Activities of invertase and fructan exohydrolase in the crown apoplast increased approximately 4-fold over nonhardened and first-phase-hardened plants. Apoplastic fluid extracted from nonhardened, first-phase-hardened, and second-phase-hardened crown tissues had low levels, of symplastic contamination, as determined by malate dehydrogenase activity. The significance of these results in relation to increases in freezing tolerance from second-phase hardening is discussed.Cold-hardening winter cereals such as rye (Secale cereale), wheat (Triticum aestivum), barley (Hordeum vulgare), and oat (Avena sativa) is generally accomplished by exposure to temperatures just above freezing. As early as 1935, Tumenov (cited by Trunova, 1965) reported that an additional phase of hardening by exposure of cold-hardened plants to nonlethal, below-freezing temperatures resulted in significant increases in cold hardiness. Tumenov called this 2PH. With a 2PH treatment, Trunova (1965) and Siminovich (cited by Steponkus, 1978) induced an increase in freezing tolerance of wheat significantly beyond that achieved from cold hardening above freezing (1PH). Olien (1984) reported similar results in rye and barley, and reported a decrease in the LT 50 of oats from Ϫ13°C with 1PH only to Ϫ18°C after a 3-d 2PH period at Ϫ3°C.After 2PH Trunova (1965) found decreased levels of fructan and increased levels of Glc, Fru, and Suc in whole crown tissue of wheat. He suggested that the sugar increase during 2PH was providing osmotic protection to cells in the over-wintering organ (crown) of the plant. Olien (1984), using a perfusion technique, reported an increase in apoplastic sugars during 2PH and suggested that these sugars helped prevent adhesion of ice to critical cellular tissue during freezing.In the present study we wanted to determine the percent distribution of fructan exohydrolase and invertase in the apoplast and symplast of oat crowns, and what the effect of 1PH and 2PH would be on their activities in the respective locations. Additionally, we wanted to determine if fructan was present in the apoplast and the effect of cold hardening on its presence. Finally, we wanted to re-examine the effect of cold hardening on simple sugar levels in the apoplast using a different technique than that used by Olien (1984). MATERIALS AND METHODS Plant CultureSeeds of the oat (Avena sativa L.) cv Wintok were planted in Scotts Metromix 220 1 (Scotts-Sierra Horticultural Products Co...

Spatio-Temporal Dynamics of Fructan Metabolism in Developing Barley Grains

“…In general, fructans are thought to be localized in the vacuole (Pollock et al, 1996;Vijn and Smeekens, 1999), although an apoplastic localization of fructans and 1-FEH activity was reported (Livingston and Henson, 1998;Kawakami et al, 2005). There are two possible explanations for tissue specificity and unexpected apoplastic localization in developing barley grains.…”

“…In addition, the fructans may act as osmoregulants and thus exert control over the cell expansion process (Schnyder et al, 1993). Such regulatory function was also elaborated for cold and drought hardening (Livingston and Henson, 1998;Valluru and Van den Ende, 2008;Livingston et al, 2009). …”

Systemic Cold Stress Adaptation of Chlamydomonas reinhardtii

“…5B). Other general responses to cold-induced membrane damage are an increased accumulation of cryoprotectants (12,13,15); LEA, cold-and heat-shock proteins (HSP), which participate in membrane protection and refolding of denatured proteins (88,89); and the accumulation of antioxidants mostly at chloroplast level (90,91).…”

“…To avoid these effects that may affect all of the metabolic pathways and withstand low temperatures, the cells should accomplish numerous physiological, biochemical and molecular changes. This process, called acclimation, is not described in Chlamydomonas whereas extensively studied in higher plants (7,8): Stressrelated genes are induced (9,10), antioxidative mechanisms (11), cryoprotectant osmolytes and proteins are increased (12,13), lipid composition is altered and membranes are stabilized (14,15) whereas photosynthesis (16), nutrient absorption, and growth are decreased (17).…”

Biochemical and Physicochemical Background of Mammalian Androgen Activity in Winter Wheat Exposed to Low Temperature

“…Lower contents of two fructans: nystose (three units of fructose + one glucose) and kestose (two units of fructose + one glucose) in the AN-treated plants (comparing to control) may then result from lower accumulation of sucrose. Fructans serve as osmoprotectants and stabilize cell membranes by inserting polysaccharides into the lipid head region of the membrane (Hendry 1993;Livingston and Henson 1998). Due to the protective properties of fructans against abiotic stress, a decrease in their content may even weaken anti-stress mechanisms of the cold-exposed plants.…”