Freezing Tolerance of Citrus, Spinach, and Petunia Leaf Tissue

Abstract

Seasonal variations in freezing tolerance, water content, water and osmotic potential, and levels of soluble sugars of leaves of field-grown Valencia orange (Citrus sinensis) trees were studied to determine the ability of citrus trees to cold acclimate under natural conditions. Controlled environmental studies of young potted citrus trees, spinach (Spinacia pleracea), and petunia (Petunia hybrids) were carried out to study the water relations during cold acclimation under less variable conditions. During the coolest weeks of the winter, leaf water content and osmotic potential of field-grown trees decreased about 20 to 25%, while soluble sugars increased by 100%. At the same time, freezing tolerance increased from lethal temperature for 50% (LTso) of -2.8 to -3.80C. In contrast, citrus leaves cold acclimated at a constant 100C in growth chambers were freezing tolerant to about -60C. The calculated freezing induced cellular dehydration at the LT5o remained relatively constant for field-grown leaves throughout the year, but increased for leaves of plants cold acclimated at 100C in a controlled environment. Spinach leaves cold acclimated at 50C tolerated increased cellular dehydration compared to nonacclimated leaves. Cold acclimated petunia leaves increased in freezing tolerance by decreasing osmotic potential, but had no capacity to change cellular dehydration sensitivity. The result suggest that two cold acclimation mechanisms are involved in both citrus and spinach leaves and only one in petunia leaves. The common mechanism in all three species tested was a minor increase in tolerance (about -10C) resulting from low temperature induced osmotic adjustment, and the second in citrus and spinach was a noncolligative mechanism that increased the cellular resistance to freeze hydration.During extracellular freezing, ice first forms in the dilute apoplastic solution and a water potential gradient is established between the extracellular ice crystal and the intracellular liquid water. The lower water potential of ice as compared to that of liquid cellular water at the same temperature will cause liquid water to move from the cell to the extracellular ice (19). This process, depending on the temperature and concentration of the cell sap imposes a dehydration stress 'Part of this work was supported by a U.S. Department of Agriculture competitive research grant 85-CRCR-1-1649. University of Florida Agricultural Experiment Station Technical paper 8889. on the cell. When the cellular water potential of the partially dehydrated cell equals that of the extracellular ice, an equilibrium is established and further dehydration will not occur provided the temperature remains constant (15,23). If the temperature further declines or increases, water will flow out of or back into the cell. During such equilibrium freezing a tissue can behave either as an ideal solution or as a nonideal solution (15,23). In nonideal equilibrium freezing, negative wall pressure is believed to reduce the degree of cell dehydration and solute co...

Cryopreservation of spores of vesicular–arbuscular mycorrhizal fungi*

“…Cryoprotective agents work by several means. Some can permeate cells and may act as 'noninjurious solutes', increasing bound water and decreasing freeze dehydration at a given temperature (Levitt, 1980, p. 236;Yelenosky & Guy, 1989). Also, cryoprotectants may be impermeable compounds and may act as hypertonic solutions, drawing water out of cells and thereby providing a measure of freeze protection via dehydration.…”

Alterations in Water Status, Endogenous Abscisic Acid Content, and Expression of rab18 Gene during the Development of Freezing Tolerance in Arabidopsis thaliana

“…This adjustment is achieved by accumulation of compatible osmolytes and results in the retention of turgor and the capacity for cell elongation at low water potential (Levitt, 1980b). Various degrees of osmotic adjustment have been reported in herbaceous plants during cold acclimation (Levitt, 1980a;Chen and Li, 1982;Lalk and Dorffling, 1985;Sakai and Larcher, 1987;Yelenosky and Guy, 1989), but more importantly, cold acclimation-induced osmolytes such as sugars and amino acids might help the plant to survive freeze-induced cellular dehydration stress by acting as noncolligative cryo-or osmoprotectants (Yelenosky and Guy, 1989).…”

“…ABA (Chen et al, 1983;Chen and Gusta, 1983;Orr et al, 1986;Ling et al, 1989;Lee and Chen, 1993). Adaptation of a plant to survive extracellular ice formation is mainly adaptation to freeze-induced cellular dehydration (Levitt, 1980a;Sakai and Larcher, 1987;Steponkus and Lynch, 1989;Yelenosky and Guy, 1989;Steponkus, 1990). Numerous physiological alterations, including plasma membrane composition, leaf water status, phytohormone level, and gene expression have been correlated with this adaptation process (Levitt, 1980a;Sakai and Larcher, 1987;Steponkus and Lynch, 1989;Guy, 1990;Steponkus, 1990;Thomashow, 1990).…”

Indicateurs physiologiques pour le screening de génotypes de tournesol tolérants aux basses températures associées au semis précoce

“…Ces sucres permettent de réguler la pression osmotique et de diminuer le point de congélation de la cellule (Koster et Lynch, 1992). Les sucres (saccharose, glucose, fructose) ne sont pas les seules molécules impliquées dans la régulation de l'état hydrique (Yelenosky et Guy, 1989). La proline, la glycinebétaïne ou les polyols sont également des osmorégulateurs dont la synthèse est augmentée en période d'acclimatation au froid (Xin et Browse, 2000).…”

“…Le potentiel osmotique foliaire est une mesure plus globale qui permet de révéler des modifications de concentration en solutés intracellulaires en réponse aux basses températures (Guinchard et al, 1997). La mesure du potentiel osmotique réalisée après réhydratation de la plante permet de déterminer l'ajustement osmotique (accumulation active de solutés) réalisé par la plante en période d'acclimatation au froid (Yelenosky et Guy, 1989 (Campos et al, 2003 ;Janowiak et al, 2003), et également pour des tempéra-tures négatives (Nunes et Smith, 2003).…”