Plant Science 148 1999 175 – 183
Glycine betaine accumulation and induction of cold tolerance in strawberry Fragaria X ananassa Duch. plants
C.B. Rajashekar
a,
, H. Zhou
a
, K.B. Marcum
b
, O. Prakash
c
a
Di6ision of Horticulture, Kansas State Uni6ersity, Manhattan, KS
66506
, USA
b
Department of Plant Science, Uni6ersity of Arizona, Tucson, AZ
85721
, USA
c
Department of Biochemistry, Kansas State Uni6ersity, Manhattan, KS
66506
, USA Received 1 March 1999; received in revised form 9 July 1999; accepted 12 July 1999
Abstract
Endogenous glycine betaine levels in the leaves of strawberry Fragaria X ananassa Duch. plants were determined during cold acclimation and in response to exogenous abscisic acid ABA application. Glycine betaine levels in the leaves increased nearly
two-fold after 4 weeks of cold acclimation treatment during which the cold tolerance of leaves increased from − 5.8 to − 17°C. Exogenous application of ABA 100 mM to plants triggered glycine betaine accumulation in unhardened plants. It also increased
cold tolerance of leaves in both unhardened and cold-hardened plants. Similar to ABA, exogenous glycine betaine was effective in inducing cold tolerance in unhardened and cold-hardening plants. Exogenous application of glycine betaine 2 mM to
unhardened plants increased the cold tolerance of leaves almost two-fold within 72 h of application. In addition, it improved freezing survival and regrowth in whole plants. The results suggest that glycine betaine is involved in inducing cold tolerance both
in response to exogenous ABA and during natural cold acclimation of strawberry plants. © 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Fragaria X ananassa; Strawberry; Cold tolerance; Cold hardiness; Cold acclimation; Glycine betaine; Abscisic acid www.elsevier.comlocateplantsci
1. Introduction
Glycine betaine is known to accumulate in a wide range of plants under environmental stress
conditions [1]. By far, most of the work on glycine betaine in plants is focused on its possible role in
relation to osmotic and water stress [1,2]. Both osmotic and drought stress can trigger significant
accumulation of glycine betaine in many plants. This in part has lead the researchers to propose
that the accumulation of such compatible solute in plants is an adaptive mechanism against these
stresses [1,3,4]. Glycine betaine is known to accu- mulate in the cytoplasm as an osmolyte and may
have a stabilizing and protective action on proteins, enzymes and membranes under unfavor-
able and stressful conditions [5 – 10]. In addition to its role in osmotic and drought
stress, glycine betaine appears to be involved in low temperature stress in plants as well. Glycine
betaine has been shown to enhance the growth of bacteria at chilling temperatures [11]. Further-
more, it has been shown to protect thylakoid membranes against low temperatures in spinach
[12] and membrane integrity during freezing in alfalfa [13]. Glycine betaine has been known to
accumulate during cold acclimation in rye, barley, and wheat [14 – 16]. Although there have been
some studies dealing with protective effects of glycine betaine against low temperatures, its role
in plant cold tolerance and cold acclimation pro- cesses is not clear.
Considerable attention has been devoted to elu- cidate the role of ABA in cold tolerance of plants.
ABA has been associated with the cold acclima-
Corresponding author. Tel.: + 1-785-532-1427; fax: + 1-785-532- 6949.
E-mail address
:
crajasheoz.oznet.ksu.edu C.B. Rajashekar 0168-945299 - see front matter © 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 9 9 0 0 1 3 6 - 3
tion process in a number of plant species [17,18] and, when exogenously applied, it has been shown
to induce cold tolerance of plant cell cultures [19 – 21] as well as whole plants [17,18,22]. In fact,
exogenously applied ABA is known to induce greater cold tolerance more readily than the accli-
mating low temperatures do [18,19,23].
In this study we attempt to characterize the role of glycine betaine in cold acclimation and in in-
duction of cold tolerance in strawberry plants.
2. Materials and methods
