Plant Science 159 2000 117 – 124
Cerium and lanthanum promote floral initiation and reproductive growth of Arabidopsis thaliana
Ya-Wen He, Chiang-Shiong Loh
Department of Biological Sciences, National Uni6ersity of Singapore,
14
Science Dri6e
4
, Singapore
117543
, Singapore Received 1 December 1999; received in revised form 2 June 2000; accepted 5 July 2000
Abstract
The effects of cerium and lanthanum on the vegetative growth, floral initiation and reproductive growth of Arabidopsis thaliana were studied. Addition of cerium nitrate 0.5 – 10 mM or lanthanum nitrate 0.5 – 50 mM to the culture medium significantly
increased the lengths of primary roots, but had no significant effects on the number of rosette leaves produced per plant, plant heights and dry weights during the vegetative growth stage 17 days after seed germination. The percentage of plants bolted was
significantly increased with the addition of 0.5 – 10.0 mM cerium nitrate or lanthanum nitrate. The combination of 0.5 mM cerium nitrate and 0.5 mM lanthanum nitrate was found to be most effective on the induction of floral initiation. The height, dry weight
and average number of flower numbers of 35-day-old plants growing in media containing cerium nitrate orand lanthanum nitrate 0.5 – 10.0 mM were found to be significantly higher than those in the control medium. The endogenous levels of cytokinins zeatin
riboside, dihydrozeatin riboside and isopentenyl adenosine and carbohydrates sucrose, glucose and fructose in leaf and root tissues of plants growing in the medium supplemented with 0.5 mM cerium nitrate and 0.5 mM lanthanum nitrate were not
significantly different from those of plants in the control medium. Application of 0.5 mM cerium nitrate and 0.5 mM lanthanum nitrate enhanced the effects of 10
− 6
M IPA on root growth, plant height and flowering. The role of cerium and lanthanum in promoting floral initiation and reproductive growth and the possibility of developing non-hormonal flowering promoting agents
are discussed. © 2000 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Arabidopsis thaliana; Cerium; Lanthanum; Cytokinin; Flowering www.elsevier.comlocateplantsci
1. Introduction
The rare earth elements REEs comprise a group of 15 trivalent metallic elements with similar
chemical properties. They normally occur as basic oxides and phosphate complexes in nature [1,2].
Since the introduction of ion exchange techniques, the separation of the rare earth elements from
their ores and from one another has become prac- tical and many new uses of REEs have been
developed [3]. The widespread industrial usage of REEs makes it imperative that more detailed in-
formation on the effects of REEs on biological systems be available.
The effects of REEs, especially lanthanum, in different animal tissues have been studied exten-
sively [1]. Most of the work carried out on REEs in animal systems was based on the use of REE
ion as a substitute or antagonist for Ca
2 +
to monitor the movement of calcium and water, and
to investigate the role of calcium in muscle and nerve activity [4].
The results from limited studies on the effect of REEs on plant growth are conflicting. Early re-
ports indicated that the REE were inhibitory to plant growth. For example, La
3 +
and Nd
3 +
were found to inhibit elongation of oat coleoptile sec-
Abbre6iations
:
BA, benzyladenine; Ce, Cerium; DHZR, dihy- drozeatin riboside; IPA, isopentenyl adenosine; La, Lanthanum; MS
medium Murashige and Skoog 1962 medium; Nd, Neodymium; REEs, rare earth elements; ZR, zeatin riboside.
Corresponding author. Tel.: + 65-874-2916; fax: + 65-779-5671. E-mail address
:
dbslohcsnus.edu.sg C.-S. Loh. 0168-945200 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 0 0 0 0 3 3 8 - 1
tions [5]. Colloidal lanthanum caused an almost complete inhibition of cell division and root elon-
gation in the root tips of barley plants [6]. La
3 +
had been shown to inhibit root elongation of wheat
[7,8]. More
recent reports,
however, demonstrated some positive effects of REEs on
plant growth. Diatloff et al. [9] reported that corn root growth increased significantly with the
applications of cerium 0.63 mM and lanthanum 0.63
m M.
Applications of
lanthanum and
cerium were also reported to increase spike pro- duction in wheat [10]. In pot trials, applications
of cerium sulphate up to 100 mgkg enhanced root and shoot growth of Phaseolus radiatus and
Brassica pekinensis [11].
Results from field trials were also inconsistent. The increase in crop yield reported by workers
from China ranged between 8 and 50, with the common response being of the order of 8 – 15
[12,13]. However, no response was found by spraying and seed dressing of a summer fodder
crop Brassica sp. with REEs in a field trial carried out in Australia cited in [4]. In view of
this, it is essential to study and elucidate the effects of REE on essential stages of growth and
development of a model plant species such as Arabidopsis thaliana. In this report, we investi-
gated the effects of cerium Ce and lanthanum La on vegetative and reproductive growth of A.
thaliana and correlated some of the responses to increased sensitivity of cell to plant growth regu-
lators.
2. Materials and methods
