Plant Growth Regulation 21: 37–42, 1997. 37
c
1997 Kluwer Academic Publishers. Printed in the Netherlands.
A comparative study of the effects of abscisic acid and methyl jasmonate on
seedling growth of rice
Fei-Yi Tsai, Chuan Chi Lin & Ching Huei Kao
Department of Agronomy, National Taiwan University, Taipei, Taiwan, Republic of China (
author for correspondence)
Received 30 October 1996; accepted 4 November 1996
Key words: abscisic acid, grwoth, methyl jasmonate, Oryza sativa
Abstract
The effects of abscisic acid (ABA) and methyl jasmonate (MJ) on growth of rice seedlings were compared. The lowest tested concentration of ABA and MJ that inhibited seedling growth was found to be 4.5 and 0.9M,
respectively. Growth inhibition by ABA is reversible, whereas that by MJ is irreversible. GA3 was found to be
more effective in reversing inhibition of shoot growth by ABA than by MJ. KCl partially relieved MJ-inhibited, but not ABA-inhibited, growth of rice seedlings. The beneficial effect of K+
on growth of rice seedlings in MJ medium could not be replaced by Li+
, Na+
or Cs+
. MJ treatment caused a marked release of K+
into the medium. In order to understand whether cell wall-bound peroxidase activity was inversely related to rice seedling growth, effects of ABA and MJ on cell wall-bound peroxidase activity were also examined. Results indicated that both ABA and MJ increased cell wall-bound peroxidase activity in roots and shoots of rice seedlings. Although MJ (4.5M) was less
effective in inhibiting root growth than ABA (9M), MJ was found to increase more cell wall-bound peroxidase
activity in roots than ABA.
Abbreviations: ABA = abscisic acid; GA3= gibberellic acid; MJ = methyl jasmonate; POD = peroxidase
1. Introduction
Abscisic acid (ABA) is ubiquitous in higher plants and has many physiological effects on the growth and differentiation of plants [3]. It is usually accepted that ABA is a potent growth inhibitor, although in a few cases it may promote growth [1]. It has been shown that high levels of endogenous ABA maintains primaryroot growth and inhibits shoot growth of maize seedlings at low water potentials [11, 13]. Jasmonic acid and its methyl ester (MJ) have been proposed as naturally occurring plant growth regulators because of their wide natural distribution [10] and their effects on many physiological processes in plants [12]. Jasmonic acid or MJ inhibits seedling growth [16], stem growth [6] and callus growth [15]. In a recent work, Takahashi et al. [14] reported that jasmonic acid was effective in inducing expansion of potato cells and ABA markedly inhibited jasmonic acid-induced expansion of cells.
We have previously compared the effects of MJ and ABA on some rice physiological processes, such as induction of acid phosphatase in detached leaves, senescence of detached leaves, induction of callus from anthers, regeneration of callus derived from anthers, and 1-aminocyclopropane-1-carboxylic acid-dependent ethylene production in detached leaves [17]. In the present investigation, the effects of MJ and ABA on the growth of rice seedlings were extensively exam-ined and compared.
2. Materials and methods
Rice (Oryza sativa L., cv. Taichung Native 1) seeds were sterilized with 2.5% sodium hypochlorite for 15 min and washed thoroughly with distilled water. These seeds were then germinated in Petri dishes (20 cm) containing distilled water at 37
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Figure 1. Effects of ABA and MJ on seedling growth of rice. Seedling growth was measured after 5 days of treatment. Vertical bars represent
standard errors (n = 4). Only those standard errors larger than the symbols are shown.
1-day incubation, uniformly germinated seeds were selected and then transferred to Petri dishes (9.0 cm) containing two sheets of Whatman No. 1 filter paper moistened with 10 ml of distilled water or test solu-tions. Each Petri dish contained 20 germinated seeds and each treatment was replicated 4 times. The germi-nated seeds were grown at 27
C in darkness, and an additional 3 ml of distilled water or test solutions was added to each Petri dish on day 3 of the growth. Seedling growth (fresh weight) was measured after 5 days of treatment. Cell wall-bound POD was extracted according to the method described by Lee and Lin [7]. Cell wall-bound POD activity was measured using guaiacol as substrate [2]. One unit of cell wall-bound POD activity is defined as the amount of enzyme that caused the formation of 1mol tetraguaiacol per min.
All experiments described here were performed at least three times. Similar results and identical trends were obtained each time. The data reported here are from a single experiment.
3. Results and discussion
The effects of the concentrations of MJ or ABA on the growth of rice seedlings are presented in Figure 1. MJ markedly inhibited both root and shoot growth, as judged by fresh weight. Increasing MJ concentration
from 0.9 to 4.5M progressively inhibited seedling
growth. Growth of rice seedlings was also inhibited by ABA. However, the lowest tested concentration of ABA and MJ that significantly inhibited seedling growth was found to be 4.5 and 0.9M, respectively.
Ueda and Kato showed that MJ was more effective than ABA in inhibiting soybean callus growth [15].
The morphological changes of rice seedlings treated with ABA (9M) and MJ (4.5M) are shown
in Figure 2. If rice seedlings maintained for 3 days on ABA (9M) were transferred to distilled water they
then resumed both root and shoot growth (Figure 3). However, only slight growth of roots and shoots was observed if seedlings remained in ABA (Figure 3). These results indicate that the inhibition of seedling growth by ABA is reversible. In contrast, the inhibi-tion of seedling growth by MJ (4.5M) is irreversible,
because seedling growth could not be restored in MJ-treated seedlings if they were transferred to distilled water (Figure 3). It has been shown that ABA accu-mulate in leaves during water stress and ABA levels decline to prestress levels after rehydration [18]. The reversibility of ABA-inhibited seedling growth is most likely due to the decline of ABA levels in seedlings after they are transferred to distilled water. The irre-versibility of MJ-inhibited seedling growth implies that MJ is not readily metabolized in seedlings after they are transferred to distilled water. So far, not much is
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Figure 2. Effects of ABA and MJ on the morphology of rice seedlings. Rice seedlings were grown in water (left), 9M ABA (center) and 4.5 M MJ (right) for 5 days.
Figure 3. Changes in growth of ABA- or MJ-treated rice seedlings grown in the presence or absence of ABA (9M) or MJ (4.5M). One
day germinated rice seedlings were grown for 3 days in ABA (9M) or MJ (4.5M) and then seedlings were transferred to distilled water and
40
Figure 4. Effects of GA3applied together with ABA or MJ on the growth of rice seedlings. The concentrations of ABA and MJ were 9 and 4.5M, respectively. Seedling growth was measured after 5
days of treatment. Vertical bars represent standard errors (n = 4).
known about the metabolic pathways of jasmonates if exogenously applied. We do not know if metabo-lites of jasmonates exert activity in growth inhibition. However, this possibility can not be excluded.
Since the function of growth regulators is to coor-dinate the overall physiology of plants, interactions among them is essential to achieve balanced growth and development. ABA is known to interact with all the other plant growth regulators so far identified [19]. To characterize further the effects of ABA and MJ on the growth of rice seedlings, we conducted experi-ments to see if GA3(gibberellic acid) is able to reverse
the ABA- or MJ-mediated growth inhibition of rice shoots. Results are presented in Figures 4 and 5. GA3
was more effective in preventing the inhibition of shoot growth caused by ABA than that caused by MJ.
In a recent work, Aurisano et al. [1] demonstrated that KCl (10 mM) partially relieved the ABA-inhibited growth of root and shoot of wheat seedlings treat-ed with 100 M ABA. It has also been shown that
the rapid response to ABA involves an alteration in cell turgor which is driven by the movement of K+
and other anions [9]. Thus, it was of interest to know whether KCl interacted with ABA or MJ in inhibiting the growth of rice seedlings. MJ-inhibited growth of
Figure 5. Reversal of ABA- or MJ-inhibited shoot growth of rice
seedlings by GA3. One day germinated rice seedlings were grown for 3 days in distilled water, ABA (9M) or MJ (4.5M) and
then seedlings were transferred to the medium with or without GA3 (10M). Vertical bars represent standard errors (n = 4). Only those
standard errors larger than the symbols are shown.
rice seedlings (shoot and root) was partially reversed by KCl (Figure 6). However, KCl enhanced the ABA-mediated growth inhibition of rice seedlings (Figure 6). Additional experiments were conducted to see if other ions such as Li+
, Na+
or Cs+
could also reduce the growth inhibition caused by MJ. As indicated in Figure 6, neither Li+
, Na+
or Cs+
were able to reduce growth inhibition by MJ. It seemed that the process of MJ-inhibited seedling growth was accompanied by a reduced K+
level in seedlings or a release of K+
into the medium. To test this hypothesis, 3-day-old seedlings were treated with MJ (4.5M) for 24 h and
the K+
level in the medium was measured by flame photometry. It was found that MJ treatment caused a release of K+
into the medium of about 8.7mol
seedling 1 during the 24 h period, whereas about
3 nmol seedling 1was observed in its absence. It has been postulated by several investigators that the action of POD located in cell walls would be to confer rigidity to the cell wall and prevent expansion involved in growth [4, 5, 7, 8]. The present investiga-tion shows that cell wall-bound POD activity in shoots and roots was increased by ABA (9M) or MJ (4.5 M) treatment (Figure 7). MJ was less effective than
41
Figure 6. Effects of KCl, LiCl, NaCl and CsCl on ABA- or
MJ-inhibited growth of rice seedlings. The concentrations of ABA and MJ were 9 and 4.5M, respectively. Seedling growth was measured
after 5 days of treatment. Vertical bars represent standard errors (n = 4).
ABA in inhibiting both root and shoot growth (Figure 2). However, MJ was more effective in increasing cell wall-bound POD activity in roots than ABA (Figure 7). It is obvious that the role of cell wall-bound POD on ABA-inhibited root growth cannot be considered in terms of total activity alone.
Figure 7. Effects of ABA and MJ on cell wall-bound POD activity
in rice seedlings. The concentrations of ABA and MJ were 9 and 4.5M, respectively. The standard growth system was used and
cell wall-bound POD activity was assayed after 5 days of treatment. Vertical bars represent standard errors (n = 4).
Acknowledgements
This work was supported by the National Science Council of the Republic of China (NSC 85-2321-B002-091).
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