Diagravitropism in bermudagrass (cynodon dactylon (L.) Pers.) as determined by a gravitropic and a geoepinastic phenomenon

Plant Science, 51 (1987) 187-191

187

Elsevier Scientific Publishers Ireland Ltd.

DIAGRAVITROPISM IN B E R M U D A G R A S S (CYNODON DACTYLON (L.) PERS.) AS D E T E R M I N E D BY A GRAVITROPIC A N D A GEOEPINASTIC PHENOMENON

JORGE G. WILLEMO~S a, JOS]~ BELTRANO b and EDGARDO R. MONTALDI a'b

aConsejo Nacional de Investigaciones Cientificas y Tdcnicas (CONICET) and bInstituto de Fisiologia Vegetal, Facultad de Agronomla, Universidad Nacional de La Plata, C.C. 31 1900 La Plata (Argentina) (Received December 15th, 1986) (Revision received April 30th, 1987) (Accepted May 4th, 1987)

The purpose of this study was to elucidate whether different or similar mechanisms are involved in the upward and downward curvatures which determine the diagravitropic growth of bermudagrass stolons. Bermudagrass stolons subjected to omnilateral stimulation showed a 17'~ dorsoconvex curvature (geoepinasty), but this curvature did not occur when stolons were placed in a vertical position for more than 20 h before being rotated on a clinostat. High sucrose concentrations inhibited the curvature significantly, and gibberellic acid treatment overcame this effect. When different hypogravity conditions (0.06-1.00 × g) were simulated, the direction of the curvature was in all cases opposed to the acceleration vector (negative gravitropism), and a linear correlation between simulated hypogravity and curvature was found.

Key words: diagravitropism; geoepinasty; stolon; hypogravity; sucrose; clinostat

Introduction The plagiotropism of stems has often been ascribed to be an equilibrium between negative gravitropism and an epinasty or a positive gravitropism [1,2]. The upward curvature of diagravitropic organs, such as rhizomes, runners and stolons, has been assigned as a negative gravitropic response [3 5]. But very little is known about the movement which induces the downward curvature. Studying the behaviour of Fragaria vesca and Ranunculus repens stolons, Zimmermann [6] called this movement positive geotropism. However, Kaldewey [1] described it as a geoepinasty, based on its particular characteristics. To explain the diagravitropic growth of Polygonatum spp. rhizomes, Clapham [3] suggested that the downward curvature was caused by light reaching the base of the aerial shoot. This hypothesis would explain why

some diagravitropic organs, such as Cynodon dactylon stolons, show a negative gravitropic response when they are severed from the parent plant. Furthermore, Montaldi [7] demonstrated that sucrose synthesized by the parent plant maintained the diagravitropic growth of C. dactylon stolons. It has dlso been shown that a downward curvature of stolons in nearly vertical position can be provoked when a high sucrose solution is provided [8,9]. It is worthwhile mentioning t h a t gibberellic acid induces an upward curvature of horizontally growing C. dactylon stolons. This effect was observed both when spraying the parent plant and when immersing the stolon tips in gibberellic acid solutions [7]. The purpose of this study was to elucidate whether different or similar mechanisms are involved in the upward and downward curvature of horizontally growing bermudagrass stolons.

0618-9452/87/$03.50 ¢.(~ 1987 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland

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Materials and m e t h o d s Plants of bermudagrass (C. dactylon (L.) Pers.) were vegetatively reproduced from a clone collected at La Plata, Argentina. Stolons were severed from the parent plant, rooted in a mixture of sand and soil [1:2], transplanted into 1-1 pots, and grown in a greenhouse (mean temper a t ur e 27°C, fluence rate 1000 pE • m 2 . S 1 (A4o(~700 nm) at noon, and a photoperiod of 12 h). Apical pieces of stolons (explants), 10 cm long, were excised from the plants, and their cut ends immersed in 8-ml flasks containing the solution to be tested t h ro ug h a tight rubber stopper. Explants prepared in such a manner were subjected to omnilateral stimulation by rotating them on a Model 150 Multipurpose Rotor (Scientific Industries Inc., Springfield, Mass.) (Fig. 1), at a speed of I rev/400 s so t ha t no influence by centrifugal force (equivalent to 2.5 x 1 0 ~x g) was exerted on them [10]. In some experiments, explants were placed in a vertical position for different periods of time before being rotated on the clinostat. In other experiments, explants

were subjected to unilateral stimulation using a variable speed rotor. In this case, the rotation speed determined a centrifugal force equivalent to 0.06-1.00 x g, and thus it was possible to apply different quantities of stimulus at will. Care was t aken to arrange the morphological upper or lower side of the stolon always in the same way with respect to the axis of rotation. Bermudagrass stolons are horizontally growing stems with morphological dorsiventrality, so to study their c u r v a t u r e it was considered: dorsoconvex c u r v a t u r e as that directed towards the lower side of the organ, and dorsoconcave c u r v a t u r e that towards the upper side of it. After 48 h of rotation, explants were taken out from the flasks and their deflection angles with respect to the horizontal line were measured with a protractor. Treatments were made with gibberellic acid and sucrose. The concentrations used were those t hat had proved to be effective in modifying stem growth direction in C. dactylon [7]. Experiments were carried out in a growth chamber at 2TC and in darkness. Tabulated values correspond to the average of eight replications for each t r e a t m e n t and the standard error of the mean, and the significance of the differences between them was analyzed by Tukey's test [11].

Results

Fig. I.

Clinostat used for horizontal rotation of explants.

Bermudagrass stolons subjected to omnilateral stimulation, showed a 1 7 dorsoconvex curvat ure (Table I). This movement towards the lower side of the stolon was similar in all cases, regardless of placing them with the lower or upper side towards the axis of rotation. This dorsoconvex c u r v a t u r e was continuous along the stolon, in contrast with the gravitropic one, which was only seen in the nodes (Fig. 1). However, this c u r v a t u r e did not occur when stolons were placed in vertical position for more then 20 h before being rotated on the clinostat (Table II). Gibberellic acid treatments did not lead to significantly different dorsoconvex curvatures with respect to tap water, but high sucrose con-

189 T a b l e I. C u r v a t u r e of C. dactylon s t o l o n s r o t a t e d 48 h on a h o r i z o n t a l clinostat ( a p p r o x 0 x g) at 27°C. ( A v e r a g e of eight r e p l i c a t i o n s for each t r e a t m e n t and the S.E.M.) Treatment

C u r v a t u r e (°)

Tap w a t e r

17 _+ 3.21 a*

Gibberellic acid 1.44 × 10 - 5 M 2.88x10 5M

21 _ 4.30 a 20+4.22a

S u c r o s e 0.03 M 0.12 M 0.21 M 0.30M

16 _+ 4.38 a 12 _ 0.91 a 0 +_ 0.00 b 0 + 0.00b

S u c r o s e 0.30 M ÷ gibberellic acid 1.44 x 10 5 M 2.88 x 1 0 - ~ M

14 +_ 2.05 a 22 + 4.12a

Gibberellic acid 2.88×10 5M+sucrose 0.03 M 0.12 M 0.21 M 0.30 M

15 + 23 + 19 _ 14 +

2.11 4.30 2.79 3.22

a a a a

* M e a n s followed by the same letter are n o t significantly different.

centrations (0.21 and 0.30 M) inhibited the curv a t u re significantly. Moreover, the effect of high sucrose supply was overcome by gibberellic acid (Table I). The direction of the c u r v a t u r e in stolons subjected to hypogravity conditions between 0.06 and 1.00 × g was opposed to the acceleration vector (negative gravitropism). Thus, curv a t u r e was always directed towards the axis of rotation, regardless of the position of the stolons on the clinostat (Table III). A linear response was found between simulated h y p o g r av ity condition and curvature, with a correlation coefficient of 0.94 when stolons were arranged with the lower side towards the axis of r o t a t i o n and 0.97 when they were arranged with the upper side towards the axis of rotation. Stolons subjected to a hypogravity condition lower th an 0.06 × g showed a dorsoconvex

Fig. 2. C u r v a t u r e r e s p o n s e s of C. dactylon stolons. A: D o r s o c o n v e x c u r v a t u r e (geoepinasty). B: D o r s o c o n c a v e c u r v a t u r e (gravitropism).

T a b l e I I . C u r v a t u r e of C. dactylon s t o l o n s placed in vertical position for different periods of time and t h e n r o t a t e d 48 h on a horizontal c l i n o s t a t at 2 7 C . ( A v e r a g e of eight replications for each t r e a t m e n t and the S.E.M.) Period in vertical position (h)

Curvature ()

0 15 18 20 24

16 + 1.92 a* 15 + 3.53 a 19 _ 2.59 a 4 _+_3.71 b 0 ±0.00b

* M e a n s followed by the same letter are not significantly different.

190

Table III. Curvature of C. dactylon stolons in tap water subjected to hypogravity conditions. (Average of eight replications for each treatment and the S.E.M.) Lw: Stolons placed with the lower side towards the axis of rotation. Up: Stolons placed with the upper side towards the axis of rotation. Curvature ('~) g-force Lw

Up

1.00 0.75 0.54 0.24 0.06

80 ± 2.50 80 _+1.72 73 _ 2.80 40 ± 5.22 35 _+5.57

76 ± 2.67 69 ± 3.20 41 __+2.90 35 ± 3.77 19 ± 3.56

Correlation coefficient

r = 0.94

r = 0.97

c u r v a t u r e t o w a r d s the lower side of the o r g a n , similar to t h a t observed with o m n i l a t e r a l stimu l a t i o n (approx. 0 x g).

Discussion The d o r s o c o n v e x c u r v a t u r e of d e t a c h e d b e r m u d a g r a s s stolons subjected to g r a v i t y c o m p e n s a t i o n by c l i n o s t a t t i n g was c a u s e d by the differential g r o w t h of nodes a n d internodes. H o w e v e r , the d o r s o c o n c a v e curvat u r e p r o v o k e d by u n i l a t e r a l s t i m u l a t i o n was due only to the differential g r o w t h of nodes (Fig. 1), as it has been n o t e d for g r a v i t r o p i c c u r v a t u r e s in this and o t h e r grasses [5,11]. Thus, the r e s p o n s i v e n e s s of the tissues to gravity force differed a l o n g the stem. It is logical to a s s u m e t h a t stolons c u t off from the p a r e n t p l a n t and i m m e d i a t e l y r o t a t e d in a c l i n o s t a t (approx. 0 x g) h a d the s e n s o r m e c h a n i s m in position to c o m m a n d an epinastic m o v e m e n t t o w a r d s the lower side of the organ, r e g a r d l e s s of the position they were placed on the clinostat. So t h e r e m u s t be a p h y s i o l o g i c a l d o r s i v e n t r a l i t y in C. dactylon stolons w h i c h induces the c u r v a t u r e t o w a r d s the lower side. This a s y m m e t r y is a residual effect of g r a v i t y u n d e r w e n t in the field, since the d o r s o c o n v e x c u r v a t u r e did not o c c u r w h e n

the explants r e m a i n e d in a v e r t i c a l position for 20 h or l o n g e r before being clinostated. In a c c o r d a n c e with K a l d e w e y ' s view [1] the m o v e m e n t observed in stolons c l i n o s t a t t e d imm e d i a t e l y after excision s h o u l d be n a m e d geoepinasty. H i g h sucrose c o n c e n t r a t i o n s inhibited the g e o e p i n a s t i c response, and gibberellic acid o v e r c a m e this effect, as found in g r a v i t r o p i c responses [7]. This fact indicates that g e o e p i n a s t y and g r a v i t r o p i s m are p h e n o m e n a t h a t m a y h a v e a similar s u b c e l l u l a r mechanism. The n e g a t i v e g r a v i t r o p i c c u r v a t u r e was always g r e a t e r in those stolons placed with the lower side t o w a r d s the axis of r o t a t i o n t h a n in those in the opposite position, b e c a u s e the m o v e m e n t was c a u s e d by the c o m b i n a t i o n of a n e g a t i v e g r a v i t r o p i s m plus geoepinasty. In c o n t r a s t , the response of stolons placed with the u p p e r side t o w a r d s the axis of r o t a t i o n was the result of a n e g a t i v e g r a v i t r o p i s m m i n u s the geoepinasty. The results p r e s e n t e d seem to i n d i c a t e t h a t d i a g r a v i t r o p i s m in C. dactylon stolons depends u p o n a g r a v i t r o p i c u p w a r d c u r v a t u r e and a d o w n w a r d epinasty. Likewise, this e p i n a s t y is also a g r a v i t y - d e t e r m i n e d movement.

Acknowledgement This r e s e a r c h was s u p p o r t e d by a g r a n t from the Consejo N a c i o n a l de I n v e s t i g a c i o n e s Cientlficas y T~cnicas ( C O N I C E T ) .

References 1 H. Kaldewey, in: W. Ruhland (Ed.), Encyclopedia of Plant Physiology, Vol. XVII/2, Springer-Verlag, 1962, pp. 200--221. 2 N.G. Ball, in: F.C, Steward (Ed.), Plant Physiology. A Treatise, Vol. V A, Academic Press, 1969, pp. lli~ 228. 3 A.R. Clapham and N.G. Ball, in: F.C. Steward (Ed.), Plant Physiology. A Treatise, Vol. V A, Academic Press, 1969, p. 194. 4 J.H. Palmer, New Phytol., 55 (1956) 346-355. 5 E.R. Montaldi, RIA-INTA,Biol. Prod. Veg., 4 (1967) 5568.

191 6 W. Zimmermann and H. Kaldewey in: W. Ruhland, (Ed.), Encyclopedia of Plant Physiology, Vol. XVII]2, Springer-Verlag, 1962, p. 252. 7 E.R. Montaldi, Experientia, 25 (1969) 91. 8 E.R. Montaldi, Experientia, 29 (1973) 1031. 9 J. Beltrano and E.R. Montaldi, Phyton, 44 (1984) 107.

10 P. Larsen, in: W. Ruhland (Ed.), Encyclopedia of Plant Physiology, Vol. XVII/2, Springer Verlag, 1962, pp. 3473. 11 J.W. Tukey and F. Pimentel Gomes, in: Hemisferio Sur (Ed.), Curso de Estadistica Experimental, 1978, pp. 20-22.