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The Effect of the Direction of Gravity on the Leaf Angle in Wheat (Triticum Aestivum)
Kurze Mitteilungen' Short Communications
Laboratoire d'Ecologie Vegerale, Universite de Louvain, Louvain-la-Neuve, Belgium
The Effect of the Direction of Gravity on the Leaf Angle in Wheat (Triticum Aestivum)
J. F. LEDENT With 2 figures Received May 2, 1980' Accepted May 23, 1980
Summary Wheat seedlings were grown upside down or on a vertical wheel rotating slowly. Leaf angle in the first leaves changed considerably with time independently of the direction of gravity. Differences from the controls were mostly due to elastic deformation. Leaf angle changes appeared to be basically of a nastic nature. Key words: leaf angle, geotropism nastles, wheat.
In wheat (Triticum aestivum 1.) all leaf laminae are vertical before their complete emergence out of the preceding sheath (or coleoptile, in the case of first leaf): leaf angle to the vertically held pseudostem is zero. As the leaves mature they change their orientation due to a downward rotation about their point of attachment to the sheath, the angle measured at the base increasing. The increase varies with genotype (LEDENT, 1978 a) and is influenced by environmental conditions such as temperature and photoperiod (LEDENT and Moss, 1977). It is also affected by leaf leverage and, in the case of uppermost leaves, by ear removal (LEDENT, 1978 b). However, the role played by gravity in these developmental changes has not previously been investigated. Two series of experiments have been conducted. In the first case plants were grown on a rotating wheel hence were subjected to a constantly changing gravity vector. In the second case plants were grown in an inverted position. The effect of these treatments on leaf angle was recorded. All experiments were conducted in growth chambers held at constant temperature (20 °e). Photoperiod was 16 h, and photosynthetic photon flux density was 20 n E cm-2sec-1 • Winter wheat c.v. Aaron was used in all experiments. This cultivar was known from previous work to display considerable changes in leaf angle with time (LEDENT, 1978). Z. Pflanzenphysiol. Bd. 100. S. 61-64. 1980.
62
].F.LEDENT
Th e norm al grav itational forces acti ng on th e plant were disturbed in two ways: Rotating plants. To change cont inually the dir ection of gravit y (relativ e to the plant axis), plants were grown on a slowly rotatin g verti cal wheel. Th e wh eel was dri ven by water at a rat e of about 0.4 revolutions/ minute. The wheel had a diameter of 63 em and 13 plastic containers, orient ed radially, were attached on the periphery. In each container two paper pot s (diameter 1.7 em, length 6.5) were att ached with clips. Paper pot s contained one seedling and wer e filled with a soil mixture. Seeds, which had been imbibed in pape r towel, were placed in th e cont ainers on the rot atin g wheel. Tr ansplantat ion to paper pot s too k place when coleoptiles were about 1 em long. Pl ant s were regularl y supplied with a mod ified H oagland solution. Inverted plants. The unid irectional act ion of gravi ty on the plant was eff ect ively reversed, tre ated plant s being grow n upside down as soon as the tip of the first leaf lamina became visible. To hold the plant axis vertically in treated plant s, a small count erweight (rubber sto ppe r, 2 g) was pinned at th e tip of the last expa ndin g lamina . This pr evented pseudostem cur vat ure due to a negati ve geotropism. Counterweights were removed and placed on the next expa nding leaf as soon as th e lamina was near ligule emergence. Leaf angle changes occurred only after ligule emergence, hence the counter weights could not directly affect them. Each plant s was in a 200 ml container fill ed with soil. Containers with tr eated plants were placed upside down on a wire netting above the controls. There were altogether 20 containers. Leaf angles were measured with a protr actor, the angle being taken as the angle between the basal part of the leaf mid rib and the pseudo stem (fig. 1). The leafy top of the plant (whateve r its orientation in space: normal or upside down ) was taken as indica ting the 00 direct ion, and the basis (roots) as indicating the 1800 direction. Measurements were ma de on th e first, second and th ird leaves to appear and they were taken at 1 or 2 days intervals.
As reported previously, the leaf angle of wheat leaves chan ges as the leaf matures (Fig. 2, open symbols) and plants grown on a slowly rotating wheel show similar, if less dram atic, changes (Fig. 2, circles). The effect is highly significant with time an d changing the gravity vector cont inuously did not prevent angle changes. Th e chan ge in leaf angle in invert ed plants (Fig. 2) was much decreased relative to norm al plants however the increase in leaf angle was not abolished, despite the fact that the lamin a had to rot at e agai nst the force of gravity . It was known that
z.
Pjlanzenphysiol. Bd. 100. S. 61-64. 1980.
Leaf angle and gravity in wheat
63
120
90
60
II
30
t::.
0
Fig. 2: Mean leaf angles. (a) first leaves of plants growing on a slowly rotating vertical wheel (e) (b) first and third leaves of plants growing upside down (~ and. respectively) and of controls C\l and 0). Least square deviations (p = 0.05) are indicated by vertical lines.
Table 1: Effect of plant orientation on angle') of lamina reduced Treatment
to
basal stumps.
Leaf First leaf
Second leaf
Third leaf
Control
90
68~
62
Plant growing upside down
57/
~(l4"":')
(21 NS) /' 80
~(23 NS)
/" 64
') Leaf angles to the vertical (tip of shoot: 0°)23 days after sowing, at 20°C; lamina reduced to stumps at the end of experiment. 1) Number between parentheses are LSD (p < 0.05) for pair of means indicated by the arrows; d. f. = 18. ".". signif. at p = 0.01: NS not signif. at p = 0.05.
leaf angle depended partly on reversible, elastic deformations due to leverage (LEDENT, 1978 b) and to eliminate this effect of leverage, lamina were cut off at the end of the experiment and the angle of the remaining basal stumps (2 em) measured. The mean leaf angles of tnt stumps for normal and inverted plants respectively are given in table 1. The effect of inversion was statistically significant only for the first leaf. Except for elastic deformation in the zone of attachment, the leaf angle changes seemed largely independent of gravity. Z. Pflanzenphysiol. Bd. 100. S. 61-64. 1980.
64
J. F.LEDENT
The increase in leaf angle with age in wheat plants occurs in normal plants, in inverted plants and in plants grown with a constantly changing gravitational vector. Although both types of treatment obviously placed plants under some stress, the developmental pattern was not greatly changed especially if one took into account elastic deformations.
Acknowledgement The author is thankful to R. D. FIRN and R. B. AUSTIN for help with the manuscript.
References LEDENT, J. F.: Changes in the angle and curvature of the uppermost leaves of winter wheat. Journal of Agricultural Science 90,319-323 (1978 a). - Mechanisms determining leaf movement and leaf angle in wheat (Triticum aestiuurn L.). Annals of Botany 42,345-351 (1978 b). LEDENT, ]. F. and D. N. Moss: Spatial orientation of wheat leaves. Crop Science 17, 873879 (1977).
JEAN-FRANS:OIS LEDENT, Laboratoire d'Ecologie Vegetale, 4 Place Croix du Sud, B-1348 Louvain-la-Neuve, Belgique.
Z. Pflanzenphysiol. Bd. 100. S. 61-64. 1980.
Laboratoire d'Ecologie Vegerale, Universite de Louvain, Louvain-la-Neuve, Belgium
The Effect of the Direction of Gravity on the Leaf Angle in Wheat (Triticum Aestivum)
J. F. LEDENT With 2 figures Received May 2, 1980' Accepted May 23, 1980
Summary Wheat seedlings were grown upside down or on a vertical wheel rotating slowly. Leaf angle in the first leaves changed considerably with time independently of the direction of gravity. Differences from the controls were mostly due to elastic deformation. Leaf angle changes appeared to be basically of a nastic nature. Key words: leaf angle, geotropism nastles, wheat.
In wheat (Triticum aestivum 1.) all leaf laminae are vertical before their complete emergence out of the preceding sheath (or coleoptile, in the case of first leaf): leaf angle to the vertically held pseudostem is zero. As the leaves mature they change their orientation due to a downward rotation about their point of attachment to the sheath, the angle measured at the base increasing. The increase varies with genotype (LEDENT, 1978 a) and is influenced by environmental conditions such as temperature and photoperiod (LEDENT and Moss, 1977). It is also affected by leaf leverage and, in the case of uppermost leaves, by ear removal (LEDENT, 1978 b). However, the role played by gravity in these developmental changes has not previously been investigated. Two series of experiments have been conducted. In the first case plants were grown on a rotating wheel hence were subjected to a constantly changing gravity vector. In the second case plants were grown in an inverted position. The effect of these treatments on leaf angle was recorded. All experiments were conducted in growth chambers held at constant temperature (20 °e). Photoperiod was 16 h, and photosynthetic photon flux density was 20 n E cm-2sec-1 • Winter wheat c.v. Aaron was used in all experiments. This cultivar was known from previous work to display considerable changes in leaf angle with time (LEDENT, 1978). Z. Pflanzenphysiol. Bd. 100. S. 61-64. 1980.
62
].F.LEDENT
Th e norm al grav itational forces acti ng on th e plant were disturbed in two ways: Rotating plants. To change cont inually the dir ection of gravit y (relativ e to the plant axis), plants were grown on a slowly rotatin g verti cal wheel. Th e wh eel was dri ven by water at a rat e of about 0.4 revolutions/ minute. The wheel had a diameter of 63 em and 13 plastic containers, orient ed radially, were attached on the periphery. In each container two paper pot s (diameter 1.7 em, length 6.5) were att ached with clips. Paper pot s contained one seedling and wer e filled with a soil mixture. Seeds, which had been imbibed in pape r towel, were placed in th e cont ainers on the rot atin g wheel. Tr ansplantat ion to paper pot s too k place when coleoptiles were about 1 em long. Pl ant s were regularl y supplied with a mod ified H oagland solution. Inverted plants. The unid irectional act ion of gravi ty on the plant was eff ect ively reversed, tre ated plant s being grow n upside down as soon as the tip of the first leaf lamina became visible. To hold the plant axis vertically in treated plant s, a small count erweight (rubber sto ppe r, 2 g) was pinned at th e tip of the last expa ndin g lamina . This pr evented pseudostem cur vat ure due to a negati ve geotropism. Counterweights were removed and placed on the next expa nding leaf as soon as th e lamina was near ligule emergence. Leaf angle changes occurred only after ligule emergence, hence the counter weights could not directly affect them. Each plant s was in a 200 ml container fill ed with soil. Containers with tr eated plants were placed upside down on a wire netting above the controls. There were altogether 20 containers. Leaf angles were measured with a protr actor, the angle being taken as the angle between the basal part of the leaf mid rib and the pseudo stem (fig. 1). The leafy top of the plant (whateve r its orientation in space: normal or upside down ) was taken as indica ting the 00 direct ion, and the basis (roots) as indicating the 1800 direction. Measurements were ma de on th e first, second and th ird leaves to appear and they were taken at 1 or 2 days intervals.
As reported previously, the leaf angle of wheat leaves chan ges as the leaf matures (Fig. 2, open symbols) and plants grown on a slowly rotating wheel show similar, if less dram atic, changes (Fig. 2, circles). The effect is highly significant with time an d changing the gravity vector cont inuously did not prevent angle changes. Th e chan ge in leaf angle in invert ed plants (Fig. 2) was much decreased relative to norm al plants however the increase in leaf angle was not abolished, despite the fact that the lamin a had to rot at e agai nst the force of gravity . It was known that
z.
Pjlanzenphysiol. Bd. 100. S. 61-64. 1980.
Leaf angle and gravity in wheat
63
120
90
60
II
30
t::.
0
Fig. 2: Mean leaf angles. (a) first leaves of plants growing on a slowly rotating vertical wheel (e) (b) first and third leaves of plants growing upside down (~ and. respectively) and of controls C\l and 0). Least square deviations (p = 0.05) are indicated by vertical lines.
Table 1: Effect of plant orientation on angle') of lamina reduced Treatment
to
basal stumps.
Leaf First leaf
Second leaf
Third leaf
Control
90
68~
62
Plant growing upside down
57/
~(l4"":')
(21 NS) /' 80
~(23 NS)
/" 64
') Leaf angles to the vertical (tip of shoot: 0°)23 days after sowing, at 20°C; lamina reduced to stumps at the end of experiment. 1) Number between parentheses are LSD (p < 0.05) for pair of means indicated by the arrows; d. f. = 18. ".". signif. at p = 0.01: NS not signif. at p = 0.05.
leaf angle depended partly on reversible, elastic deformations due to leverage (LEDENT, 1978 b) and to eliminate this effect of leverage, lamina were cut off at the end of the experiment and the angle of the remaining basal stumps (2 em) measured. The mean leaf angles of tnt stumps for normal and inverted plants respectively are given in table 1. The effect of inversion was statistically significant only for the first leaf. Except for elastic deformation in the zone of attachment, the leaf angle changes seemed largely independent of gravity. Z. Pflanzenphysiol. Bd. 100. S. 61-64. 1980.
64
J. F.LEDENT
The increase in leaf angle with age in wheat plants occurs in normal plants, in inverted plants and in plants grown with a constantly changing gravitational vector. Although both types of treatment obviously placed plants under some stress, the developmental pattern was not greatly changed especially if one took into account elastic deformations.
Acknowledgement The author is thankful to R. D. FIRN and R. B. AUSTIN for help with the manuscript.
References LEDENT, J. F.: Changes in the angle and curvature of the uppermost leaves of winter wheat. Journal of Agricultural Science 90,319-323 (1978 a). - Mechanisms determining leaf movement and leaf angle in wheat (Triticum aestiuurn L.). Annals of Botany 42,345-351 (1978 b). LEDENT, ]. F. and D. N. Moss: Spatial orientation of wheat leaves. Crop Science 17, 873879 (1977).
JEAN-FRANS:OIS LEDENT, Laboratoire d'Ecologie Vegetale, 4 Place Croix du Sud, B-1348 Louvain-la-Neuve, Belgique.
Z. Pflanzenphysiol. Bd. 100. S. 61-64. 1980.