Leaf Growth Controls the Timing of Panicle Initiation in Sorghum bicolor
Keywords:
defoliation, flowering, leaf elongation, panicle initiationAbstract
Flowering is initiated in grasses when the developmental program at the shoot apical meristem switches from producing vegetative to reproductive structures. The switch occurs via endogenous controls and in response to cues from the environment. Day-length is a major factor controlling flowering time and it is commonly believed to generate a signal in the green leaves which is transferred to the shoot apical meristem. Whether the signal is the flowering hormonal complex ‘florigen’, an electrical signal, or a multi-factorial process involving phytohormones and sugars remains inadequately backed by research. Many genes are said to control the onset of flowering in plants but the physiological mechanisms that switch those genes on-and-off remain hidden. Recent evidence shows that small signaling molecules may be implicated in but again not necessarily causal to the flowering process.
In the monocotyledon Sorghum bicolor the elongation rates of leaf primordia and of unexposed leaves (those wholly within the whorl) slowed during the vegetative developmental phase during a defined period prior to the initiation of panicle structures. The response was the same in treatments where the timing of panicle initiation was varied by season, agronomy, photoperiod, cultivar or defoliation. Moreover, in all treatments, panicle initiation was coincident to the attainment of both a common architecture of the shoot apex and comparable slowing of the elongation rates of leaf primordia and unexposed leaves. During vegetative development the total length of unexposed leaves was strongly dependent on the area of green leaf. We hypothesize that growth-related processes that slowed the elongation rate of leaf primordia and unexposed leaves might also have triggered panicle initiation. In a hereditary sense, this effect would ensure that the plant had sufficient leaf area and vegetative biomass to grow seed, in the same trend that those similar ancestors had adequate plant architecture and thus reproduced and survived.
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References
Bernier, G. 1988. The control of floral evocation and morphogenesis. Ann. Rev. Plant Physiol. Plant Mol. Biol. 39: 175-219.
Butler, D.G., Gilmour, A.R., Cullis, B.R. 1999. SAMM: an S-PLUS module for mixed models using REML. Inter. S-PLUS Conf., 21-22 October, New Orleans, USA.
Evans, L.T. 1993. The physiology of flower induction - paradigms lost and paradigms regained. Aust. J. Plant Physiol. 20: 655-660.
Hammer, G.L., Vanderlip, R.L., Gibson, G., Wade, L.J., Henzell, R.G., Younger, D.R., Warren, J., Dale, A.B. 1989. Genotype by environment interactions in grain sorghum. II. Effects of photoperiod and temperature on ontogeny. Crop Sci. 29: 376-384.
Hopkinson, J.M., Ison, R.L. 1982. Investigations into ripeness to flower in tobacco. Field Crops Res. 5: 335-348.
Irish, E.E., Jegla, D. 1997. Regulation of extent of vegetative development of the maize shoot meristem. The Plant J. 11: 63-71.
Irish, E.E., Karlen. S. 1998. Restoration of juvenility in maize shoots by meristem culture. Inter. J. Plant Sc. 159: 695-701.
Jaeger, K.E., Graf, A., Wigge, P.A. 2006. The control of flowering in space and time. J. Exp. Bot. 57(13): 3415-3418.
Kaitaniemi, P., Room, P.M., Hanan, J.S. 1999. Architecture and morphogenesis of grain sorghum, Sorghum bicolor (L.) Moench. Field Crops Res. 61: 51-60.
Kirby, E.J.M. 1990. Co-ordination of leaf emergence and leaf and spikelet primordium initiation in wheat. Field Crops Res. 25: 253-264.
Lauri, P.E. 1992. Données sur le contexte vegetatif lié à la floraison chez le cerisier (Prunus avium). Can. J. Bot. 70: 1848-1859.
Levy, A., Dean, C. 1998. The transition to flowering. The Plant Cell 10: 1973-1989.
Machackova, I., Krekule, J. 2001. Sixty-five years of searching for the signals that trigger flowering. Russ. J. Plant Physiol. 49 (4): 451-459.
Moncur, M.W. 1981. ‘Floral initiation in field crops.’ (CSIRO Publishing: Melbourne).
Muchow, R.C., Carberry, P.S. 1990. Phenology and leaf area development in a tropical grain sorghum. Field Crops Res. 23: 221-237.
Ockerby, S.E. 2001. Leaves shed light on flowering. PhD Thesis. Central Queensland University.
Ockerby, S.E., Midmore, D.J, Yule, D.F. 2001. Timing and height of defoliation affect vegetative growth and floral development in grain sorghum. Aust. J. Agric. Res. 52: 801-808.
Patterson, H.D., Thompson, K. 1971. Recovery of interblock information where block sizes are unequal. Biometrika 58: 545-554.
Pouteau, S., Nicholls, D., Tooke, F., Coen, E., Battey, N. 1997. The induction and maintenance of flowering in Impatiens. Development 124: 3343-3351.
Quinby, J.R., Karper, R.E. 1945. The inheritance of three genes that influence time of floral initiation and maturity date in milo. Agron. J. 37: 916-936.
Sachs, T. 1999. ‘Node counting’: an internal control of balanced vegetative and reproductive development. Plant, Cell and Environ. 22: 757-766.
Simpson, G.G., Gendall, A.R., Dean, C. 1999. When to switch to flowering. Ann. Rev. Cell and Dev. Biol. 99: 519-550.
Sunderland, N. 1961. Cell division and expansion in the growth of the shoot apex. J. Exp. Bot. 12: 446-457.
Tooke, F., Battey, N.H. 2000. A leaf-derived signal is a quantitative determinant of floral form in Impatiens. The Plant Cell 12: 1837-1847.
Verbyla, A.P., Cullis, B.R., Kenward, M.G., Welham, S.J. 1997. The analysis of designed experiments and longitudinal data using smoothing splines (with discussion). App. Stat. 48: 269-311.
Williams, R.F. 1975. The shoot apex and leaf growth: a study in quantitative biology. Cambridge University Press, Cambridge, pp. 142-145.
Williams, R.F., Williams, C.N. 1968. Physiology of growth in the wheat plant. 4. Effects of daylength and light energy level. Aust. J. Biol. Sci. 21: 835-854.
Zeevaart, J. 1976. Physiology of flower formation. Ann. Rev. Plant Physiol. 27: 321-348.
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