The mechanic state of "inner tissue" in the growing zone of sunflower hypocotyls and the regulation of its growth rate following excision.

Spontaneous growth of isolated inner tissue from the etiolated sunflower (Helianthus annuus L.) hypocotyl growing zone was investigated. A new preparation technique allowed measurements starting 3 s after excision. Elongation with respect to the turgescent and plasmolized state was quantified in terms of relative growth rates, facilitating comparison to growth in situ. Turgor and turgor-induced strain were determined. Overall longitudinal strain in inner tissues in situ was positive, indicating that compressive forces exerted by peripheral tissues are outweighed by turgor-dependent tensile stress. Inner tissue expansion following isolation depended on water uptake. Extreme plastic extension rates occurred immediately after excision, suggesting that mechanical parameters of inner tissue in situ cannot be extrapolated from the mechanics of excised sections. In the long term, excised inner tissue autonomously established values of turgor, turgor-induced strain, and relative growth rates similar to values in the living plant. These results support historic models of tissue cooperation during organ growth, in which inner tissues actively participate in the control of growth rates.

[1]  Zygmunt Hejnowicz,et al.  Graviresponses in herbs and trees: a major role for the redistribution of tissue and growth stresses , 1997, Planta.

[2]  D J Cosgrove,et al.  Wall extensibility: its nature, measurement and relationship to plant cell growth. , 1993, The New phytologist.

[3]  N. Bernstein,et al.  The Determination of Relative Elemental Growth Rate Profiles from Segmental Growth Rates (A Methodological Evaluation) , 1997, Plant physiology.

[4]  Peters,et al.  The Correlation of Profiles of Surface pH and Elongation Growth in Maize Roots. , 1999, Plant physiology.

[5]  A. D. Tomos,et al.  THE PRESSURE PROBE: A Versatile Tool in Plant Cell Physiology. , 1999, Annual review of plant physiology and plant molecular biology.

[6]  R. Hunt Plant Growth Curves: The Functional Approach to Plant Growth Analysis , 1983 .

[7]  U. Kutschera The Role of the Epidermis in the Control of Elongation Growth in Stems and Coleoptiles , 1992 .

[8]  R. O. Erickson Modeling of Plant Growth , 1976 .

[9]  R. Firn,et al.  The Role of the Peripheral Cell Layers in the Geotropic Curvature of Sunflower Hypocotyls: a New Model of Shoot Geotropism , 1977 .

[10]  J. Passioura The physical chemistry of the primary cell wall: implications for the control of expansion rate , 1994 .

[11]  L. Taiz,et al.  Plant Cell Expansion: Regulation of Cell Wall Mechanical Properties , 1984 .

[12]  Zygmunt Hejnowicz,et al.  Tissue stresses in organs of herbaceous plants III. Elastic properties of the tissues of sunflowers hypocotyl and origin of tissue stresses , 1996 .

[13]  A. D. Tomos,et al.  The Epidermis Still in Control , 1996 .

[14]  U. Zimmermann,et al.  Transpiration Induces Radial Turgor Pressure Gradients in Wheat and Maize Roots , 1993, Plant physiology.

[15]  A. D. Tomos,et al.  The biophysics of differential growth. , 1989, Environmental and experimental botany.

[16]  A. D. Tomos,et al.  The history of tissue tension. , 1996, Annals of botany.

[17]  W. Silk,et al.  Quantitative Descriptions of Development , 1984 .

[18]  J. Boyer Cell enlargement and growth-induced water potentials , 1988 .

[19]  Stephen C. Fry,et al.  Turgor and Cell Expansion: Beyond the Lockhart Equation , 1992 .

[20]  D. Cosgrove,et al.  Solutes in the free space of growing stem tissues. , 1983, Plant physiology.

[21]  A. Bennett,et al.  A Text-Book of Botany , 2010, Nature.

[22]  A. Sievers,et al.  Tissue stresses in organs of herbaceous plants. II: Determination in three dimensions in the hypocotyl of sunflower , 1995 .

[23]  A. B. Meshcheryakov,et al.  Gradients of turgor, osmotic pressure, and water potential in the cortex of the hypocotyl of growing ricinus seedlings : effects of the supply of water from the xylem and of solutes from the Phloem. , 1992, Plant physiology.

[24]  K. Niklas,et al.  Preferential states of longitudinal tension in the outer tissues of Taraxcum officinale (Asteraceae) peduncles. , 1998, American journal of botany.