Physical Basis for Altered Stem Elongation Rates in Internode Length Mutants of Pisum

Abstract

Biophysical parameters related to gibberellin (GA)-dependent stem elongation were examined in dark-grown stem-length genotypes of Pisum sativum L. The rate of internode expansion in these genotypes is altered due to recessive mutations which affect either the endogenous levels of, or response to, GA. The GA deficient dwarf L181 (Is), two GA insensitive semierectoides dwarfs NGB5865 and NGB5862 (Ika and Ikb, respectively) and the 'slender' line L197 (la crc), which is tall regardless of GA content, were compared to the wild-type tall cultivar, Torsdag. Osmotic pressure, estimated by vapor pressure osmometry, and turgor pressure, measured directly with a pressure probe, did not correlate with the differences in growth rate among the genotypes. Mechanical wall properties of frozen-thawed tissue were measured using a constant force assay. GA deficiency resulted in increased wall stiffness judged both on the basis of plastic compliance and plastic extensibility normalized for equal stem circumference. Plastic compliance was not reduced in the GA insensitive dwarfs, though Ika reduced circumference-normalized plasticity. In contrast, in vivo wall relaxation, determined by the

How Do Plant Cell Walls Extend?

“…Relaxation behavior consonant with these theoretical expectations was found in the growing stems of pea mutants (dwarfs) that were deficient in GA biosynthesis or were unresponsive to applied GA (Behringer et al, 1990). Plants with wild-type (tall) growth showed fast and large relaxations, whereas dw&f lines exhibited slower and smaller total relaxations.…”

Altered expression of expansin modulates leaf growth and pedicel abscission inArabidopsis thaliana

“…Petiole cell walls (1 cm) from the seventh leaf of 29-day-old plants were assayed with a custom-made extensometer (21). Because petiole diameters differed in the sense and antisense lines, the extensometer load was adjusted to give equal stress (force per unit area) by normalizing to wall cross-sectional area (22). Petiole cell-wall cross-sectional area was estimated as dry weight per unit length, giving values of 0.134, 0.147, and 0.101 mg͞cm for the control, sense, and antisense lines, respectively.…”

Genetic Dissection of the Relative Roles of Auxin and Gibberellin in the Regulation of Stem Elongation in Intact Light-Grown Peas

“…This suggests that the GA-increased stem elongation potential may be additionally mediated by an enhancement of the auxin induction of cell elongation. Such a role of GA may be attributed to a spectrum of GA actions, including a facilitation of solute translocation to the elongating cells (Reid and Ross, 1993), an increase in the rate of wall relaxation and a reduction in the yield threshold (Cosgrove and SovonickDunford, 1989;Behringer et al, 1990a), and a decrease in wall stiffening by loosening the cross-linking between polymers (Potter and Fry, 1993). The pronounced effect of GA on cell elongation a n d stem growth i n le mutants m a y also be partly mediated by the enhancement of auxin biosynthesis (Law, 1987, and refs. therein; Law a n d Hamilton, 1989) and the subsequent action of this auxin.…”

“…1029 Dunford, 1989;Behringer et al, 1990a). However, the mechanism underlying these GA-associated responses has not been fully determined.…”