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The growth physics and water relations of red-light-induced germination in lettuce seeds (1979)

Carpita, Nicholas C. ; Nabors, Murray W. ; Ross, Cleon W. ; [et al.]

Springer

Planta 144 (1979), S. 225-233

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ISSN: 1432-2048

Keywords: Dormancy (seeds) ; Germination (seeds) ; Lactuca ; Osmotic potential ; Pressure potential ; Water relations in seed germination ; Phytochrome and seed germination

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Using lettuce (Lactuca sativa L., cv. Grand Rapids) embryos in osmotica, we have demonstrated that when the growth rates of the embryonic axes of seeds treated with red (R) or far-red (FR) light are equalized, the axes of R-treated seeds develop a 3.4-bar decrease in water potential (paper No. III). As axial growth begins, reserve protein and phytin decrease rapidly, concomitant with increases in reducing sugars, α-amino nitrogen, and inorganic and esterified soluble phosphates. However, no differences between the axes of R-and FR-treated seeds are found with respect to the changes in these compounds, indicating that these changes arise as a result of growth and are not under immediate phytochrome control. Little change in the total lipid content is found in either treatment. The axes of FR-treated seeds hydrolyze endogenous sucrose at a greater rate thant those of R-treated seeds. Axes of R-treated seeds accumulate K+ and Na+ to a greater extent than those of FR-treated seeds. When potassium salts are added to the incubation medium, R induces increased K+ uptake by the axis and greater medium acidification by the axis. Malate and other organic acids and acidic amino acids increase at equal rates in both treatments, indicating that inorganic anions may also be taken up to balance the ionic charges. The results are compatible with the assumption that changes in the osmotic and pressure potentials of the embryonic axes of R-treated seeds are the result of a phytochrome-stimulated proton pump which, in whole dormant seeds, would initiate water-potential changes allowing the embryos to overcome the mechanical restraint of the surrounding seed layers, resulting in germination.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00388763

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Electronic Resource

The growth physics and water relations of red-light-induced germination in lettuce seeds (1979)

Carpita, Nicholas C. ; Nabors, Murray W. ; Ross, Cleon W. ; [et al.]

Springer

Planta 144 (1979), S. 217-224

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Details

ISSN: 1432-2048

Keywords: Dormancy (seeds) ; Germination (seeds) ; Lactuca ; Osmotic potential ; Pressure potential ; Water relations in seed germination ; Phytochrome and seed germination

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Irradiation of Grand Rapids lettuce (Lactuca sativa L.) seeds with red light (R) results in an increase in the growth response in the embryonic axes which enables them to overcome the mechanical restriction of the endosperm or the osmotic restriction of an external solution. When the growth rates of axes from R-and far-red(FR)-treated seeds are equalized with polyethylene-glycol-4000 solutions, a water potential difference of 3.4 bars between the axes is obtained. Measurements of the osmotic potential indicate a 1.0–2.0-bar difference between the treatments, depending upon incubation time. Although the difference in water potential remained constant during the growth of the axes, the osmotic constituents of the axes of R-treated seeds were diluted to a greater extent than those of the axes of FR-treated seeds. The length-to-volume ratio of the growing axes of R-treated seeds increased at a greater rate than that of the axes of FR-treated seeds. These data indicate that changes in the cell-wall properties may account for the remainder of the observed water potential difference. We propose that the phytochrome-mediated growth increase in these embryonic axes is an integrated function of the cells: increased wall loosening may be inextricably linked to simultaneous increases in the osmotic constitutents. The driving force for growth may not involve solely a change in the osmotic potential or the pressure potential, with passive readjustment of the other parameter, but the activation of a cellular component that links changes in the wall properties with the accumulation of osmotic constituents.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00388762

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