280
H. WALTER AND E. STADELMANN
The osmotic potential decreased from —10.7 to —21.6 atm. For the controls in the standard nutrient solution (—0.7 atm), the osmotic potential
remained at —10.9 atm. The rate of photosynthesis was not altered. Plants
transferred into the mannitol solution remained wilted. Their ψ 8 values,
however, also decreased to —21.0 atm, but this decrease was caused by
water loss. No increase in dry weight (indicative of photosynthetic activity) occurred.
Effects similar to those obtained with NaCl solutions were found also
with plants grown in KN0 3 solutions, although the increase in dry weight
was higher than in the controls, since KN0 3 may act as a nutrient. In
sucrose solutions, the uptake of sucrose was slower than that of the
electrolytes (Slatyer, 1961, pp. 524 and 525, Figs. 1 and 2).
Salt tolerance of the protoplasm of glycophytes used in this type of experiment is an important factor in survival. When Vicia faba plants were
transferred from a pure Knop solution to a Knop solution containing NaCl
(in a concentration corresponding to a decrease of osmotic potential
of —7.5 atm of the solution), the osmotic potential of the leaves reached
its final value twice as fast as in those plants transferred to Knop solutions
plus dextrans with the same osmotic potential. However, when the adapted
plants are transferred again into pure Knop solution, the plants of the dextran experiment showed no damage, whereas plants of the NaCl experiment were damaged. This indicated that protoplasm of Vicia faba was not
salt tolerant and NaCl at the concentration applied caused disturbances
of protein synthesis (Lapina, 1967, p. 321/273; 326/276).
After transfer of Phaseolus vulgaris plants from a nutrient solution into
a nutrient solution with added salt, the water stress triggered an osmoregulatory mechanism of additional ion uptake (initially K ions) into the
vacuole which adjusted the cell sap relatively quickly to the increased
concentration of the external solution [within 1 day for an increment of
\p s = — 1 atm (Bernstein, 1963); for effects of the magnitude of the daily
concentration increase on Hedysarum carnosum, see Hamza, 1969].
A similar reaction is found for seed germination in salt solutions. The
sum of the matric potential (capillarity, imbibition, hygroscopicity) and
of the osmotic potential resulting from salt content of the soil solution
gives total soil moisture stress. For the rate of germination of seeds only
the matric potential of the soil is of importance, while the osmotic potential
is compensated by salt uptake of the seeds. This was demonstrated in germination experiments with seeds of Medicago saliva and caryopses from
Avena sativa and Lolium perenne placed on sintered-glass plates which
were in contact with water (Collis-George and Sands, 1962, p. 581ff).
By increasing the water level difference in the experiment, the matric potential component of the water stress was increased and seed germination
H. WALTER AND E. STADELMANN
The osmotic potential decreased from —10.7 to —21.6 atm. For the controls in the standard nutrient solution (—0.7 atm), the osmotic potential
remained at —10.9 atm. The rate of photosynthesis was not altered. Plants
transferred into the mannitol solution remained wilted. Their ψ 8 values,
however, also decreased to —21.0 atm, but this decrease was caused by
water loss. No increase in dry weight (indicative of photosynthetic activity) occurred.
Effects similar to those obtained with NaCl solutions were found also
with plants grown in KN0 3 solutions, although the increase in dry weight
was higher than in the controls, since KN0 3 may act as a nutrient. In
sucrose solutions, the uptake of sucrose was slower than that of the
electrolytes (Slatyer, 1961, pp. 524 and 525, Figs. 1 and 2).
Salt tolerance of the protoplasm of glycophytes used in this type of experiment is an important factor in survival. When Vicia faba plants were
transferred from a pure Knop solution to a Knop solution containing NaCl
(in a concentration corresponding to a decrease of osmotic potential
of —7.5 atm of the solution), the osmotic potential of the leaves reached
its final value twice as fast as in those plants transferred to Knop solutions
plus dextrans with the same osmotic potential. However, when the adapted
plants are transferred again into pure Knop solution, the plants of the dextran experiment showed no damage, whereas plants of the NaCl experiment were damaged. This indicated that protoplasm of Vicia faba was not
salt tolerant and NaCl at the concentration applied caused disturbances
of protein synthesis (Lapina, 1967, p. 321/273; 326/276).
After transfer of Phaseolus vulgaris plants from a nutrient solution into
a nutrient solution with added salt, the water stress triggered an osmoregulatory mechanism of additional ion uptake (initially K ions) into the
vacuole which adjusted the cell sap relatively quickly to the increased
concentration of the external solution [within 1 day for an increment of
\p s = — 1 atm (Bernstein, 1963); for effects of the magnitude of the daily
concentration increase on Hedysarum carnosum, see Hamza, 1969].
A similar reaction is found for seed germination in salt solutions. The
sum of the matric potential (capillarity, imbibition, hygroscopicity) and
of the osmotic potential resulting from salt content of the soil solution
gives total soil moisture stress. For the rate of germination of seeds only
the matric potential of the soil is of importance, while the osmotic potential
is compensated by salt uptake of the seeds. This was demonstrated in germination experiments with seeds of Medicago saliva and caryopses from
Avena sativa and Lolium perenne placed on sintered-glass plates which
were in contact with water (Collis-George and Sands, 1962, p. 581ff).
By increasing the water level difference in the experiment, the matric potential component of the water stress was increased and seed germination