Growth rates of tissue-cultured piantlets were reduced
under too high concentrations of nutrients
too low concerrb'ations of nutrients ,
low temperature and high temperature. In all cases, sizes of the
growth-induced water potential were linearly correlated to
cell elongation rates of plantlets. Because
the tissue culture vessel is closed, the humidity in the vessel
is almost saturated, and thus, it can be considered that
evaporation and transpiration from plant tissues are negligible.
If so, the water status of the culture media is the only
possible water source, and growing cells are the sink for
water uptake for plants grown under tissue culture conditions.
The mature tissue and xylem should have had identical
water potential because neither transpiration nor growth
occurred in the mature tissue and thus there was no net
water exchange. Therefore, it can be safe to say that the
water potential of mature tissue was similar to that of the
water source under tissue culture conditions. The growth
inhibition under tissue culture conditions implies that cell
elongation was inhibited by incapability of water uptake by
cells regardless of stress conditions . It is
evident that rates of water uptake by elongating cells are
dependent on sizes of the growth-induced water potential.
Under severe water stress conditions caused by high
salinity or drought, plants stop growing completely and
accumulate solutes in cells in order to maintain the size of
cell volume and turgor against dehydration. This phenomenon
is known as osmotic adjustment. Osmotic adjustment
has been observed in stem leaves , root and fruits . In soma cases, changes in cell wall properties and
loss of turgor can be limiting factors of cell elongation.
When cell expansion is taking place, the cell wall must be
pushed outward, and thus, the presence of turgor in the cell
is essential for cell expansion to supply a force to push the
wall toward the outside. Although turgor in the cell is
required, the growth-effective turgot is relatively small (Ikeda
eta/. 1996, Nonami and Boyer 1990a).
When maize kernels were cultured under high concentrations
of sucrose and sorbitol in vivo while call division was
significantly inhibited , a decrease in turgot
did not decrease expansion growth. Because cell expansion
rates were sustained with significantly reduced turgor in
maize kemel cells under tissue culture conditions , it is apparent that cell expansion was regulated by factors other than the size of turgot in expanding calls in
maize kernel cells. Turgor was found to be not related with
growth in some other instances. Little relation between turgor and growth was found
in expanding grape leaves. In Phycomyces, increasing cell turgor often caused only transitory
changes in enlargement. Contribution
of turgor on growth was questioned in a study of cell
expansion of Chara corallina by Zhu and Boyer. The cell elongation rate was highly dependent on energy metabolism as it was shown by using inhibitors that rapidly abolished
growth without changing the size of turgor. In many cases, turgor may not be a growthlimiting
factor. Instead suggested that, above the turgor threshold, the rapid response to energy
inhibitors indicates a control by metabolic reactions causing
synthesis and/or extension of cell wall polymers. Because
materials for cell wall synthesis were found to he osmotic
solutes during osmotic adjustment in soybean seedlings
when they were subjected to low water potentials it seems to be natural to conclude that
turgor maintenance is related to osmotic adjustment by using
metabolites and materials for cell wall synthesis when plants
are subjected to environmental stress conditions.
Growth rates of tissue-cultured piantlets were reducedunder too high concentrations of nutrientstoo low concerrb'ations of nutrients ,low temperature and high temperature. In all cases, sizes of thegrowth-induced water potential were linearly correlated tocell elongation rates of plantlets. Becausethe tissue culture vessel is closed, the humidity in the vesselis almost saturated, and thus, it can be considered thatevaporation and transpiration from plant tissues are negligible.If so, the water status of the culture media is the onlypossible water source, and growing cells are the sink forwater uptake for plants grown under tissue culture conditions.The mature tissue and xylem should have had identicalwater potential because neither transpiration nor growthoccurred in the mature tissue and thus there was no netwater exchange. Therefore, it can be safe to say that thewater potential of mature tissue was similar to that of thewater source under tissue culture conditions. The growthinhibition under tissue culture conditions implies that cellelongation was inhibited by incapability of water uptake bycells regardless of stress conditions . It isevident that rates of water uptake by elongating cells aredependent on sizes of the growth-induced water potential.Under severe water stress conditions caused by highsalinity or drought, plants stop growing completely andaccumulate solutes in cells in order to maintain the size ofcell volume and turgor against dehydration. This phenomenonis known as osmotic adjustment. Osmotic adjustmenthas been observed in stem leaves , root and fruits . In soma cases, changes in cell wall properties andloss of turgor can be limiting factors of cell elongation.When cell expansion is taking place, the cell wall must bepushed outward, and thus, the presence of turgor in the cellis essential for cell expansion to supply a force to push thewall toward the outside. Although turgor in the cell isrequired, the growth-effective turgot is relatively small (Ikedaeta/. 1996, Nonami and Boyer 1990a).When maize kernels were cultured under high concentrationsof sucrose and sorbitol in vivo while call division wassignificantly inhibited , a decrease in turgotdid not decrease expansion growth. Because cell expansionrates were sustained with significantly reduced turgor inmaize kemel cells under tissue culture conditions , it is apparent that cell expansion was regulated by factors other than the size of turgot in expanding calls inmaize kernel cells. Turgor was found to be not related withgrowth in some other instances. Little relation between turgor and growth was foundin expanding grape leaves. In Phycomyces, increasing cell turgor often caused only transitorychanges in enlargement. Contributionof turgor on growth was questioned in a study of cellexpansion of Chara corallina by Zhu and Boyer. The cell elongation rate was highly dependent on energy metabolism as it was shown by using inhibitors that rapidly abolishedgrowth without changing the size of turgor. In many cases, turgor may not be a growthlimitingfactor. Instead suggested that, above the turgor threshold, the rapid response to energyinhibitors indicates a control by metabolic reactions causingsynthesis and/or extension of cell wall polymers. Becausematerials for cell wall synthesis were found to he osmoticsolutes during osmotic adjustment in soybean seedlingswhen they were subjected to low water potentials it seems to be natural to conclude thatturgor maintenance is related to osmotic adjustment by usingmetabolites and materials for cell wall synthesis when plantsare subjected to environmental stress conditions.
การแปล กรุณารอสักครู่..
