Salt sensitivity of rice, maize, sugar beet, and cotton during germination and early vegetative growth
Abstract
Salinity is a common problem for agricultural productivity in many parts of the world and in land areas that have become arid.
A stage in the plant life-cycle vulnerable to salinity stress is
seed germination. Successful seedling establishment depends on
the frequency and the amount of precipitation as well as on the
ability of seed species to germinate and grow while soil
moisture and osmotic potentials decrease. The changes induced
by salinity in any one of the particular physiological or
anatomical parameters vary considerably. This depends on plant
species, stage of development, and external factors such as salt
regime. Based on this information, it is clear that the demands
for the use of salinized land for agricultural purposes and the
reinstatement of these lands for agricultural use in the present
time and in the future require a better understanding of the
nature of salt resistance and salt sensitivity during seed
germination. The present study was, therefore, conducted to
deal with the following objectives: Major objectives:
1. To determine the effect of different levels of
salinity (NaCl) on the germination of seeds (of sugar
beet, cotton, maize, and rice). 2. To investigate the extent of osmotic and specific ion
effects on germination by using different types of
inorganic salts: NaCl, CaCl2, and Na2SO4 on the abovementioned plant species.
3. To evaluate the effect of water potential (drought
simulation) using osmotic substances such as PEG and mannitol and comparing these with NaCl during germination on these plant species. Secondary objectives: I. Identify salt-resistance and salt-sensitive plants
during germination. II. To assess the exogenous application of GA3 and kinetinon germination and early seedlings growth under saltstress conditions. III. To identify differences in salt resistance among
species during germination and to identify the mechanisms that are responsible for these differences.
The results of the series of experiments are summarized as follows: a. Rice and maize showed high salt resistance during
germination. The data also indicates that germination
of cotton and sugar beet was more sensitive to the
stress caused by NaCl. b. When substrates of equal osmotic potentials are
applied, the overall effect of salts on germination
and early seedling growth appears to be as follows: Na2SO4 reduces germination much more than CaCl2 followed by NaCl. Any ranking of specific ions seems
to be difficult, since particular combinations of cations and anions appear to be more inhibitory thanothers. c. The results indicated, that isotonic solutions of PEG,
Mannitol and NaCl yielded similar germination percent and “root/shoot” length, indicating that the decrease in germination and other growth parameters may be due
primarily to an osmotic effect. d. Gibberellic acid and kinetin were found to be effective in alleviating salt-induced stress conditions in maize and sugar beet seeds. Particularly at the high level of salinity treatments, the effect of GA3 was greater than that of kinetin in
maize. However, the case was opposite in sugar beet. In general, seeds may be prevented from germination due to an inhibition of growth regulators or interference of salinity with metabolic activity. e. The presence of salt in the cells may induce changes in protein activity due to effects of ions on the structure of hydrating water which surrounds theprotein molecule. NaCl may also be inhibitory to the activities of some enzymes that play critical roles in seed germination. The poor germination and higher salt sensitivity of sugar beet (or cotton) may be linked to this and the following sugar input. This implies that transformation into soluble sugar is affected by the imposed stress.
