Preplant Physiological Seed Conditioning

Germination is an important stage in the life cycle of species growing in saline environments because it determines the soil conditions later stages in the life cycle will be exposed to. Laboratory investigations of seed germination indicate that seeds of most halophytic species reach their maximum germination in distilled water (Seneca, 1969; Onnis and Bellettato, 1972; Breen et al. 1977; Okusanya, 1977; Ungar, 1977a, 1978a; Zid and Boukhris, 1977; Dietert and Shontz, 1978). Seed germination in saline environments ordinarily occurs during the spring or in a season with high precipitation, when soil salinity levels are usually reduced (Ward, 1967; Chapman, 1974; McMahon and Ungar, 1978). Several studies have shown that seeds of many halophytes remain dormant when exposed to low water potentials (Ungar, 1962, 1974a, b, 1975, 1978a; Williams and Ungar, 1972).

Germination ecology of halophytes

Abiotic stresses can directly or indirectly affect the physiological status of an organism by altering its metabolism, growth, and development. The leaf growth and Chlorophyll content has significantly shown to vary from the control ones while the grain yield was not affected. While many plant species naturally accumulate proline and protein as major organic osmolytes when subjected to different abiotic stresses. These compounds are thought to play adaptive roles in mediating osmotic adjustment and protecting sub cellular structures in stressed plants. Different approaches have been contemplated to increase the concentrations of proline like compounds in plants grown under stress conditions to increase their stress tolerance. Seven different traditional rice varieties of Assam were evaluated for their response to osmolyte production under physiological drought condition through simulation at three levels of osmotic stress of 0.15 bar, 0.25 bar and 0.56 bar of physiological drought initiated by polyethylene glycol (PEG 6000). Along with the evaluation for osmolyte response the different components of genotypic variation for six different drought-sustaining characters in the seven rice varieties were also substantiated. The results indicated that plant height and seed number have significant genotypic coefficient of variability (GCV) and heritability. Verities like Laodubi, Leserihali, Beriabhanga and Borah were screened out as the best drought sustaining variety.

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Water Stress Effects on Leaf Growth and Chlorophyll Content but Not the Grain Yield in Traditional Rice ( Oryza sativa Linn.) Genotypes of Assam, India II. Protein and Proline Status in Seedlings under PEG Induced Water Stress

One: Biology and Biogeography of Halophytic Species and Salinity Controlled Ecosystems.- Wet halophytic ecosystems.- 1. Ecology of the halophytic vegetation of Egypt.- 2. Estuarine ecosystem of India.- 3. The biogeography of mangroves.- Dry halophytic ecosystems.- 4. Survey and adaptive biology of halophytes in western Rajasthan, India.- 5. Biology of Atriplex.- Two: Ecological and Ecophysiological Problems.- 1. Mangrove species zonation: why?.- 2. Distribution and environmental control of productivity and growth form of Spartina alterniflora (Loisel.).- 3. Germination ecology of halophytes.- 4. Aspects of salinity and water relations of Australian chenopods.- 5. Senescence in mangroves.- 6. Ecophysiological aspects of some tropical salt marsh halophytes.- 7. Adaptation of plants to saline environments: salt excretion and glandular structure.- 8. The role of bladders for salt removal in some Chenopodiaceae (mainly Atriplex species).- Three: Potentialities and Uses of Halophytic Species and Ecosystems.- 1. Halophytes and human welfare.- Plant index.

Contributions to the ecology of halophytes.

An experiment was conducted to see the impact of osmotic stress as it is one of the main cause in various soil and water disorders in agricultural field crops, speciallythe seed germination and seedling growth. The osmotic stress was generated using PEG-6000 and the seed germination, seedling growth were evaluated including the status of pigments i.e. chlorophyll (a, b and total), total carotenoids, pheophytin (a, b and total) and different enzymes like amylase, peroxidase, catalase and superoxide dismutase. The various osmotic potentials generated (-2, -5 and -10 bars) showed significant decrease in germination percentage as at the osmotic potential of -10 bars it was observed 70 in comparison to 90% of control. All the seedling growth parameter also showed inhibition with increase in osmotic potential. Increase in osmotic stress decreased Chlorophyll 'a', while Chlorophyll 'b' was increased in -5 bars while total chlorophyll showed decrease in -5 bars osmotic potential. Total carotenoids and pheophytin (a, b and total) were highly increased in -5 bars and decreased in -10 bars osmotic concentration. Enzymatic activity was found to be decreased in amylase while peroixidase, catalase and SOD were increased at different osmotic gradients in comparison to control. The data observed in the experiment can be helpful to assess the impact of any kind of osmotic stress on plant growth and development in crops.

Impact of osmotic stress on seed germination and seedling growth in black gram (Phaseolus mungo).

Water uptake patterns and germination rates of chickpea (Cicer arietinum L.) and vetch (Vicia faba L.), as affected by constant and changing external water potential, were studied experimentally. The initial water uptake rate was found to decrease as the external water poten tial decreased, due to reduced diffusivity to water of the seed coats, but the final water gained by imbibition was sufficient to ensure full germination. Germination rate decreased with a decrease in the external water potential. The data presented suggest that more work should be directed toward a better understanding of the effects of external water potential changes on the enzymatic activity during and after the imbibition stage.

A. Hadas

Papers

Water Uptake and Germination of Leguniinous Seeds Under Changing External Water Potential in Osmotic Solutions