G. Nissim Amzallag

ADAPTATION VERSUS PRE-EXISTING RESISTANCE: AN INTERGENOTYPE ANALYSIS OF THE RESPONSE OF SORGHUM BICOLOR TO SALINITY

ABSTRACT Developmental and physiological responses of 11 Sorghum bicolor (L.) Moench genotypes exposed for 3 weeks to a 150 mM NaCl-pretreatment were studied. Following the pretreatment, exposure to 300 mM NaCl resulted in a gradient of response between “adaptation to salinity” (increase in salinity tolerance) and “pre-existing resistance” (maintenance of original salinity tolerance). Level of adaptation of each genotype was quantified by determination of the mean relative growth rate of the shoot at 300 mM NaCl ( ). There was a positive correlation between and the following parameters during the process of adaptation: inhibition of growth, decrease of the shoot:root ratio, and shoot Na+ uptake. There were more pronounced physiological perturbations during adaptation than during the pre-existing resistance response to salinity. During the first 25 days of exposure to NaCl, inhibition of growth and shoot Na+ concentration were not correlated. The much lower value for the intergenotype coefficient of variat...

THE RESPONSE OF PLANTS TO SALINITY: FROM TURGOR ADJUSTMENTS TO GENOME MODIFICATION

ABSTRACT The parameters affected by salinity in salt-sensitive plants are reviewed. Turgor is the potential energy which powers extension growth, but is not a parameter which controls the growth process. Cell expansion is affected by phytohormones, and salinity modifies the phytohormonal balance of the plant; one of the major effects of salinity on growth results from a modification of the phytohormonal balance. Exposure to salt of certain plant genotypes, under appropriate conditions, results in an increase in salt resistance, which has been termed adaptation. The capacity to adapt is limited to a precise period of development. The process of adaptation is accelerated by abscisic acid and inhibited by cytokinin. It is a genetic character which is not a property of all genotypes. Adaptation is transmitted to the next generation, which suggests that it involves a modification of the genome. In plants, genome organization and expression are modified during development and under various types of environmenta...

INDUCED MODIFICATIONS IN REPRODUCTIVE TRAITS OF SALT-TREATED PLANTS OF SORGHUM BICOLOR

ABSTRACT Plants of Sorghum bicolor were grown hydroponically in a solution containing 150 mM NaCl, and the reproductive characters were analyzed at the end of the life cycle. A subpopulation was exposed to salinity on day 8 following germination (early-exposed plants), and another subpopulation was first exposed to salinity on day 21 following germination (late-exposed plants). Fertility and stem height, as determined per g shoot dry weight (DW), were similar for control and late-exposed plants. However, these parameters were largely modified in early-exposed plants. The population of late-exposed plants displayed an increase in phenotypic variability. However, the monomodal structure of the population remained similar to that of the population of control plants. In contrast, a large increase in diversity was observed in the population of early-exposed plants, and the frequency distribution of the reproductive characters appeared as plurimodal for this population. Early exposure to NaCl has been previousl...

INFLUENCE OF THE MODE OF SALINIZATION ON REPRODUCTIVE TRAITS OF FIELD-GROWN PROGENY IN SORGHUM BICOLOR

ABSTRACT The offspring of Sorghum bicolor (L.) Moench plants exposed to 150 mM NaCl eight or twenty-one days following germination were grown in field conditions, and were irrigated with non-saline water. As compared to the offspring of non-treated plants, the progeny of plants early-exposed to NaCl displayed an increase in shoot dry weight and stem height, but some of them showed a significant decrease in fertility. Similar changes were observed, but to a lesser extent, in the offspring of plants late-exposed to salinity. A similar increase in phenotypic variability was observed in populations of progeny from early-and late-treated plants. After verifying that the changes observed did not result from an artifactual selection, it was concluded that the NaCl treatment is able to influence characters expressed during the late development of the plant progeny. The nature of the induced change is discussed in relation to the plant response, adaptation or resistance, induced by the early or late exposure to sa...

Brassinosteroid: A modulator of the developmental window for salt-adaptation in Sorghum bicolor?

Leaf development of salt-treated Sorghum bicolor plants is influenced by treatment with 24-epibrassinolide (EBL), but only during a short period in development. This transient sensitivity coincides with a critical period of reorganization of regulations already identified in Sorghum, during which adaptation (through integration of effects of external perturbation in the new regulation network) is possible. By measuring the effect of EBL on leaf malformations during their unfolding in plants exposed to 150 mM NaCl, it is shown that treatments with brassinosteroids (BR) enable modification of initiation, duration, and intensity of this critical period of reorganization. A critical period is characterized by modification of cell sensitivity to informative substances. Accordingly, it is suggested that BR, at specific concentrations and time in development, may induce changes in cellular sensitivity to many growth regulators. The parallels in the effects of EBL and NaCl suggest that the transient inhibition in leaf elongation is not directly caused by the perturbation (addition of EBL or sublethal NaCl treatment). Rather, it results from interference between an exogenous perturbation and the structure of the regulation network.

Dual response to nutrients in Sorghum bicolor: The role of critical periods in expression of adaptive plasticity

The growth response of Sorghum bicolor was followed for 34 days for plants exposed to modified nutrient concentrations from day 8 (early-treated) and from day 12 (late-treated) following imbibition. In late-treated plants, the effect of nutrient starvation on growth rate increased with time. In contrast, the influence of nutrient starvation was not cumulative in early-treated plants, and the rate of growth was stabilized (with regard to plants growing in a standard medium) after about ten days of treatment. This suggests an adaptive adjustment of early-treated plants to low-nutrient concentration. Differences between early and late-treated plants suggest that expression of this adaptive response is possible only during a critical period in development, the same already identified for salt-adaptation in Sorghum. A similar relationship between shoot weight and blade length was observed for all the early-treated plants. This contrasts with the two relationships noticed for late-treated plants exposed to simi...