Amzallag's Sorghum Studies

Protoplasma. 2006 May; 227 (2-4):113-8
Chromosome endoreduplication as a factor of salt adaptation in Sorghum bicolor.
M Ceccarelli, E Santantonio, F Marmottini, G N Amzallag, P G Cionini
Dipartimento di Biologia Cellulare e Ambientale, Università di Perugia, Perugia, cionini@unipg.it.
Nuclear DNA amounts were measured by Feulgen cytophotometry in Sorghum bicolor cv. 610 plants early exposed to 150 mM NaCl, a treatment known to induce an increased tolerance to salinity in plants carrying this genotype. In salt-treated plants, the percentages of 8C, 16C, and 32C nuclei in roots in the primary state of growth were 21.9%, 13.3%, and 4.3%, respectively. By contrast, in nonsalinized plants, only 3.5% of the nuclei had an 8C content and no higher DNA contents were observed. The salt treatment induced chromosome endoreduplication during the differentiation of cells in the root cortex, where 41.2% of the cells displayed a DNA content higher than 4C (versus 1.3% in control plants). No enhancement of endopolyploidy was observed in cells of the root vascular cylinder or the leaves of the salt-treated plants. In another S. bicolor genotype (DK 34-Alabama), noncompetent for salt adaptation, the same NaCl treatment did not induce chromosome endoreduplication in root cortex cells. Endopolyploidy may be considered as a part of the adaptive response of S. bicolor competent genotypes to salinity.

J Exp Bot. 2005 Nov; 56 (421):2821-9
Perturbed reproductive development in salt-treated Sorghum bicolor: a consequence of modifications in regulation networks?
G Nissim Amzallag
The Judea Center for Research and Development, Carmel, 90404, Israel. nissamz@bgumail.bgu.ac.il
In Sorghum bicolor, tolerance to salinity is improved by a 3-week treatment with 150 mM NaCl during early vegetative development. However, a strong decrease in fertility is also observed, suggesting that reproductive development becomes perturbed by this adaptive response to salinity. This study is an attempt to clarify the origin of such a paradoxical phenomenon. The relationships between end-cycle characters are modified by the NaCl treatment: some linkages disappear, while others are strengthened, especially those linking fertility with plant height. In parallel, a transient reduced level of linkage between leaf characters is observed around the unfolding of the eighth to the tenth leaves, defining a critical period in vegetative development separating two discrete phases. A relationship is observed between events occurring during this short critical period and the NaCl-induced perturbations in fertility. This suggests that reproductive development is conditioned by the influence of salinity on events occurring during a short period of vegetative development, independently of the level of tolerance to salinity quantified by the rate of vegetative growth.

J Theor Biol. 2004 Aug 7;229 (3):361-9
Adaptive changes in bacteria: a consequence of nonlinear transitions in chromosome topology?
G N Amzallag
The Judea Center for Research and Development, Carmel 90404, Israel. nissamz@bgumail.bgu.ac.il
Adaptive changes in bacteria are generally considered to result from random mutations selected by the environment. This interpretation is challenged by the non-randomness of genomic changes observed following ageing or starvation in bacterial colonies. A theory of adaptive targeting of sequences for enzymes involved in DNA transactions is proposed here. It is assumed that the sudden leakage of cAMP consecutive to starvation induces a rapid drop in the ATP/ADP ratio that inactivates the homeostasis in control of the level of DNA supercoiling. This phase change enables the emergence of local modifications in chromosome topology in relation to the missing metabolites, a first stage in expression of an adaptive status in which DNA transactions are induced. The nonlinear perspective proposed here is homologous to that already suggested for adaptation of pluricellular organisms during their development. In both cases, phases of robustness in regulation networks for genetic expression are interspaced by critical periods of breakdown of the homeostatic regulations during which, through isolation of nodes from a whole network, specific changes with adaptive value may locally occur.

Theory Biosci. 2004 Jun; 123 (1):17-32.
Critical periods as fundamental events in life.
G Nissim Amzallag
The Judea Center for Research and Development, 90404, Carmel, Israel, nissamz@bgumail.bgu.ac.il.
Development is not a continuous phenomenon. Rather, phenophases are interspaced with short critical periods. This phenomenon reflects an alternance between stabilization (during a phenophase) and dismantling (during a critical period) of a network of between-organ relationships generating the organism. Networks of relationships may be compared to dissipative systems in physics. In this context, a critical period represents a transient phase of isolation of the systems enabling its evolution towards equilibrium. As suggested here, this transition from dissipative to isolated system represents the source of newly emerging dissipative structures in which environmental or developmental perturbations are adaptively integrated. In contrast to non-living systems, an endogenous control of the transition towards critical period seems to exist during development. By extension to other scales of biological organization, it is suggested that the capacity to self-define its status (dissipative or close-to-equilibrium) represents the key property of living systems. This asks for a reconsideration of some basic notions about life, such as the role of genes in normal development, in physiological adaptation, and even in the emergence of evolutionary novelty.

Plant, Cell & Environment. 2001 Mar; 24 (3): 337–345.
Maturation of integrated functions during development. I. Modifications of the regulatory network during transition periods in Sorghum bicolor
G. N. Amzallag
Gibberellin (GA) and cytokinin (CK) were exogenously supplied at different periods of the vegetative development in Sorghum bicolor. Growth response to these hormonal treatments differed according to the developmental stage. This reveals the existence of discrete phenophases, each one characterized by a specific sensitivity to plant growth regulations (PGRs). Developmental changes in sensitivity were less accentuated in plants grown in optimal conditions than in plants exposed to 150 mm NaCl. Variations in organ connectance (the level of coordination in growth of the shoot, adventitious roots and seminal root) were analysed during vegetative growth of salt-treated plants. This analysis shows a temporary decrease in connectance during the transition period between phenophases. From the effect of hormonal treatments on connectance, it was concluded that (i) the transition period coincides with a partial dismantling of the initial regulatory network followed by the emergence of a new network coordinating growth of the different organs; (ii) GA is involved in the process of emergence of a transition period; and (iii) duration of the transition period is considerably enlarged for plants exposed to NaCl stress. This dynamics of alternance of phenophase and transition periods enables the integration of the two modes of action of the PGRs (dose–response and change in sensitivity) within a unified framework.

Biosystems. 2000 Jul; 57 (2):95-107.
Canalization as a non-genetic source of adaptiveness during morphogenesis: experimental evidence from analysis of reproductive development in Sorghum bicolor.
G N Amzallag
Department of Plant Sciences, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel.
In Sorghum bicolor, perturbations in reproductive development observed following salt-treatment also influence progeny grown in the absence of NaCl. However, a developmental reversion of these modifications may be observed throughout two successive generations. This response, termed canalization, does not spontaneously occur following growth in the absence of NaCl, but is triggered by the level of perturbation in parental expression of reproductive characters. Moreover, canalization is not specific to the perturbed character, but it includes modifications in reproductive development as a whole. A decrease in developmental variability coincides with amplitude of the developmental reversion. This phenomenon is interpreted as an evidence for orientation of the developmental process towards the lowest free-energy state of the 'epigenetic landscape'. Involvement of this phenomenon of canalization in developmental stability, adaptiveness, and evolution is discussed. Moreover, these results point to the need for a posteriori methods of investigations in order to analyze self-organized transformations in biological systems.

New Phytologist. 2000 Jun; 146 (3): 483-492.
Maternal Transmission of Adaptive Modifications in Salt-Treated Sorghum bicolor: A First Stage in Ecotypic Differentiation?
G. Nissim Amzallag
Following a 3-wk pretreatment with 150 mM NaCl, Sorghum plants were able to survive exposure to 300 mM NaCl, a lethal concentration for nonpretreated plants. This response is termed salt adaptation. Although the population was initially homogeneous, Na-includer and Na-excluder individuals coexisted after the achievement of the salt-adaptation response, and a large diversity in size of the seeds produced was observed at the end of the life cycle. Offspring of salt-adapted plants were exposed to a new salt-adaptation treatment. Even in the absence of selection, the proportion of Na-excluder individuals in the progeny was significantly increased. Offspring germinated from small seeds differed significantly from plants first-exposed to a salt-adaptation treatment, whereas offspring from large seeds displayed intermediate characteristics. This suggests that some of the adaptive changes were transmitted through embryo imprinting. The importance of this phenomenon for emergence of a newly adapted ecotype is discussed.

Biosystems. 2000 Mar; 56 (1):1-11.
Connectance in Sorghum development: beyond the genotype-phenotype duality.
G N Amzallag
Department of Plant Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
Connectance, the level of linkage between organs, was measured in different lines of Sorghum bicolor during their reproductive development. It was compared with expression of characters, their level of variability and their heritability. A negative relationship is observed between connectance and heritability. Further results indicate that connectance does not simply introduce a noise factor in expression of a pre-existing information, but that it is directly involved in phenotypic expression and plasticity. Connectance appears as partly determined by the nature and dynamics of the network of relationships. It is concluded that the phenotype is not restricted to the deterministic expression of a pre-existing program, the genotype. Morphogenesis also involves another dimension, self-organized, which confers reliability, stability and adaptability to the developmental processes. The complex interactions between these two dimensions and their evolutionary consequences are discussed.

Plant, Cell & Environment. 1999 Nov; 22 (11): 1389-1399.
Individuation in Sorghum bicolor: a self-organized process involved in physiological adaptation to salinity
G. N. Amzallag
In Sorghum bicolor, salt-adaptation was defined as the capacity of plants to grow at 300 m mol NaCl (a lethal concentration) following a 3-week pre-treatment with 150 m mol NaCl (a sublethal concentration). Large populations induced for salt-adaptation were analysed. Two modes of osmotic regulation (Na-includer and Na-excluder) were differentiated during induction of salt-adaptation, in spite of the genetic and environmental homogeneity. This variability was not related to any incapacity of the Na-includers to control accumulation of Na+ ions in the shoot, because most of the pre-treated plants displayed a similar capacity of growth and control of Na+ uptake after transfer to 300 m m NaCl. This unsuspected complexity of initially homogeneous populations points on the inadequacy of physiological studies focused on the ‘average individual’. Further analyses showed that variability was not directly related to micro-environmental variations. It is concluded that a process of individuation is caused by a third source of variability, which is the expression of a self-organizing process normally occurring during the transition phases in development. In constraining environments, this phenomenon of individuation includes adaptive modifications.

Plant, Cell & Environment. 1999 Aug; 22 (8): 1035-1041
Adaptive nature of the transition phases in development: the case of Sorghum bicolor
G. N. Amzallag
An increase in tolerance to salinity is induced in Sorghum bicolor by exposure to a sublethal concentration of NaCl during early vegetative development. The phase of competence for induction of this response, termed salt adaptation, is well defined in time and it coincides with the emergence of the first adventitious roots. The link between these events was investigated. Competence for salt adaptation varies among genotypes. It is shown that competence is especially high for genotypes in which the link between the seminal root and the shoot is reduced during emergence of the adventitious root. These data relate the capacity for salt adaptation with development in the absence of NaCl, suggesting that: (i) functional integration of the adventitious roots within the whole plant has an adaptive nature in normal development; (ii) salt adaptation results from an integration of the environmental constraint (NaCl) during this developmental readjustment. It is concluded that perturbations generated by emergence of a new organ are the cause of rapid variations in sensitivity required to open a competence window.

New Phytologist. 1996 Feb; 132 (2): 317-325
Transmissible Reproductive Changes Following Physiological Adaptation to Salinity in Sorghum bicolor
G. Nissim Amzallag
A 3 wk exposure to 150 mM NaCl induced adaptation to salinity in 8-d-old seedlings of Sorghum bicolor (L.) Moench. This treatment, defined as standard adaptation treatment, modified the expression of the reproductive traits, and the relationship between vegetative and reproductive organs. The adaptation response was accelerated when 8-d-old seedlings were sprayed daily with abscisic acid (ABA) for 10 d. Adaptation was also enhanced when seedlings were exposed to salinity on day 5, instead of day 8, after germination. These adaptation treatments, applied during the early vegetative development, influenced the expression of late reproductive characters. Thus besides the direct disturbing effect of NaCl, the adaptation process also has a specific influence on the expression of the sexual characters. Offspring of adapted plants were exposed to a standard adaptation treatment. The expression of the reproductive traits of the progeny was generally less perturbed than in their parents, where treatment influenced characters such as fertility, plant height and seed size of the progeny. Therefore, the adaptation process induced stable and transmissible changes in the expression of the reproductive characters. An analogy between changes induced by salt adaptation in Sorghum plants and somaclonal variations is suggested. The evolutionary significance of the adaptation response is discussed.

Biosystems. 1995; 36 (1):71-7
Adaptive determinism during salt-adaptation in Sorghum bicolor.
H Seligmann, G N Amzallag
Department of Botany, Hebrew University, Jerusalem, Israel.
During adaptation to salinity, plants of Sorghum bicolor showed malformations affecting the leaves in development (DPL). At the end of the adaptation process, the plants were regrouped according to their pattern of DPL response. The distribution of the plant population in different patterns depended on environmental conditions. However, a positive relationship between the frequency of a pattern and its rate of development has been found. Similarly, a negative relation between the frequency of a pattern and the rate of senescence for the same pattern has been observed. The results reveal the existence of an orientation of the plant response towards the patterns with highest developmental rate and lowest rate of senescence. This property is defined as 'adaptive determinism'. Results indicate that the NaCl acts as a trigger for adaptation to a whole range of environmental perturbations. This suggests that adaptation to salinity is not a pre-programed response of the plants, and may be related to learning processes occurring in animals.

J. Exp. Bot. 1995; 46 (8): 1017-1024.
Induced variability during the process of adaptation in Sorghum bicolor
G. N. Amzallag, H. Seligmann and H. R. Lerner
Department of Botany, The Hebrew University of Jerusalem 91904 Jerusalem, Israel
The coefficient of variation of some anatomical and physiological parameters has been measured in plants of Sorghum bicolor (L.) Moench exposed to conditions inducing adaptation to salt. The kinetic analysis of the variability of shoot DW and shoot Na+ concentration revealed a specific phase of increase in variability between days 6 and 16 following exposure to salinity. The increase in variability observed in a population of adapted plants, as compared to a population of control plants, appeared as a whole plant process since variability for most of the parameters were positively correlated. Variability within plant populations of 11 Sorghum genotypes, each presenting a different capacity for adaptation, was determined during the middle of the adaptation process. A strong linkage between the level of adaptation and the increase in variability was observed. The relatively low level of variability observed in populations of Sorghum varieties which did not adapt to salinity suggested that the increase in variability was not a direct consequence of exposure to stress conditions, but that it was specifically related to the adaptation process. The data presented suggest the occurrence of modifications at the level of genome expression during the adaptation process.

New Phytologist. 1994 Dec; 128 (4): 715-723.
Influence of Parental NaCl Treatment on Salinity Tolerance of Offspring in Sorghum bicolor (L.) Moench
G. N. Amzallag
Adaptation and resistance responses to NaCl salinity have been expressed in Sorghum bicolor (L.) Moench (genotype MP610) by exposure to 150 mol m-3 NaCl respectively 8 or 21 d after germination. Offspring of the adapted or the resistant plants (respectively named A1 and R1) were compared with offspring of control plants (C1). Eighteen days after germination in presence or absence of 75 mol m-3 NaCl, the A1 plants showed a large increase in vigour, and a reduction in Na+ accumulation into the shoot, compared with the C1 plants. The R1 plants were widely heterogeneous and presented intermediate characteristics between the A1 and C1 plants. When first exposed to salinity 21 d after germination, the A1 plants showed a significant increase in salinity tolerance, when compared with C1 plants. Conversely, the R1 plants remained very similar to the C1 plants after late exposure to salinity. These results indicate that the exposure of Sorghum plants to salinity induced an increase in vigour in the progeny. Moreover, an enhanced salinity-tolerance is specifically observed for offspring of adapted plants, suggesting that this property is not a simple consequence of parents grown in a saline environment. The possible nature of the observed effects on offspring is discussed.

J. Exp. Bot. 1993; 44 (3): 645-652.
A Developmental Window for Salt-Adaptation in Sorghum bicolor
G. N. Amzallag, H. Seligmann and H. R. Lerner
Following exposure to specific NaCl treatments, certain Sorghum bicolor genotypes developed increased salinity tolerance, 'adaptation', which was accompanied by a morphological modification in the development of one or several leaves. Adaptation differed from the more common response of the plant to salinity, 'pre-existing resistance', which rested on the prevalent tolerance mechanisms existing prior to the salinization treatment. Induction of adaptation was possible only during a specific time period of plant development. This time-limited capacity for adjustment to a changing environmental parameter, developmental window, resembled similar processes occurring in animal development.

Australian Journal of Plant Physiology. 1993; 20 (2) 243-249.
Perturbed Leaf Development in Sorghum bicolor Exposed to Salinity: a Marker of Transition Towards Adaptation
H Seligmann, GN Amzallag and HR Lerner
Pretreatment for 3 weeks with NaCl, within the range 35-150 mol m-3, of 8 day old Sorghum bicolor cv. 610, results in adaptation of the plants to high salinity; plants become tolerant to 300 mol m-3 NaCl, which is lethal for unadapted plants. During the adaptation period one or more developmentally perturbed leaves (DPL) may occur. DPL formation is positively correlated with the mean relative growth rate (RGR) of the plant following exposure to 300 mol m-3 NaCl, which reflects the degree of adaptation to high salinity. Treatments with exogenous phytohormones affect both DPL formation as well as the adaptation response. When plants 14 days old or more are exposed to salinity, neither adaptation nor DPL formation occurs, demonstrating the existence of a developmental window during which these phenomena may take place. These data suggest that DPL does not result from salt damage to the plant, but rather that it should be considered as a marker of the adaptation process.