Salinity continues to be one of the world’s most serious environmental problems in agriculture. The increasing world population and urbanization are forcing farmers to utilize marginal lands as well as poor quality water. One of the strategies in dealing with salinity is growing salt tolerant plants and there has been increased need to understand the effects of salinity on crops. Owing to its high nutritive value and wide adaptability to diverse environments, amaranth is considered a promising crop for marginal lands and semiarid regions. The objective of the study was to investigate the response of amaranth to salinity stress and evaluate stress amelioration by calcium and seed priming. Salinity tolerance during germination and early seedling growth was examined for six genotypes of amaranth (Amaranthus species) at different salt concentrations ranging from 0 to 200 mM NaCl or Na2SO4. Enhancement of germination was observed at 25 mM, while increasing salt concentrations reduced the germination percentage as well as germination rate. A.tricolor and Accession ’83 were able to germinate in 200 mM NaCl while there was no germination at 200 mM Na2SO4 in all the genotypes. Overall, Accession ’83 was the most resistant and A. hybridus the most sensitive genotype, particularly at high salt concentrations. Inhibition of germination was greater in Na2SO4 than in NaCl salinity treatments. Amaranth was more salt tolerant at germination than at seedling growth. Seedling emergence, survival and growth were reduced by salinity and at much lower concentrations than at seed germination. Differences in salt tolerance were noted among the genotypes. Salinity stress was initiated at different growth stages (cotyledon stage, 2-leaf stage and 4-leaf stage) in order to determine whether tolerance of amaranth differs with the stage of development. The treatment either continued until termination of the experiment or for 14 days at each stage. Amaranth plants were less sensitive to salinity when the stress was initiated at the 4-leaf stage. Lower salt concentrations had less detrimental effects than higher concentrations when applied at the cotyledon stage. Application of low salt concentration at cotyledon stage for 14 days did not have any effect on plant growth. The results indicate that it is feasible to use saline water for growing amaranth with minimum yield losses if salt concentration, duration of exposure and time of salinization are carefully managed. Differences in salinity tolerance among amaranth genotypes were analyzed in terms of plant survival, growth, gas exchange, water use and leaf anatomical changes. A. hypochondriacus and A. cruentus showed greater tolerance to salinity since they survived in 200 mM NaCl treatment and the reduction in growth at 50 and 100 mM was lower than that of A. tricolor and Accession ’83. A. hypochondriacus and A. cruentus were more efficient water users and partitioned photosynthates towards shoot growth as opposed to the other two genotypes. Photosynthetic rate, stomatal conductance, stomatal density and apertures were reduced by salinity but were higher in A. tricolor than in A. cruentus. Salinity resulted in A. cruentus developing thicker leaves compared to A. tricolor. Productivity on saline soils can be increased by growing genotypes more tolerant to salinity. The interactive effect of salinity and water stress on amaranth plant growth was evaluated. It was found that the reduction in shoot growth was greater in plants submitted to water stress than in those submitted to salt or salt + water stress. Water use efficiency was increased while leaf water and osmotic potentials were reduced by the salinity stress treatments. In drying soil plants previously salinized had a greater degree of osmotic adjustment, so that plants were able to continue growth for a longer period compared to water stressed plants. The effect of calcium in ameliorating salt stress was investigated. Supplementary calcium, either as CaSO4 or CaCl2 ameliorated the negative effects of salinity on growth, gas exchange, membrane permeability and mineral uptake. In a separate experiment it was shown that it is feasible to mitigate the adverse effects of salinity on amaranth seed germination, seedling survival and growth by seed priming and that the positive effect of priming persisted to vegetative growth stage. Priming with CaSO4 + NaCl showed a greater positive response than priming with the individual salts. / Thesis (PhD (Plant Production andSoil Science))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O presente trabalho teve por objetivo estudar as respostas fisiolÃgicas e bioquÃmicas de plÃntulas de cajueiro anÃo-precoce (Anacardium occidentale L.) à salinidade em duas condiÃÃes ambientais de cultivo. Para isso, as plÃntulas foram cultivadas em vasos de polietileno contendo somente soluÃÃo nutritiva (tratamento controle) ou soluÃÃo nutritiva com NaCl a 50, 100, 150 e 200 mM (tratamentos salinos), sendo mantidas em duas condiÃÃes ambientais: casa de vegetaÃÃo e sala de germinaÃÃo. Os efeitos do estresse salino foram avaliados atravÃs de medidas de crescimento, trocas gasosas, teores de clorofila, potencial osmÃtico foliar e teores de solutos orgÃnicos (prolina, N-aminossolÃveis e carboidratos solÃveis) e inorgÃnicos (Na+, Cl- e K+) nas folhas e raÃzes. TambÃm foram estudadas as alteraÃÃes na expressÃo gÃnica com a salinidade, o que foi feito atravÃs da comparaÃÃo dos padrÃes eletroforÃticos 2D das proteÃnas de folhas e raÃzes. A salinidade reduziu o crescimento das plÃntulas em ambas as condiÃÃes ambientais de cultivo, sendo que nas plÃntulas da casa de vegetaÃÃo, a inibiÃÃo do crescimento foi mais acentuada do que naquelas da sala de germinaÃÃo. Este fato correlacionou-se com as maiores reduÃÃes na fotossÃntese lÃquida, na transpiraÃÃo e na condutÃncia estomÃtica das plÃntulas da casa de vegetaÃÃo em relaÃÃo Ãs da sala de germinaÃÃo. Nas duas condiÃÃes de cultivo, os efeitos inibitÃrios do NaCl foram mais conspÃcuos nas raÃzes do que na parte aÃrea. A salinidade nÃo causou grandes mudanÃas nas concentraÃÃes internas de CO2 das plÃntulas de cajueiro, sugerindo a participaÃÃo de fatores nÃo-estomÃticos na inibiÃÃo das taxas fotossintÃticas. Os teores foliares de clorofila a, b e total foram influenciados pela salinidade e pelas condiÃÃes de cultivo das plÃntulas, sendo que as da sala de germinaÃÃo apresentaram os maiores conteÃdos e as menores reduÃÃes desses pigmentos devido à salinidade. As leituras feitas com o medidor portÃtil de clorofila, SPAD-502, correlacionaram-se positivamente com os teores foliares de clorofila, expressos em g.cm-2, tanto nas plÃntulas da casa de vegetaÃÃo quanto nas da sala de germinaÃÃo. As maiores reduÃÃes no potencial osmÃtico e os maiores acÃmulos de Na+ e Cl- nas folhas pela salinidade, em relaÃÃo ao controle, foram observados nas plÃntulas da casa de vegetaÃÃo. Por outro lado, os teores de K+ nesse ÃrgÃo nÃo diferiram muito entre as duas condiÃÃes de cultivo empregadas. As raÃzes acumularam grandes quantidades de Na+ e Cl- em seus tecidos, as quais foram acompanhadas de grandes decrÃscimos nos teores de K+, em ambas as condiÃÃes de cultivo. Com o aumento da salinidade, os teores de prolina foram aumentados, principalmente nas folhas, sendo os maiores incrementos observados nas plÃntulas da casa de vegetaÃÃo. Os teores de carboidratos solÃveis foram aumentados e reduzidos, devido à salinidade, somente nas folhas das plÃntulas da sala de germinaÃÃo e nas raÃzes das plÃntulas da casa de vegetaÃÃo, respectivamente. Nas duas condiÃÃes de cultivo, a salinidade aumentou os teores de N-aminossolÃveis nas folhas e nas raÃzes das plÃntulas de cajueiro. O padrÃo de expressÃo gÃnica das folhas e das raÃzes foi alterado pelo estresse salino em ambas as condiÃÃes ambientais. A salinidade causou aumentos e diminuiÃÃes nas taxas de expressÃo de vÃrias proteÃnas, sendo que algumas desapareceram completamente e outras foram aparentemente sintetizadas de novo nas plÃntulas estressadas. As proteÃnas diferencialmente reguladas pelo estresse salino foram bastante diferentes nas duas condiÃÃes ambientais empregadas. Faz-se necessÃrio o seqÃenciamento e a identificaÃÃo dessas proteÃnas para que se possa especular sobre seus possÃveis papÃis no processo de aclimataÃÃo das plÃntulas de cajueiro Ãs condiÃÃes de salinidade. / Early-dwarf cashew seedlings (Anacardium occidentale L.) were used in order to investigate the physiological and biochemical changes induced by salt stress in two environmental conditions. The seedlings were cultivated in plastics pots containing only nutrient solution (control treatment) or nutrient solution with NaCl at 50, 100, 150 and 200 mM (saline treatment). They were kept in two environmental conditions: greenhouse and growth room. The effects of salinity on the growth, gas exchange, chlorophyll content, osmotic potential and organic (proline, soluble amino-N, soluble carbohydrates) and inorganic (Na+, Cl-, K+) solute contents from both leaves and roots were studied. Salt stress induced changes in gene expression were studied both in leaves and roots comparing 2D electrophoretic pattern. Salinity inhibited the growth of seedlings in both environmental conditions, being the reduction in seedlings growth in the greenhouse more conspicuous than those cultivated in the growth room. This fact was correlated with highest reductions in net photosynthetic rate, in transpiration and stomatal conductance of seedlings grown in the greenhouse when compared with those of growth room. In both cultivation conditions, the root growth was affected by NaCl than shoot growth. The salinity stress not caused great changes in CO2 internal concentration, suggesting that the inhibition of photosynthesis also may be attributed to non-stomatal factors. Leaf chlorophyll a, b and total contents were influenced by salinity and environmental conditions, being observed the highest contents and the lowest reductions of these pigments due to salinity in seedlings under growth room conditions. The readings of portable chlorophyll meter, SPAD-502, were positively correlated to leaf chlorophyll contents, expressed in g.cm-2, both in greenhouse and growth room conditions. In the salt stress conditions, the higher reductions of osmotic potential and higher Na+ and Cl- accumulations in leaves were observed in seedlings grown in the greenhouse. On the other hand, leaves K+ contents did not differ much among the cultivation conditions used. The roots accumulated greater amounts of Na+ and Cl- in their tissues, which were accompanied of great decreases in the K+ contents in both cultivation conditions. Proline content increased with the increase in salt stress especially in leaves, being the greater increases observed in seedlings cultivated in the greenhouse. The soluble carbohydrates contents were increased and decreased, due to salinity, only in leaves of seedlings of growth room and roots of those grown in the greenhouse, respectively. In both cultivation conditions, salinity increased the leaf and root soluble amino-N contents of cashew seedlings. The gene expression patterns both leaves and roots were altered by salt stress, in both environmental conditions. Salinity induced increases and decreases in expression of various proteins, being that some proteins disappeared completely and other were apparently synthesized de novo in the seedlings stressed. The proteins differentially regulated by salt stress were enough different among the environmental conditions used. Future studies should be focused on sequencing and identification of proteins whose rate of synthesis varied as a result of salinity, in order to better characterize their possible roles in the process of acclimation of cashew seedlings to salinity conditions