Nostoc rivulare was grown in batch cultures under controlled CO2 and NO3 – concentrations to modulate the photosynthetic source:sink relationship. Increasing CO2 supply accelerated the accumulation of chlorophyll (Chl) a, i.e., supplemental CO2 combined with double concentrations of NO3 – more than doubled the amounts of Chl a relative to those of the original medium. Photosynthetic oxygen evolution and respiratory oxygen uptake were both enhanced by elevated CO2 and NO3 –. Contents of soluble sugars and starch (total non-structural saccharides) as well as insoluble saccharides (structural fraction) were affected by altering CO2-NO3 – combinations. Uptake as well as reduction of either NO3 – or NO2 – was inhibited by CO2 deprivation. Expanding the sink size via increasing NO3 – supply enhanced photosynthesis and thus the sink (NO3 –) acted as a feed forward stimulator of the source (photosynthesis). The regulatory role of nitrate on photosynthesis was most influential in CO2-deprived cultures since it could enhance photosynthesis to higher levels than CO2-supplemented, nitrate-free cultures.

Nostoc rivulare was grown in batch cultures under controlled CO2 and NO3 – concentrations to modulate the photosynthetic source:sink relationship. Increasing CO2 supply accelerated the accumulation of chlorophyll (Chl) a, i.e., supplemental CO2 combined with double concentrations of NO3 – more than doubled the amounts of Chl a relative to those of the original medium. Photosynthetic oxygen evolution and respiratory oxygen uptake were both enhanced by elevated CO2 and NO3 –. Contents of soluble sugars and starch (total non-structural saccharides) as well as insoluble saccharides (structural fraction) were affected by altering CO2-NO3 – combinations. Uptake as well as reduction of either NO3 – or NO2 – was inhibited by CO2 deprivation. Expanding the sink size via increasing NO3 – supply enhanced photosynthesis and thus the sink (NO3 –) acted as a feed forward stimulator of the source (photosynthesis). The regulatory role of nitrate on photosynthesis was most influential in CO2-deprived cultures since it could enhance photosynthesis to higher levels than CO2-supplemented, nitrate-free cultures.

Efficient de novo shoot organogenesis from hypocotyl and cotyledons was studied under NaCl-salinity conditions and in a salinity-calcium combination. Sodium chloride inhibited shoot regeneration markedly at 100 and 150 mM NaCl. Both the fresh and dry weight were also reduced. The mineral contents (Na, K and Ca) of hypocotyl and cotyledonary cultures were disturbed at high levels of NaCl salinity. The osmotic potential (Ř s) was raised in hypocotyl and cotyledonary cultures in MS medium as the NaCl salinity level increased. Calcium enhanced shoot regeneration in hypocotyls and cotyledonary cultures, especially at the highest salinity level (150 mM NaCl). This calcium-induced counteraction of the harmful effect of NaCl may be due to the reduced uptake of Na and to the elevated water content of hypocotyls and cotyledonary cultures under Na-Ca combination. wall rigidity.

Efficient de novo shoot organogenesis from hypocotyl and cotyledons was studied under NaCl-salinity conditions and in a salinity-calcium combination. Sodium chloride inhibited shoot regeneration markedly at 100 and 150 mM NaCl. Both the fresh and dry weight were also reduced. The mineral contents (Na, K and Ca) of hypocotyl and cotyledonary cultures were disturbed at high levels of NaCl salinity. The osmotic potential (Ř s) was raised in hypocotyl and cotyledonary cultures in MS medium as the NaCl salinity level increased. Calcium enhanced shoot regeneration in hypocotyls and cotyledonary cultures, especially at the highest salinity level (150 mM NaCl). This calcium-induced counteraction of the harmful effect of NaCl may be due to the reduced uptake of Na and to the elevated water content of hypocotyls and cotyledonary cultures under Na-Ca combination. wall rigidity.

Efficient de novo shoot organogenesis from hypocotyl and cotyledons was studied under NaCl-salinity conditions and in a salinity-calcium combination. Sodium chloride inhibited shoot regeneration markedly at 100 and 150 mM NaCl. Both the fresh and dry weight were also reduced. The mineral contents (Na, K and Ca) of hypocotyl and cotyledonary cultures were disturbed at high levels of NaCl salinity. The osmotic potential (Ř s) was raised in hypocotyl and cotyledonary cultures in MS medium as the NaCl salinity level increased. Calcium enhanced shoot regeneration in hypocotyls and cotyledonary cultures, especially at the highest salinity level (150 mM NaCl). This calcium-induced counteraction of the harmful effect of NaCl may be due to the reduced uptake of Na and to the elevated water content of hypocotyls and cotyledonary cultures under Na-Ca combination. wall rigidity.

The effect of salicylic acid (SA: 0.5 mM) on the plant growth, copper accumulation, Cu-bound proteins and protein pattern in roots and shoots of Helianthus annuus plants under Cu stress (5 mg L-1) was studied. Cu stress reduced the fresh and dry weights of sunflower plants. Cu markedly accumulated in Cu-stressed plants. However, this accumulation of Cu was higher in roots than in shoots. Chromatography of cell free extract of Cu-binding proteins of cu-stressed plants revealed three main protein peaks in roots and four peaks in leaves. The main peak for copper is coincident with protein of molecular weight of 75 kDa and contains about 89.40 and 80.84% of the total copper in the soluble fraction in roots and leaves, respectively. Proteins pattern shows that, Cu-stress induced the synthesis of new polypeptides of 178 and 97 kDa in plant roots and 105, 81 kDa in case of plant leaves. SA increased the fresh and dry weights of Cu-stressed plants. SA lowered the Cu content both in the roots and shoots of Cu-stressed plants. This was associated an increase in the endogenous SA content in the two organs. Cu plus SA treatment revealed 4 protein peaks with molecular weights about 175, 130, 75 and 35 kDa in roots and 175, 130, 100 and 45 kDa in case of leaves. The main peak for copper is coincident with protein of molecular weight 75 kDa in roots and 100 kDa in leaves, retaining about 82.90 and 74.72% of the total copper in the soluble fraction. Under Cu stress, SA induced the synthesis of 5 new polypeptides with molecular weight ranged from 204 to 26 kDa in roots and 4 new polypeptides ranged from 189 to 6 kDa in case of leaves. The results indicate that salicylic acid can alleviate the adverse effects of copper on the growth of sunflower plants by interfering of SA in translocation of Cu and/or increasing Cu-binding proteins in sunflower

The rate of germination, radicle and plumule length, fresh and dry mass of maize seedlings were increased as Ca2+ was added to the nutrient solution, which contained different levels of Cd2+, especially at low concentration of Ca2+ (5 mM) and high concentrations of Cd2+ (1.4 and 1.8 mM). The biosynthesis of pigments, respiration rate and content of soluble saccharides in endosperm were reduced sharply as the concentration of Cd2+ in the medium increased. This effects was alleviated by Ca2+ addition. Cd2+ content in seedlings was increased as the Cd2+ concentration in medium was increased and decreased sharply as Ca2+ was present in the culture medium. The study suggests liming of soil with CaCO3 to improve the yield of many crops.

The ameliorative effect of salicylic
acid (SA: 0.5 mM) on sunflower (Helianthus
annuus L.) under Cu stress (5 mg l
–1
) was studied.
Excess Cu reduced the fresh and dry weights of
different organs (roots, stems and leaves) and
photosynthetic pigments (chlorophyll a, b and
carotenoids) in four-week-old plants. There was a
considerable increase in Chl a/b ratio and lipid
peroxidation in both the roots and leaves of plants
under excess Cu. Soluble sugars and free amino
acids in the roots also decreased under Cu stress.
However, soluble sugars in the leaves, free amino
acids in the stems and leaves, and proline content
in all plant organs increased in response to Cu
toxicity. Salicylic acid (SA) significantly reduced
the Chl a/b ratio and the level of lipid peroxida-
tion in Cu-stressed plants. Under excess Cu, a
higher accumulation of soluble sugars, soluble
proteins and free amino acids including proline
occurred in plants treated with 0.5 mM SA.
Exogenous application of SA appeared to induce
an adaptive response to Cu toxicity including

The response of wheat seedlings germinated under salinity
stress to exogenous abscisic acid was discussed. Exogenous
ABA acid induces two characteristic proteins of high molecu-
lar weights ( 109.4 and 84.0 kDa) in addition to the new protein set formed under high salinity levels. ABA, also induces synthesized forms of guaiacot peroxidase in seedlings treated with 200 mM NaCI. The induction and/or accumulation of peroxi-
dase isoforms in ABA-treated seedlings, may reduce the active
oxygen produced by salinity. The changes in gene expression
and peroxidase isoforms may be selected to adaptation of
wheat seedlings to NaCl-salinity.

The effect of sewage water on some physiological activities of cyanobacteria was studied. Metal-tolerant cyanobacterium
(Nostoc linckia) and metal-sensitive (Nostoc ri6ularis) were grown at three levels of sewage water (25, 50 and 75%). The growth
rate showed significant stimulation in low and moderate levels (50% for N. linckia and 25% for N. ri6ularis). Not only the number
of cells was elevated but also, the time required to reach the exponential and the stationary phases was reduced. Also, low levels
of sewage water increased chl.a content, photosynthetic O2-evolution, respiration and protein content. Similarly, heterocyst
frequency as well as nitrogenase activity were increased in cyanobacteria grown at low and moderate levels (25 and 50% sewage).
On the other hand, the high level of waste (75%) reduced growth and metabolic activities of the two species. N. linckia
accumulated about 30-fold of Zn and ten-fold of Cd than those of growth medium (50% sewage water). Also, N. ri6ularis
accumulated about ten-fold of Zn and two-fold of Cd. The distribution of Cd and Zn in cells were investigated. About 65–60%
of Cd or Zn were found in pellets (sediment) as insoluble form in the two species. The soluble form (cytosolic fraction) after being
fractionated on sephadex G-(75-100) revealed two peaks with molecular weights of 70–75 and 40–45 kDa. These peaks were in
coincidence with Cd and Zn maxima. Nostoc ri6ulais showed more sensitivity to heavy metals than N. linckia, and accumulated
less amount of metal-binding proteins. Nostoc linckia seems to be tolerant to heavy metals (Zn and Cd) and is able to accumulate
this metal by adsorption on the pellets (cell surface) and:or through sequestration via metal-binding protein. Therefore it can be
recommended it to be employed in the purification of waste contaminated with these heavy metals. © 2000 Elsevier Science B.V.
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