Abstract Environmental signals drive seed dormancy cycling in the soil to synchronize germination with the optimal time of year, a process essential for species' fitness and survival. Previous correlation of transcription profiles in exhumed seeds with annual environmental signals revealed the coordination of dormancy‐regulating mechanisms with the soil environment. Here, we developed a rapid and robust laboratory dormancy cycling simulation. The utility of this simulation was tested in two ways: firstly, using mutants in known dormancy‐related genes [DELAY OF GERMINATION 1 (DOG1), MOTHER OF FLOWERING TIME (MFT), CBL‐INTERACTING PROTEIN KINASE 23 (CIPK23) and PHYTOCHROME A (PHYA)] and secondly, using further mutants, we test the hypothesis that components of the circadian clock are involved in coordination of the annual seed dormancy cycle. The rate of dormancy induction and relief differed in all lines tested. In the mutants, dog1‐2 and mft2, dormancy induction was reduced but not absent. DOG1 is not absolutely required for dormancy. In cipk23 and phyA dormancy, induction was accelerated. Involvement of the clock in dormancy cycling was clear when mutants in the morning and evening loops of the clock were compared. Dormancy induction was faster when the morning loop was compromised and delayed when the evening loop was compromised.

Seeds have evolved to be highly efficient environmental sensors that respond not only to their prevailing environment, but also their environmental history, to regulate dormancy and the initiation of germination. In the present work we investigate the combined impact of a number of environmental signals (temperature, nitrate, light) during seed development on the mother plant, during post-shedding imbibition and during prolonged post-shedding exposure in both dry and imbibed states, simulating time in the soil seed bank. The differing response to these environments was observed in contrasting winter (Cvi, Ler) and summer (Bur) annual Arabidopsis ecotypes. Results presented show that environmental signals both pre- and post-shedding determine the depth of physiological dormancy and therefore the germination response to the ambient environment. The ecotype differences in seed response to ambient germination conditions are greatly enhanced by seed maturation in different environments. Further variation in response develops following shedding when seeds do not receive the full complement of environmental signals required for germination and enter the soil seed bank in either dry or imbibed states. Species seed dormancy characteristics cannot therefore be easily defined, as seed dormancy is a dynamic state subject to within-species adaptation to local environments.

Polyphenol oxidases (PPOs) are active during germination of seeds in which the activites may be effected by environmental factors. This study was conducted to determine the effect of boron (B), an important nutrient in phenolic metabolism. on PPOs in embryo and endosperm fractions of two wheat varieties during germination. Seeds were subjected to various concentration of B for 24 h. The germination percentage of both wheat cultivars was not affected by boron concentrations up to 50 mM, and decreased by 100 mM and 150 mM. The lower boron concentrations (0, 0.1 and 50 ITEM) increased PPOs activity at the beginning of germination up to 6- 9 h whereas its excess levels (100 and 150 mM) decreased PPOs in embryo and endosperm during germination of both cultivars. Dopa and caffeic acid oxidasing PPOs had more activity in embryo and endosperm of drought resistant genotype Kirac-66 in all treatments as compared with those in susceptible Sultan-95. The PPO activities in both embryo and endosperm tissues of Kirac-66 seeds showed a similar occurrence, but the activities in embryos of Sultan-95 seeds were higher than endosperm. The findings suggest that wheat seeds having high PPO activity during germination in both embryo and endosperm fractions may tolerate B stress better than the seeds exhibiting low PPO activity.

Starch is the main product of photosynthesis and its the most dominant reserve polysaccaride that stored in photosynthetic and non-photosynthetic tissues. Starch is a staple food in human and animal diets, but also a raw material widely used for industrial purposes, such as food, paper and textile. Starch granule structure, amylose and amylopectin moleculer structure, amylose and amylopectin ratio, and also lipid, protein and phosphate content are the main determinants that effect the functional properties of starch, in turn, its industrial application. For example, in food industry high amylose starches are prefered in sweet and fried products, while amylose free starches are used in frozen foods. In fact, starch is generally modified by physical, enzymatic or chemical treatments to alter structural and functional properties for endustrial applications. Today starches with improved functionality has also been produced from mutant and genetically modified plants. Increased knowledge about enzymes that are involved in starch biosynthesis and improvement in plant biotechnology made possible to alter starch composition by genetic modifications. This rewiev focus on the starch granule structure, starch biosynthetic enzymes in storage tissues and their genetic modifications with potantial benefits.

Starch is the main product of photosynthesis and its the most dominant reserve polysaccaride that stored in photosynthetic and non-photosynthetic tissues. Starch is a staple food in human and animal diets, but also a raw material widely used for industrial purposes, such as food, paper and textile. Starch granule structure, amylose and amylopectin moleculer structure, amylose and amylopectin ratio, and also lipid, protein and phosphate content are the main determinants that effect the functional properties of starch, in turn, its industrial application. For example, in food industry high amylose starches are prefered in sweet and fried products, while amylose free starches are used in frozen foods. In fact, starch is generally modified by physical, enzymatic or chemical treatments to alter structural and functional properties for endustrial applications. Today starches with improved functionality has also been produced from mutant and genetically modified plants. Increased knowledge about enzymes that are involved in starch biosynthesis and improvement in plant biotechnology made possible to alter starch composition by genetic modifications. This rewiev focus on the starch granule structure, starch biosynthetic enzymes in storage tissues and their genetic modifications with potantial benefits.

Poplar trees sustain close to the predicted increase in leaf photosynthesis when grown under long-term elevated CO2 concentration ([CO2]). To investigate the mechanisms underlying this response, carbohydrate accumulation and protein expression were determined over four seasons of growth. No increase in the levels of soluble carbohydrates was observed in the young expanding or mature sun leaves of the three poplar genotypes during this period. However, substantial increases in starch levels were observed in the mature leaves of all three poplar genotypes grown in elevated [CO2]. Despite the very high starch levels, no changes in the expression of photosynthetic Calvin cycle proteins, or in the starch biosynthetic enzyme ADP-glucose pyrophosphorylase (AGPase), were observed. This suggested that no long-term photosynthetic acclimation to CO2 occurred in these plants. Our data indicate that poplar trees are able to 'escape' from long-term, acclimatory down-regulation of photosynthesis through a high capacity for starch synthesis and carbon export. These findings show that these poplar genotypes are well suited to the elevated [CO2] conditions forecast for the middle of this century and may be particularly suited for planting for the long-term carbon sequestration into wood.

The effects of geothermal waters (GW) on the seed germination and seedling growth of wheat (Triticum aestivum L. cv. Atay-85) at various salt (NaCl) concentrations were examined. It was found that 150 mM NaCl decreased significantly both seed germination and seedling growth of wheat. Salt stress of seed germination and seedling growth of wheat were alleviated by GWs of Sefakoy and Murat Dagi but it was not by GW Sarikiz. The highest alleviation effect was found with GW Murat Dagi and the effect was attributed to its calcium richness and lower level of toxic elements.

The response of net photosynthetic CO(2) uptake (A) to increasing leaf intercellular CO(2) concentration (c(i)) was determined in antisense Nicotiana tabacum plants, derived from six independent transformation lines, displaying a range of sedoheptulose-1, 7-bisphosphatase (SBPase) activities. The maximum in vivo ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation (V(c,max)) and RuBP regeneration (J(max)) rates were calculated from the steady-state measurements of the A to c(i) response curves. In plants with reductions in SBPase activity of between 9% and 60%, maximum RuBP regeneration capacity declined linearly (r(2)=0.79) and no significant change in apparent in vivo Rubisco activity (V(c,max)) was observed in these plants. No correlation between V(c,max) and a decrease in capacity for RuBP regeneration was observed (r(2)=0.14) in the SBPase antisense plants. These data demonstrate that small decreases in SBPase activity limit photosynthetic carbon assimilation by reducing the capacity for RuBP regeneration.

We present observations of photosynthetic carbon dioxide assimilation, and leaf starch content from genetically modified tobacco (Nicotiana tabacum) plants in which the activity of the Calvin cycle enzyme, sedoheptulose-1,7-bisphosphatase, is reduced by an antisense construct. The measurements were made on leaves of varying ages and used to calculate the flux control coefficients of sedoheptulose-1,7-bisphosphatase over photosynthetic assimilation and starch synthesis. These calculations suggest that control coefficients for both are negative in young leaves, and positive in mature leaves. This behaviour is compared to control coefficients obtained from a detailed computer model of the Calvin cycle. The comparison demonstrates that the experimental observations are consistent with bistable behaviour exhibited by the model, and provides the first experimental evidence that such behaviour in the Calvin cycle occurs in vivo as well as in silico.

The application of genetic engineering to agricultural production has resulted in a number of transgenic plants, that were transformed with a foreign gene. To date around 4500 transgenic plants have been tested in the field and about 40 transgenic crops including maize, soybean, cotton, tomato and potatoes have been released and growed commercially. In particular, herbicide resistant and insect resistant species have increased the crop productivity. In addition transgenic plants with improved abiotic stress tolerance are also offering great opportunity for crop production by enabling them to survive in extrem environments. This review gives some examples of transgenic crops which have been commercialized and also discusses the positive and negative features of these plants.

The impact of reduced sedoheptulose-1,7-bisphosphatase (SBPase) activity on photosynthetic capacity and carbohydrate status was examined during leaf expansion and maturation in antisense transgenic tobacco (Nicotiana tabacum L. cv Samsun) plants. In wild-type plants, photosynthetic capacity was lowest in young expanding leaves and reached a maximum in the fully expanded, mature leaves. In contrast, the transgenic antisense SBPase plants had the highest photosynthetic rates in the young expanding leaves and lowest rates in the mature leaves. In the mature, fully expanded leaves of the transgenic plants photosynthetic capacity was closely correlated with the level of SBPase activity. However, in the youngest leaves of the SBPase antisense plants, photosynthetic rates were close to, or higher than, those observed in wild-type plants, despite having a lower SBPase activity than the equivalent wild-type leaves. Reductions in SBPase activity affected carbohydrate levels in both the mature and young developing leaves. The overall trend was for decreased SBPase activity to lead to reductions in carbohydrate levels, particularly in starch. However, these changes in carbohydrate content were also dependent on the developmental status of the leaf. For example, in young expanding leaves of plants with the smallest reductions in SBPase activity, the levels of starch were higher than in wild-type plants. These data suggest that the source status of the mature leaves is an important determinant of photosynthetic development.

Sedoheptulose‐1,7‐bisphosphatase (SBPase; EC 3.1.3.37) catalyses the dephosphorylation of sedoheptulose‐1,7‐bisphosphate in the regenerative phase of the Calvin cycle. Antisense plants with reduced levels of SBPase have decreased photosynthetic capacity and altered carbohydrate status, leading to modifications in growth and development. The catalytic activity of SBPase is regulated by light via the ferredoxin/thioredoxin system. Recently, the amino acids within the SBPase protein involved in this regulatory mechanism have been identified and a deregulated, permanently active form of the enzyme has been produced using site‐directed mutagenesis. This paper explores how transgenic Nicotiana tabacum cv. Samsun plants, containing the deregulated form of the SBPase enzyme, may lead to a better understanding of the in vivo role of light activation of this important Calvin cycle enzyme.

Plants are a major source of vitamins and micronutrients that required in human diet. However main food crops are usually deficient in important nutrients such as vitamins and microelements that deficiencies can cause series health problems. Biotechnology research has already demonsrated its potantial in enhancing the nutritional quality of our food. At this point, transgenic plants with enhanced provitamin A, vitamin C, vitamin E and ferritin content are promising for solving nutrition problems for human health. This review briefly summarise commercially grown transgenic crops and concentrates on new transgenic crops with enhanced nutritive value that might commercialized in near future.