The effects of nitrogen and phosphorus levels on the physiological traits, yield, and seed yield of rapeseed (Brassica napus L.), were studied in a farm research project of Zanjan University. Three levels of nitrogen (0, 100, and 200 kg/ha) and three levels of phosphorus (0, 75, and 150 kg/ha) were considered. The results showed that an increase in nitrogen level caused an increase in the leaf chlorophyll content so that the application of 200 kg/ha of nitrogen increased the chlorophyll content of the leaves until the mid-grain filling stage. Nitrogen application lowered leaf stomatal conductance in the early flowering stage whereas the stomatal conductance was increased during the late flowering stage. Nitrogen application (100 and 200 kg/ha) also increased the quantum yield of photosystem II. On the other hand, with the application of 150 kg/ha and 75 kg/ha of phosphorus, the leaf stomatal conductance and the quantum yield of photosystem II in the early flowering stage increased respectively. The results showed that the application of 200 kg/ha of nitrogen and 75 kg/ha of phosphorus significantly increased seed and oil yield compared to the control. In addition, the number of siliques per plant and the weight of 1000 seeds showed an increasing trend that was affected by nitrogen and phosphorus levels. This study demonstrated that nitrogen enhanced the chlorophyll content, leaf area, and consequently, the quantum yield of photosystem II. Nitrogen also augmented the seed filling duration, seed yield, and oil yield by increasing gas exchange. As a result, the application of 100 kg/ha of nitrogen together with 75 kg/ha phosphorus showed the greatest effect on the qualitative and quantitative yield of rapeseed. However, the application of 200 kg/ha of nitrogen alone or in combination with different levels of phosphorus did not significantly increase many of the studied traits.

The use of growth-stimulating signals to increase the tolerance of plants to water deficits can be an important strategy in the production of plants in dry areas. Therefore, a split-plot experiment with three replications was conducted to evaluate the effects of sodium nitroprusside (SNP) application rate as an NO donor (0, 100, and 200 µM) on the growth and yield parameters of Silybum marianum L. (S. marianum) under different irrigation cut-off times (control, irrigation cut-off from stem elongation, and anthesis). The results of this study showed that with increasing drought severity, leaf RWC, proline content and capitula per plant, 1000 grain weight, plant height, branch per plant, capitula diameter, and the biological and grain yield of S. marianum decreased significantly, whereas the number of grains per capitula increased compared with the control. Also, by irrigation cut-off from the stem elongation stage, the density of leaf stomata at the bottom and top epidermis increased by 64% and 39%, respectively, and the length of the stomata at the bottom epidermis of the leaf decreased up to 28%. In contrast, the results of this experiment showed that the exogenous application of nitric oxide reduced the negative effects of irrigation cut-off, such that the application of 100 µM SNP enhanced RWC content (up to 9%), proline concentration (up to 40%), and grain (up to 34%) and biological (up to 44%) yields in plants under drought stress compared with non-application of SNP. The decrease in the number of capitula per plant and capitula diameter was also compensated by foliar application of 100 µM SNP under stress conditions. In addition, exogenous NO changed the behavior of the stomata during the period of dehydration, such that plants treated with SNP showed a decrease in the stomatal density of the leaf and an increase in the length of the stomata at the leaf bottom epidermis. These results indicate that SNP treatment, especially at 100 µM, was helpful in alleviating the deleterious effects of water deficiency and enhancing the tolerance of S. marianum to withholding irrigation times.

Nitric oxide (NO) is recognized as an endogenous signaling molecule that plays an important role in the defence responses of medicinal plants to NaCl stress. In this study, we investigated the effects of sodium nitroprusside (SNP) as an NO donor at three concentrations (0, 100, and 200 µmol l⁻¹) to alleviate the deleterious effects of salt stress (100 mM NaCl) on leaf gas exchange and biochemical characteristics of Silybum marianum L. seedlings. This study showed that salt stress significantly decreased relative water content (RWC), chlorophyll b content, endogenous NO concentration, maximum quantum yield (Fv/Fm), leaf gas exchange, stomatal size, K⁺/Na⁺ ratio, and plant dry weight, and increased malondialdehyde (MDA) content, hydrogen peroxide (H₂O₂) content, proline content, stomatal density, and enzyme activities. SNP treatment increased Fv/Fm, photosynthetic pigments, K⁺/Na⁺ ratio, and dry weights of the shoots and roots of NaCl-exposed plants. The exogenous application of NO increased the proline content under salinity stress more than under stress conditions without SNP application, so that the proline content increased from 32 to 47 µmol g⁻¹. Application of 100 µM SNP also increased endogenous NO concentration (up to 43%) and consequently protected plants against salt stress-induced damage by improving enzyme activity and reducing the H₂O₂ generation rate (up to 14%) and MDA content (up to 50%) compared to plants treated with NaCl alone. Foliar application of NO to salt-stressed plants increased root and shoot respiration rates from 20 and 12%, respectively, under salinity stress to 57% under the application of SNP and stress conditions, and decreased stomatal conductance by up to 70%, resulting in improved RWC. Increased internal NO generation in plants induced by 100 µM SNP application has the potential to mitigate salinity injury in Silybum marianum L. plants.

The main source of seed filling results from the photosynthesis of the green tissue closest to the seed sinks in the capitula. To evaluate the role of different leaf strata and capitula in seed yield and its components of Safflower genotypes, a field study was performed as a factorial experiment based on RCBD in 3 replicates in East Azarbaijan Agricultural and Natural Resources Research and Education Center in 2008. The used factors in this experiment were: two Safflower genotypes including (Mahalli Esfahan and Goldasht) and defoliation in five levels: defoliation of plants in lower 1/3, middle 1/3, upper 1/3 of the stem, capitulum covered with aluminum paper and control (without defoliation). The results showed that defoliation did not affect plant height and number of pods. But, there was a highly significant difference between strata in terms of number of seeds per pod, number of seeds per plant, 1000 seeds weight, oil percentage and oil yield. The interaction of genotype×strata treatments in seeds yield and harvest index was significant. Among the defoliation treatment levels in both genotypes, the highest decrease in the seed yield compared to the control were observed in the upper 1/3 defoliation levels, whereas the lowest decrease was observed in the lower 1/3 defoliation level. The rate of seed yield reduction in Mahalli Esfahan was higher than Goldasht. The change in Goldasht seed yield was mostly due to changes in the number of seeds per plant and the number of seeds in the head. In addition, net photosynthesis, strata leaf area, and photosynthesis contribution of the upper strata compared to the lower ones were higher, and removal of the upper strata had the highest effect on seed yield through the reduction in the total photosynthesis of the whole plant. Also, covering the capitulum caused a significant decrease in the seed yield. So, head photosynthesis has a major contribution to Safflower seed yield.