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Biosynthesis and accumulation of flavonolignans in plants are influenced by different environmental conditions. Biosynthesis and accumulation of silymarin in milk thistle (Silybum marianum L.) were studied under drought stress with respect to the antioxidant defense system at the physiological and gene expression level. The results revealed a reduction in leaf chlorophyll, ascorbic acid, and glutathione contents. In contrast, H2O2, proline, and antioxidative enzyme activities, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), were increased. These results confirmed that milk thistle undergoes oxidative stress under drought stress. Furthermore, transcription levels of APX, SOD, CAT, 1-Cys-Prx, and PrxQ were significantly increased in milk thistle under drought stress. Overall this suggests that protection against reactive oxygen species and peroxidation reactions in milk thistle are provided by enzymatic and non-enzymatic antioxidants. Flavonolignans from milk thistle seeds after different drought treatments were quantified by high-performance liquid chromatography (HPLC) and showed that severe drought stress enhanced the accumulation of silymarin and its components compared with seeds from the control (100% water capacity). Silybin is the major silymarin component and the most bioactive ingredient of the milk thistle extract. Silybin accumulation was the highest among all silymarin components in seeds obtained from drought-stressed plants. The expression of the chalcone synthase (CHS) genes (CHS1, CHS2, and CHS3), which are associated with the silybin biosynthetic pathway, was also increased during drought stress. These results indicated that milk thistle exhibits tolerance to drought stress and that seed derived from severe drought-stressed plants had higher levels of silymarin.

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Insect damage in canola adversely affects its productivity andquality and is considered one of the most important degrading factors in Egypt. The effect of foliar application of salicylic acid (SA) on aphid populations, growth and yield of canola (Brassica napus, L.) cv. serw 4 was the major goal of this study. Two experiments were conducted at the farm of Faculty of Agriculture, Suez Canal University, Ismailia, Egypt, during 2014 and 2015 seasons, to achieve this target. Each experiment included four levels of SA (0, 50, 100, 200 mg 1-1). The experimental results revealed that SA, at low concentration (50 mg 1-1), was an effective treatment for reduction the number of aphid populations and colony depth on the main inflorescence, contributed with reducing the thickness of secretory tissue of flower pedicel. The level of 50 mg 1-1 of SA-treated canola had the highest number of stomata cm-2, along with the lowest width of both stoma and its aperture. Thickness of xylem tissue and the number of xylem vessels bundle-1 in leaf midrib, reducing sugars and free amino acids was increased at 50 mg 1-1 SA, but free phenolics content did not affected significantly. Under controlled conditions, changes in temperature of infected leaves allowed the discrimination between healthy and infected areas in thermo-image, even before visible symptoms of aphid infestation appeared. The detection of modifications in plants or canopies, associated with low insect severity in the early stages of infestation, was crucial for the targeted, site-specific or on demand application of integrated aphid control. Canola, which was treated with 50 mg 1-1 of SA, gave 30.5 and 27.9 kg of oil ha-1 over the control. It was concluded that spraying of SA at 50 mg 1-1 was an effective elicitor to diminish the aphid numbers on canola inflorescence and improve its yield.

Plants have evolved complex mechanisms to mitigate osmotic and ionic stress caused by high salinity. The effect of exogenous spermine (Spm) and spermidine (Spd) on defence responses of wheat seedlings under NaCl stress was investigated by measuring antioxidant enzyme activities and the transcript expression of corresponding genes. Exogenous Spm and Spd decreased the level of malondialdehyde, increased chlorophyll and proline contents, and modulated PSII activity in wheat seedlings under salt stress. Spermidine alleviated negative effects on CO2 assimilation induced by salt stress in addition to significantly increasing the activity and content of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). It appears Spd conferred salinity tolerance in wheat seedlings by enhancing photosynthetic capacity through regulation of gene expression and the activity of key CO2 assimilation enzymes. Exogenous Spm regulated activities of different antioxidant enzymes (catalase, glutathione reductase, dehydroascorbate reductase, ascorbate peroxidase, and superoxide dismutase) and efficiently modulate their transcription levels in wheat seedlings under salt stress. It is likely that Spm plays a key role in alleviating oxidative damage of salt stress by adjusting antioxidant enzyme activities in plants. In addition, exogenous Spd increased transcript level of spermine synthase under salt stress. Salinity stress also caused an increase in transcript levels of diamine oxidase (DAO) and polyamine oxidase (PAO). Exogenous Spd application resulted in a marked increase in free Spd and Spm contents under saline conditions. These results show that exogenous Spd and Spm effectively upregulated transcriptional levels of antioxidant enzyme genes and improved the defence response of plants under salt stress.