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1

Accumulation and scavenging of reactive oxygen species and nitric oxide correlate with stigma maturation and pollen–stigma interaction in sunflower

100%
Sharma B., Bhatla S. C.
Acta Physiologiae Plantarum
|
2013
|
tom 35
|
nr 09
During the course of stigma development in sunflower (bud, staminate and pistillate stages), correlation is evident among the accumulation of reactive oxygen species (ROS), nitric oxide (NO), and the activities of ROS scavenging enzymes [superoxide dismutase (SOD) and peroxidase (POD)]. Confocal image analysis shows a gradual increase in ROS and NO accumulation in the stigmatic papillae, which may provide immunity to the developing stigma and function as signalling molecules. A novel, NO-specific probe (MNIP-Cu) has been employed for the detection and quantification of intracellular NO. Mn-SOD (mitochondrial) and Cu/Zn-SOD (cytoplasmic) exhibit differential expression during the staminate stage of stigma development. An increase in total SOD activity at the staminate stage is followed by a peak of POD activity during pistillate stage, thereby indicating the sequential action of the two enzymes in scavenging ROS. An increase in the number of POD isoforms is observed with the passage of stigma development (from three at bud stage to seven at pistillate stage), and two POD isoforms are unique to pistillate stage, thereby highlighting their role in ROS scavenging mechanism. ROS and NO accumulation exhibit reverse trends during pollen–stigma interaction.
2

Photomodulation of fatty acid composition and lipoxygenase activity in sunflower seedling cotyledons

100%
Yadav M., Bhatla S. C.
Acta Physiologiae Plantarum
|
2015
|
tom 37
|
nr 08
The dynamics of fatty acid composition is an important metabolic index of seed germination and seedling development process. Present investigations indicate a preferential mobilization of fatty acids, particularly linoleic acid, out of the oil bodies in sunflower seedling cotyledons. A lack of selectivity in the utilization of saturated fatty acids during seed germination is also evident. Lipoxygenase (LOX) may play a role in the reconstitution of membrane lipid composition as cells expand during seed germination. LOX activity is absent in sunflower seeds and appears during germination. Photo modulation of LOX activity is evident by its enhanced expression in lightgrown seedling cotyledons. Since sunflower LOX activity is easily solubilized by mild detergent, such as 2 % Triton X-100, the association of LOX with the membrane does not seem to be very strong unlike other membrane proteins, such as oleosins, which can be extracted only by stringent procedures. Sunflower LOX has only one pH optimum with linoleic and linolenic acids as substrates, indicating the presence of single isoform in the total soluble protein (TSP) and oil body (OB) extracts. OB-associated LOX exhibits substrate-dependent variation in its pH optima. Specific activity of TSP and OB-associated LOX increases as seedling growth progresses. Sunflower TSP-LOX activity is inhibited by some hydrophobic thiols. TSP as well as OB-associated LOX activity in sunflower cotyledons is modulated by Ca2+ availability in a negative way. A critical role of LOX is, thus, evident during seed germination in sunflower.
3

Elemental and biochemical markers of stigma receptivity in sunflower

100%
Sharma B., Bhatla S. C.
Acta Physiologiae Plantarum
|
2014
|
tom 36
|
nr 06
Stigma development in sunflower is accompanied with an accumulation of calcium (33 %), potassium (37 %) and boron (62 %) in mature stigma as compared to stigma at bud stage, thereby demonstrating their essential roles in attaining receptivity. Membrane-bound calcium accumulation is enhanced on the pellicle and is also evident in the cytoplasm accompanying stigma maturation. Total soluble carbohydrate content increases in the staminate stage (55 %) as compared to bud stage. Glucose and fructose are the major monosaccharides and their contents are maximum in the staminate stage. Total lipid content also increases with the passage of stigma development. Erucic acid (22:1) is expressed specifically in the bud and staminate stages. A variation in the contents of triacylglycerides and free fatty acids, and expression of fatty acyl esterases in mature stigma have been correlated with biochemical events associated with signalling mechanisms. Lastly, enhanced expression of two hydrolytic enzymes, namely β-1,3 glucanase and fatty acyl ester hydrolase, has been observed to correlate with stigma maturation. Present findings, thus, provide new information on the structural and biochemical changes marking various signalling events associated with successful pollen–stigma interaction.
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