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Present findings hypothesize that salt-tolerant and -sensitive oilseed plants are expected to exhibit deviant patterns of growth through lipolytic events in seedling cotyledons. It reports the growth response and different lipolytic mechanisms operating during oil body (OB) mobilization in the seedling cotyledons of salt-tolerant (DRSH 1) and salt-sensitive (PSH 1962) varieties of sunflower (Helianthus annuus L.). Salt tolerance or sensitivity to 120 mM NaCl correlates with high proteolytic degradation of OB membrane proteins, particularly oleosins, whereas salt-sensitive seedling cotyledons exhibit negligible proteolytic activity, thereby retaining OB membrane integrity for a longer time. High lipoxygenase (LOX) activity and its further upregulation by salt stress are the unique features of salt-sensitive sunflower seedlings. Salt-tolerant seedling cotyledons exhibit noteworthy modulation of phospholipase-D (PLD) activity by salt stress. Salt-sensitive seedling cotyledons exhibit higher lipase activity than saltsensitive ones and enzyme activity is downregulated by salt stress. Salt-sensitive variety exhibits higher lipid accumulation and faster lipid mobilization with seedling development than salt-tolerant variety. Accumulation of oleic and linoleic acid in the seedling cotyledons of salt-tolerant and sensitive varieties exhibits differential sensitivity to salt stress. Novel detection of hexanoic acid (6:0) is a noteworthy feature as a response to salt stress in salt-sensitive variety. These findings, thus, provide new information on long-distance salt stress sensing mechanisms at seedling stage of plant development.

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Sunflower plants are semi-tolerant to salt stress. Calcium modulates the expression of oubain-sensitive ATPases, responsible for sodium fluxes in cells. Salt stress delays degradation of oil body (OB) membrane proteins. Serotonin and melatonin contents are elevated in response to salt stress. Melatonin can detoxify the seedlings of elevated reactive oxygen species (ROS) levels. Enhanced nitric oxide (NO) expression correlates with NaCl-induced modulation of seedling growth. Salt stress enhances S-nitrosylation of cytosolic proteins in seedling cotyledons, while in roots, denitrosylation of proteins is observed. Lipid peroxide content and glutathione peroxidase (GPX4) activity are enhanced in response to salt stress. Salt stress downregulates the activity of superoxide dismutase (SOD) and upregulates the activity of GPX4 and glutathione reductase (GR). Heme oxygenase-1 (HO-1) abundance in cells surrounding the secretory canal in seedling cotyledons is enhanced in response to salt stress. NO negatively regulates the total glutathione homeostasis and regulates polyamine and glycine betaine homeostasis in response to salt stress. An intricate biochemical crosstalk is thus observed to control salt tolerance mechanisms in sunflower.

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