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

Abstract

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 Ca 2? availability in a negative way. A critical role of LOX is, thus, evident during seed germination in sunflower.

Salt-tolerant and -sensitive seedlings exhibit noteworthy differences in lipolytic events in response to salt stress

“…The pattern of gradual decline in total neutral lipids from seedling cotyledons raised in control conditions upto 6 days of growth is similar to past observations from Delhi University on a semi-tolerant sunflower variety (KBSH 53). 11 However, in the present case, raising seedlings of salt-tolerant and salt-sensitive varieties in the presence of 120 mM NaCl revealed greater retention of total lipids in saltsensitive variety than in salt-tolerant one, in response to salt stress. Present observations highlight significance of salt-sensitivity for retention of total neutral lipids.…”

“…In sunflower seedling cotyledons, LOX activity is evident both on OB membranes and in the cytosol although its major fraction resides in cytosol. 11 Present investigations have demonstrated enhanced LOX activity and its further upregulation under salt stress in saltsensitive sunflower seedlings. Salt-tolerance, on the contrary, appears to correlate with lower LOX activity, irrespective of salt stress.…”

“…9,10 Earlier work from Delhi University has demonstrated that LOX activity is not detectable in ungerminated sunflower seeds but it subsequently becomes detectable in seedling cotyledons, hypocotyls, and roots. 11 Changes in LOX activity during seedling growth are further modulated by light and calcium in seedling cotyledons. In sunflower seedling cotyledons, LOX activity is evident both on OB membranes and in the cytosol although its major fraction resides in cytosol.…”

“…In this context, it may be noted that LOX in Arabidopsis exhibits almost 2.5 times higher activity with linolenic acid (18:3 Δ 9, 12, 15 ) as compared with linoleic acid. 12 On the other hand, low LOX activity in salttolerant sunflower seedlings could possibly be explained as a response to noteworthy changes in the calcium ion content of tissue since LOX is known to be regulated by calcium in a negative way not only in sunflower seedlings 11 but also in Vigna unguiculata and in cucumber. 13,14 PA is one of the primary signaling molecules involved in the complex network of lipid signaling under stress conditions, such as drought and salt stress.…”

Physiological Adaptive Strategies of Oil Seed Crop Ricinus communis Early Seedlings (Cotyledon vs. True Leaf) Under Salt and Alkali Stresses: From the Growth, Photosynthesis and Chlorophyll Fluorescence

“…Storage substances in this type of cotyledon include a considerable amount of protein, lipids, and polysaccharides (Huang, 1996; Golombek et al, 2001; Hills, 2004). Mobilization of the storage substances from cotyledons can provide amino acid (for de novo protein synthesis), fatty acid (for energy), and starch (the most common form of stored carbohydrate for respiration) to the seedlings (Bewley and Black, 1994; Tan-Wilson and Wilson, 2012; Yadav and Bhatla, 2015). However, few studies focused on the photosynthetic activity of plant cotyledon, which is quite important during seedling establishment stage.…”