Abstract
The major seed storage reserves in oilseeds are accumulated in protein bodies and oil bodies, and serve as an energy, carbon, and nitrogen source during germination. Here, the spatio-temporal relationships between protein bodies and several key enzymes (phospholipase A, lipase, and lipoxygenase) involved in storage lipid mobilization in cotyledon cells was analysed during in vitro seed germination. Enzyme activities were assayed in-gel and their cellular localization were determined using microscopy techniques. At seed maturity, phospholipase A and triacylglycerol lipase activities were found exclusively in protein bodies. However, after seed imbibition, these activities were shifted to the cytoplasm and the surface of the oil bodies. The activity of neutral lipases was detected by using α-naphthyl palmitate and it was associated mainly with protein bodies during the whole course of germination. This pattern of distribution was highly similar to the localization of neutral lipids, which progressively appeared in protein bodies. Lipoxygenase activity was found in both the protein bodies and on the surface of the oil bodies during the initial phase of seed germination. The association of lipoxygenase with oil bodies was temporally correlated with the appearance of phospholipase A and lipase activities on the surface of oil bodies. It is concluded that protein bodies not only serve as simple storage structures, but are also dynamic and multifunctional organelles directly involved in storage lipid mobilization during olive seed germination.
Highlights
Seed germination is accompanied by intense metabolic activity of cells, including respiration and protein synthesis, as well as multiple cell divisions, cell elongation, and complex structural changes at the subcellular level
Up to seven different lipolytic bands were observed in the total (Fig. 1A) and cytoplasmic fraction (Fig. 1B), with molecular weights ranging from 90 kDa to 30 kDa
The present results indicate that lipase present in protein bodies (PBs) could act by facilitating the metabolism of storage lipids in PBs during seed germination
Summary
Seed germination is accompanied by intense metabolic activity of cells, including respiration and protein synthesis, as well as multiple cell divisions, cell elongation, and complex structural changes at the subcellular level. Seed storage proteins (SSPs) are degraded during germination and used for seedling growth. These proteins provide carbon, nitrogen, and sulphur resources for subsequent seedling development (Müntz, 1996; Herman and Larkins, 1999). SSPs are accumulated during seed maturation in the protein storage vacuoles (PSVs) of the embryo and endosperm cells. At the late stage of seed maturation, the PSVs are transformed into protein bodies (PBs), which are surrounded by a membrane derived from the vacuolar membrane (Hara-Nishimura et al, 1987; Strzałka et al, 1995). Seed storage triacylglycerols (TAGs) are accumulated in the embryo and endosperm during seed development and provide the sources of carbon and energy for germination
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