Asparagine Enhances Starch Accumulation in Developing and Germinating Lupin Seeds
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Asparagine Enhances Starch Accumulation in Developing and Germinating Lupin Seeds Sławomir Borek • Agnieszka Galor Ewelina Paluch
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Received: 3 May 2012 / Accepted: 7 November 2012 / Published online: 16 January 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract Regulation of starch accumulation in yellow (Lupinus luteus L.), white (L. albus L.), and Andean lupin (L. mutabilis Sweet) developing and germinating seeds was investigated. Research was conducted on cotyledons isolated from developing seeds as well as on organs of germinating seeds, that is, isolated embryo axes, excised cotyledons, and seedling axes and cotyledons. All organs were cultured in vitro for 96 h in different carbon (60 mM sucrose) and nitrogen (35 mM asparagine or 35 mM nitrate) conditions. Ultrastructure observation showed one common pattern of changes in the number and size of starch granules caused by sucrose, asparagine, and nitrate in both developing and germinating seeds. Sucrose increased the number and size of starch granules. Asparagine additionally increased starch accumulation (irrespective of sucrose nutrition) but nitrate had no effect on starch accumulation. Asparagine treatment resulted in a significant decrease in soluble sugar level in all organs of germinating lupin seeds of the three species investigated. The above-mentioned changes were most clearly visible in white lupin organs. In white lupin, starch granules were visible even in cells of sucrose-starved isolated embryo axes where advanced autophagy occurs. The importance of asparagine-increased starch content in the creation of a strong source–sink gradient in developing and germinating lupin seeds is discussed. Keywords Legume Nitrate Nonstarch seeds Source–sink Sucrose Ultrastructure
S. Borek (&) A. Galor E. Paluch Department of Plant Physiology, Adam Mickiewicz University, ul. Umultowska 89, 61-614 Poznan´, Poland e-mail: [email protected]
Introduction Mature and dry lupin seeds do not contain starch (Hedley 2001; Borek and others 2006, 2011; Duranti and others 2008). However, starch is transiently accumulated in developing lupin seeds (Pinheiro and others 2005; Borek and others 2009) and disappears during seed maturation. A very similar transient starch accumulation is also observed in developing Medicago truncatula (Djemel and others 2005), Brassica napus (Da Silva and others 1997), and Arabidopsis oil seeds (Hills 2004; Baud and others 2008). Carbohydrate content in mature lupin seeds is about 36.5 % and the basic carbohydrates are oligosaccharides and fiber (Hedley 2001). In contrast to lupin seeds, starch content in mature pea seeds may reach 50 % of dry matter (Gallardo and others 2008). The main storage compound in mature lupin seeds is protein, especially globulins called conglutins (Ratajczak and others 1999). Protein content in lupin seeds may reach up to 50 % of dry matter (Borek and others 2012a), whereas lipid level in lupin seeds may vary from a few to about 20 % (Borek and others 2009, 201
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