Abstract
Consistent with reports on other plants we recently reported that a potato transgenic line (AT010901) overexpressing sCAX1 show classic symptoms of calcium deficiency shoot tip injury, leaf curling, leaf margin necrosis and tuber internal defects such as hollow heart and brown spots. The present study was undertaken to quantify calcium in various fraction of leaf and tuber tissues of this transgenic and wild type potato clones to understand the development of these deficiency symptoms at normal calcium nutrition (1mM) and its mitigation at higher calcium nutrition (10mM). Plants were grown in controlled environment growth chamber and watered with balanced nutrient solution containing either 1 or 10 mM calcium. The plants overexpressing sCAX1 showed calcium deficiency symptoms while sequestering calcium in the vacuole as calcium oxalate crystals. Various fractions of calcium were qualified in the young and mature leaves as well as tuber tissue. A reduced concentration of water soluble fraction of calcium was most important factor related to the development of calcium deficiency symptoms in the line overexpressing sCAX1. Furthermore, an increase in this fraction appear to explain the alleviation of the deficiency symptoms in these transgenic plants.Ours is the first study to document the significance of water-soluble calcium in the development of calcium-deficiency symptoms in the potato transgenic lines overexpressing sCAX1. Furthermore, our result demonstrates that an increase in this fraction plays a significant role in the alleviation of calcium deficiency symptoms when calcium concentration in the nutrient media is increased. These results provide important insight on the role of sCAX1 in the calcium homeostasis.
Highlights
As an essential plant macro-nutrient, calcium plays a vital role in plant growth and human health
Results of our study indicate that overexpression of cation exchanger 1 (sCAX1) results in classic symptoms of calcium deficiency in leaves and tubers (Figure 1)
These symptoms occurred even though the total calcium concentration was greater in thetransgenic plants than the wild type in young leaves (Figure 3), mature leaves (Figure 5) and tubers (Figure 8) of the transgenic plants at 1 mM calcium treatment
Summary
As an essential plant macro-nutrient, calcium plays a vital role in plant growth and human health. If the level of calcium associated with membranes is reduced, those membranes can become leaky, resulting in the loss of cellular salt and organic compounds (Arora and Palta, 1988; Palta, 2010). By binding pectins in the middle lamella, calcium is a component of the cell wall and is essential for strengthening its structure (Matoh and Kobayashi, 1998; Cosgrove, 2005). Calcium moves with water in the xylem, and very little water moves to tuber and fruit tissues compared to leaf tissue. Calcium concentrations are much greater in foliage than in tubers or fruit, which can cause blossom-end rot or tuber internal defects (Kleinhenz et al, 1999; Chung et al, 2010)
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