Physiological Responses to Mineral-Excessive Conditions: Mineral Uptake and Carbohydrate Partitioning in Tomato Plants

Abstract

The shortage or surplus of minerals directly affects overall physiological metabolism of plants; especially, it strongly influences carbohydrate metabolism as a primary response. We have studied mineral uptake, synthesis and partitioning of soluble carbohydrates, and the relationship between them in N, P or K-excessive tomato plants, and examined the interaction between soluble carbohydrates and mineral elements. Four-weeks-old tomato plants were grown in a hydroponic growth container adjusted with excessive N (<TEX>$20.0mmol\;L^{-1}$</TEX> <TEX>$Ca(NO_3)2{\cdot}4H_2O$</TEX> and <TEX>$20.0mmol\;L^{-1}$</TEX> <TEX>$KNO_3$</TEX>), P (<TEX>$2.0mmol\;L^{-1}$</TEX> <TEX>$KH_2PO_4$</TEX>), and K (<TEX>$20.0mmol\;L^{-1}$</TEX> <TEX>$KNO_3$</TEX>), respectively, for 30 days. Shoot growth rates were significantly influenced by excessive N or K, but not by excessive P. The concentrations of water soluble N (nitrate and ammonium), P and K were clearly different with each tissue of tomato plants as well as the mineral conditions. The NPK accumulation in all treatments was as follows; fully expanded leaves (48%) > stem (19%) = roots (16%) = petioles (15%) > emerging leaves (1). K-excessive condition extremely contributed to a remarkable increase in the ratio, which ranged from 2.79 to 10.34, and particularly potassium was dominantly accumulated in petioles, stem and roots. Fresh weight-based soluble sugar concentration was the greatest in NPK-sufficient condition (<TEX>$154.8mg\;g^{-1}$</TEX>) and followed by K-excessive (141.6), N-excessive (129.2) and P-excessive (127.7); whereas starch was the highest in K-excessive (<TEX>$167.0mg\;g^{-1}$</TEX>) and followed by P-excessive (146.1), NPK-sufficient (138.2) and N-excessive (109.7). Soluble sugar showed positive correlation with dry weight-based total N content (p<0.01) whereas was negatively correlated with soluble P (p<0.01) and dry weight-based total P (p<0.01). On the other hand, starch production was negatively influenced by total N (p<0.001), but, it showed positive relation with total K concentration (p<0.05). This study shows that uptake pattern of NPK and production and partitioning of soluble carbohydrate were substantially different from each mineral, and the relationship between water soluble- and dry weight-based-mineral was positive.