Difference and Its Mechanism in Tolerance to Low-Potassium between Liaomian 18 and NuCOTN99B at Seedling Stage

Abstract

Exploiting genetic diversity of cotton in tolerance to low-potassium (K) is desired for sustainable production. The objective of the present study was to compare the variation in tolerance to low-K between Liaomian 18, a non-insect-resistant cotton cultivar, and NuCOTN99B, a transgenic insect-resistant cotton cultivar from American, hydroponically grown in growth chamber and to elucidate the underlying mechanisms controlling that. When K application was sufficient (2.5 mmol L −1 ), there was no significant difference in dry matter yield between the two cultivars at seedling-stage. However, Liaomian 18 produced 170% more dry matter than NuCOTN99B under low K (0.03 mmol L −1 ) growing condition, suggesting that Liaomian 18 is K-efficiency with higher tolerance to low-K and NuCOTN99B is K-inefficiency. It was observed that K uptake amount per unit root dry weight, per unit root length and per unit root surface area in Liaomian 18 was similar to or lower than that in NuCOTN99B, implying that the K uptake ability concerning physiological aspect of Liaomian 18 was not superior. Furthermore, the ratio of K accumulation in leaf to that in whole plant was 57.7% for Liaomian 18, and 67.6% for NuCOTN99B, which suggested that the K translocation efficiency in Liaomian 18 was ineffective, when compared to NuCOTN99B. Nevertheless, Liaomian 18 had a large root system; its root length, root surface area and root volume were equal to 3.4-, 3.8-, and 4.2-fold of those of NuCOTN99B, respectively. Moreover, the index of K utilization (dry matter produced per unit of K concentration) in Liaomian 18 was 147% higher than that in NuCOTN99B. Therefore, the high tolerance to low-K of Liaomian 18 possibly depended on its large root system and efficient internal K utilization instead of its K uptake ability per unit of root dry weight/length/surface area and K translocation efficiency in plant. Because there were no significant differences in osmotic potential as well as relative water content in leaf between Liaomian 18 and NuCOTN99B, it was concluded that the difference in internal K utilization efficiency between the two cultivars was not related to the biophysical function of K (regulation of turgor pressure and osmotic potential), but likely related to the biochemical function of K (promotion of photosynthesis, phloem loading, and protein synthesis etc.).