辽棉18与新棉99B苗期耐低钾能力的差异及其机制

在室内液培(1/4改良Hoagland营养液)条件下比较了非抗虫棉辽棉18和转Bt基因抗虫棉新棉99B苗期耐低钾能力的差异，并研究了钾的吸收、运转、利用及其机制。两品种在充足供钾(2.5 mmol L^-1)处理下的幼苗干物重相当，但在低钾胁迫下(0.03 mmol L^-1)辽棉18的干物重为新棉99B的2.7倍，表现出较强的耐低钾能力。辽棉18单位根重(或单位根长、单位根表面积)的吸钾量相当或低于新棉99B，叶片钾积累量占整株的比例也显著低于后者，然而其根系发达(根长、根表面积和根体积分别为新棉99B的3.4、3.8和4.2倍)，钾利用指数也较新棉99B高1倍以上。表明辽棉18较强的耐低钾能力与根系生理吸钾能力和钾在植株体内的运转无关，而主要由发达的根系和较高的体内钾利用能力决定。由于低钾条件下辽棉18和新棉99B叶片的渗透势及相对含水量均无显著差异，证明二者体内钾利用能力的不同不在于钾的生物物理功能(调节膨压和渗透势)的高低，而可能主要与钾的生物化学功能(促进光合作用、韧皮部的装载和蛋白质的合成等)有关。

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

Exploiting the 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 Liaomian18 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 potassium (regulation of turgor pressure and osmotic potential), but likely related to the biochemical function of potassium (promotion of photosynthesis, phloem loading and protein synthesis etc.).