不同硼效率棉花品种木质部和韧皮部汁液中矿质养分的差异

溶液培养条件下研究硼对2个硼效率不同的棉花品种木质部、韧皮部中硼及其它矿质养分运输的影响。结果表明,缺硼使2个棉花品种木质部汁液硼含量及溢出量明显降低,低效品种降低幅度大于高效品种。供硼充足(0.5mg/L)时,2个棉花品种木质部汁液中硼浓度均小于培养液中硼浓度;缺硼(0.002mg/L)时,高效品种与低效品种木质部汁液硼浓度分别是培养液硼浓度的32.0和20.5倍。缺硼使2个棉花品种木质部汁液中钾、锰、铜、锌含量均升高,高效品种升高幅度较大;钙含量均降低,低效品种降低幅度较大;高效品种镁含量增高,低效品种降低。而2个棉花品种木质部各养分(钾、镁、钙、锰、铜、锌)溢出量均降低,低效品种降低更明显。无论在缺硼或供硼充足时,2个棉花品种韧皮部中硼浓度均极低,但韧皮部溢泌液中其它养分受缺硼影响品种间表现不同,高效品种韧皮部钾、镁、锰、铜溢出量升高,低效品种则降低;2个品种钙、锌溢出量均降低,低效品种降低幅度更大。

Differences in mineral nutrients content in xylem and phloem sap between cotton cultivars with different boron efficiency

Boron deficiency is one of the most widespread of all micronutrient deficiencies. Plant response to boron deficiency varies widely among species or genotypes. In our past experiment, the differences were observed in boron content in shoots and distribution in different organs between B-efficient cultivar "9901" and B-inefficient one "9903". It has been proved that the phenomenon was in connection with different capacity of boron uptake between two cotton cultivars under boron deficiency. Bellaloui et al (1998) and Takano et al (2002) reported genotypic differences of boron efficiency in some species was attributed to different boron transport from roots to shoots. To further elucidate the mechanism of cotton genotypic differences, the transport of B and other mineral nutrients in xylem and phloem in two cotton cultivars with different B efficiency was studied under boron deficiency. The cotton seedlings were cultured in Hoagland solution, the 5-leaf-old seedlings were treated by 3 boron levels: 0, 0.002, 0.50 mg B per liter. The phloem and xylem exudation sap was collected after two weeks and the content of some mineral nutrients in the sap was determined by ICP-OES. Almost no boron was detected in cotton phloem sap at sufficient or insufficient boron supply, suggesting that B mobility in cotton was restricted. Boron concentration and exudation rate in xylem sap of two cotton cultivars were decreased at boron deficiency, but the trend was more obvious in B-inefficient cultivar. The B concentration in xylem sap of both cotton cultivars was lower than that of nutrient solution under sufficient boron supply (0.5 mg/L), but the contrary trend was found at a lower B supply (0.002 mg/L). B concentration in xylem sap for the efficient cultivar was up to 32 fold higher than in the nutrient solution and compared to 20.5 fold for the inefficient one. These suggest that there may be two different mechanisms for B translocation into xylem: a passive diffusion process plays an important role at sufficient B supply, but a concentration mechanism is involved at low B concentration. It seems that the latter mechanism works in B efficient (cotton) cultivar. The content of K, Mn, Cu and Zn in xylem sap in two cotton cultivars was increased at B deficiency, (but) with greater intensity in B efficient cultivar. The exudation rate of K, Mg, Ca, Mn, Cu and Zn in xylem sap of both (cotton) cultivars was cut down at B deficiency, the degree of reduction in B inefficient cultivar being greater than in B (efficient) one. When B was extremely insufficient, the exudation rate of K, Mg, Mn and Cu in phloem sap of B efficient (cotton) cultivar was raised, but depressed in B inefficient one. The exudation rate of Ca and Zn in phloem sap of both (cultivars) was decreased, but to greater degree in B inefficient one.