Effects of N stress on the physiology of seedlings of Malus hupehensis cultured by hydroponic method

صينى. 以当年生平邑甜茶(Malus hupehensis Rehd．)实生苗为试材，用水培实验方法，研究氮胁迫对其引起的生理效 应。通过8周的处理，对平邑甜茶的功能叶和根系进行相关指标的检测，结果如下：用电导仪进行抗逆性测定，伤害率 由大到小依次为功能叶、吸收根、生长根和木质根。N胁迫影响了功能叶和根系中的N代谢。与MN(midddle N)相比，N胁迫各处理的可溶性蛋白含量均下降。功能叶中游离氨基酸总量表现为HN(high N(low N)MN，而根系中表现为MNHNLN。各器官中，以功能叶和吸收根对N胁迫最为敏感。N胁迫还改变了功能叶和吸收根内的ABA、IAA、ZRs、CA3的含量，从而影响了激素平衡。此外，通过电镜观察可知，N胁迫破坏了叶绿体和吸收根根尖细胞的超微结构。

إنجليزي. A hydroponic experiment was carried out with one-year-old seedlings of Malus hupehensis Rehd. for studying the physiological effects caused by N stress. After 8-week treatment, several correlated indexes were measured in functional leaves and roots, respectively. The results showed that the stress resistances, which determined by conductivity detector, were different in these organs. The order of damage degree from higher to lower was functional leaves, absorbing roots, growing roots and wooden roots. N metabolism was affected by N stress in functional leaves and roots. Compared with MN (middle N), the content of soluble protein decreased in other treatments. The order for free amino acid content was HN(high N)LN(low N)MN in functional leaves, but was MNHNLN in roots. In these organs we detected that functional leaves and absorbing roots were most sensitive to N stress. By use of the electric microscope, it was observed that the ultrastructure of chloroplast of functional leaves and cells of tips of absorbing roots were damaged under N stress. In addition, N stress altered the contents of several kinds of hormones in functional leaves and absorbing roots. The contents of IAA and ZRs in functional leaves enhanced with the N application increasing, but GA3 decreased significantly. ABA content was highest in HN treatment, lowest in MN treatment. In cells of tips of absorbing roots, GA3 content decreased considerably as the N fertilizer rate increasing, and the content of other three hormones were highest in MN treatment. As a result, the balance of hormones changed. The IAA +ZRs +GA3/ABA value of MN treatment was significantly higher than that of LN and HN treatments both in functional leaves and absorbing roots.