Zhou Yanhong, Huang Lifeng, Zhang Yili, Shi Kai, Yu Jingquan, Nogués Salvador
Department of Horticulture, Huajiachi Campus, Zhejiang University, Kaixuan Road 268, Hangzhou, PR China 310029.
Ann Bot. 2007 Oct;100(4):839-48. doi: 10.1093/aob/mcm181. Epub 2007 Aug 29.
Chilling results in a significant decrease in Rubisco content and increased generation of reactive oxygen species (ROS) in cucumber (Cucumis sativus), a chilling-sensitive species. The role of roots in the regulation of the tolerance is unknown. Here, cucumber plants grafted onto figleaf gourd (Cucurbita ficifolia), a chilling-tolerant species were used to study the role of roots in the regulation of shoot functioning and the associated root-to-shoot communication.
Gas exchange and chlorophyll fluorescence were measured using an infrared gas analyser combined with a pulse amplitude fluorimeter during chilling at 14 degrees C or 7 degrees C and subsequent recovery. At the same time, Rubisco content and activity and ROS generation were spectrophotometrically assayed. Abscisic acid and cytokinin concentrations in xylem sap were also determined by enzyme-linked immunosorbent assay.
Grafted plants showed a significantly higher light-saturated rate of CO(2) assimilation (A(sat)) than own-rooted plants when roots were gradually cooled, but no differences were detected when shoots were cooled. Chill at 7 degrees C irreversibly reduced A(sat), and significantly decreased maximum carboxylation activity, Rubisco content and initial Rubisco activity. However, grafted plants showed weaker inhibition, together with decreased electron flux in the water-water cycle. Higher activity of antioxidant enzymes with less ROS production was found in grafted plants. In addition, ABA concentration increased by 48.4-fold whilst cytokinin concentration decreased by 91.5% in the xylem sap of own-rooted plants after exposure to a 7 degrees C chill. In comparison, ABA and cytokinin concentrations increased by 10.5-fold and 36.9%, respectively, for the grafted plants. Improved plant growth was also observed in grafted plants after the chill. These results suggest that some signals coming from chilling-resistant roots (i.e. ABA and cytokinins) protect leaf photosynthesis in shoots of chilling-sensitive plants.
低温导致冷敏感植物黄瓜（Cucumis sativus）中核酮糖-1,5-二磷酸羧化酶（Rubisco）含量显著降低，并增加活性氧（ROS）的生成。根系在调节耐受性中的作用尚不清楚。在此，将黄瓜植株嫁接到耐冷物种黑籽南瓜（Cucurbita ficifolia）上，以研究根系在调节地上部功能及相关根-冠通讯中的作用。
在14℃或7℃低温处理及随后的恢复过程中，使用红外气体分析仪结合脉冲幅度荧光计测量气体交换和叶绿素荧光。同时，采用分光光度法测定Rubisco含量、活性及ROS生成。还通过酶联免疫吸附测定法测定木质部汁液中脱落酸和细胞分裂素的浓度。
当根系逐渐冷却时，嫁接植株的二氧化碳同化光饱和速率（A(sat)）显著高于自根植株，但地上部冷却时未检测到差异。7℃低温不可逆地降低了A(sat)，并显著降低了最大羧化活性、Rubisco含量和初始Rubisco活性。然而，嫁接植株的抑制作用较弱，同时水-水循环中的电子通量降低。嫁接植株中抗氧化酶活性较高，ROS生成较少。此外，自根植株在7℃低温处理后，木质部汁液中脱落酸浓度增加了48.4倍，而细胞分裂素浓度降低了91.5%。相比之下，嫁接植株的脱落酸和细胞分裂素浓度分别增加了10.5倍和36.9%。低温处理后，嫁接植株的生长也有所改善。这些结果表明，来自抗冷根系的一些信号（即脱落酸和细胞分裂素）保护了冷敏感植物地上部叶片的光合作用。
