The changes of organelle ultrastructure and Ca²⁺ homeostasis in maize mesophyll cells during the process of drought-induced leaf senescence

Yuan-Yuan Ma^1,2 · Xiu-Lin Guo^*1 · Bin-Hui Liu⁵ · Zi-Hui Liu¹ · Hong-Bo Shao*^3,4

¹ Plant Genetic Engineering Center of Hebei Province, Institute of Genetics and Physiology, Hebei Academy of Agricultural and Forestry Sciences, Shijiazhuang, China
² School of Chemical Engineering, Shijiazhuang University, China
³ The CAS / Shandong Provincial Key Laboratory of Coastal Environmental Processes, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China
⁴ Institute for Life Sciences, Qingdao University of Science & Technology, Qingdao 266042, China
⁵ Institue of Dryland Farming, Hebei Academy of Agriculture and Forestry Sciences, Hengshui, China

*Corresponding authors: shaohongbochu@126.com; myhf2002@yahoo.com.cn

Financial support: This work was jointly supported by the Natural Science Foundation of Hebei Province, China (C2007000994), the National Science & Technology Supporting Project, China (2007BAD69B01), the National Natural Science Foundation of China (41001137), The Science & Technology Development Plan of Shandong Province (2010GSF10208), One Hundred-Talent Plan of Chinese Academy of Sciences (CAS), the CAS/SAFEA International Partnership Program for Creative Research Teams, the Important Direction Project of CAS (KZCX2-YW-JC203) and CAS Young Scientists Fellowship (2009Y2B211).

Keywords: Ca²⁺ homeostasis, drought, leaf senescence, maize, organelle ultrastructure, signal transduction.

The changes of cell ultra structure as well as Ca²⁺ homeostasis involved in the drought-induced maize leaf senescence was investigated. Meanwhile, many indicatives of leaf senescence including thiobarbituric acid reactive substance (MDA), electrolyte leakage (EL), and chlorophyll along with soluble proteins were also detected during the process. The Polyethylene glycol6000(PEG6000)-incubated detached leaves showed a slight increase in the MDA content and electrolyte leakage during the first 30 min of our detection, which was corresponded to an unobvious alteration of the cell ultrastructure. Other typical senescence parameters measured in whole leaf exhibited a moderate elevation as well. Thereafter, however, the EL and MDA rose to a large extent, which was correlated with a dramatic damage to the cell ultrastructure with concomitant sharp decrease in the chlorophyll and soluble proteins content. The deposits of calcium antimonite, being an indicator for Ca²⁺ localization, were observed in the vacuoles as well as intercellular spaces in the leaves grown under normal condition. Nevertheless, after PEG treatment, it was revealed a distinct increment of Ca²⁺ in the cytoplasm as well as chloroplasts and nuclei. Moreover, with long-lasting treatment of PEG to the detached leaves, the concentration of Ca²⁺ as described above showed a continuous increment which was consist with the remarked alteration of physiological parameters and severe damage to the ultrastructure of cells, all of which indicated the leaf senescence. Such drought-induced leaf senescence might result from a loss of the cell’s capability to extrude Ca²⁺. All above findings give us a good insight into the important role of Ca²⁺ homeostasis in the process of leaf senescence accelerated by the drought stress.