Physiological Integration And Its Regulation Between Inter-ramet Of Buffalograss Under Heterogeneous Water Stress

Physiological integration, the bility to transport resources (photosynthates, nutrients, and other materials) between ramets of clonal plants through these connections, such as rhizome and stolon, improve their ability to cope with habitat heterogeneity, and is a property of many rhizomatous and stoloniferous clonal plant species. Clonal plants have been shown advantage in survival, propagation and resource utilizations under heterogeneous environment. And play a critical important role in Ecological Restoration. Up to date, whereas the patterns of resource sharing in great many species of clonal plants are well documented, the mechanism for physiological integration has been little explored.In this paper, to prove the existence of physiological integration, we studied translocation patterns of water and photosynthesis assimilation between inter-connected ramets of Buchloe dactyloides (Nutt.) Engelm.'Texoka'by using acid fuchsin and 14C isotopic tracing under heterogeneous water stress. Proteins responding to heterogeneous water stress in the leaves of buffalograss were also studied using proteomics technique combination with determination of physiological metabolism based on the research result metioned above. The results were shown as follow.(1) Resources in clonal plants are share and retribution among the interconnected ramets according to source-sink relationships under heterogeneous environments. The higher number was attributed to the significant increase in the sand with well watering medium and sand with water deficiency medium as compared to those in the homogeneous environments, and the mount of ramet in peat with well watering medium were also slight increasing than those under homogeneous environment, indicating that the offspring ramets under unfavorable conditions were benefiting from physiological integrations.(2) Water transport is predominantly acropetal within the ramets, while acxropetal, basipetal and bidirectional transport of water between connected-3-ramet clonal fragments of buffalograss can be found under heterogeneous water condition. And the degree and extension of transport differ according the water potential within the single ramet and among the ramets.(3) The directions of 14C-labeling were predominantly acropetal among the ramets in either homogenous or heterogeneous water stress environment. When the younger ramet suffered from water stress, the mount of photosynthates imported to the younger one from the old ramet increase evidently. And the old one suffering from water stress was also obtain increasing photosynthates from its neighboring younger ramet. However, the output rate of the 14C-labeling from the labeled ramet was not higher than 19.78%. The result indicated that photothates can be shared among the ramets responding to the heterogeneous water stress, although the degree of physiological integration is very limited.(4) ABA content increased evidently when one ramet suffered from water stress under heterogeneous water stress, and the assimilation of ABA in the ramet under water stress with PEG-6000 is much faster than other ramet in the same clonal fragment of buffalograss. However, IAA content in the connected ramets has dramatic reduce when anyone of the clonal fragment was suffered from water stress. The concentration of GAs and ZR decreased with different degree when one ramet cultured in water stress environment. Those indicate that endogenous hormones, especially IAA and ABA may play critical important roles in regulation of physiological integration.(5) Production rate of superoxide anion radical (O2-.) and contents of Hydrogen Peroxide (H2O2) and Malondialdehyde (MDA) increasing with the degree of water stress enhanced gradually. 24 h to 60 h after the single ramet cultured in the heterogeneous water stress, the production rate of O2-. and accumulations of H2O2 and MDA showed increased in line. And the activities of Superoxide dismutase (SOD), Guaiacol peroxidase (G-POD) and Catalase (CAT) show the trend of rise first then fall. The time of the peak value of antioxidant enzymes mentioned above advanced with the degree of water stress increased.(6) The activity of SOD and G-POD in the leaves of inter-ramets rose gradually and reach to the maximums later (at 60 h after anyone of them cultured in water stress conditions with 20% PEG-6000 comparison to those of single ramet under water stress. Content of MDA and free proline (Pro) in the leaves of inter-ramets under heterogeneous water stress and single ramet under water stress increased gradually with time going comparison to the control. However, the accumulation of MDA and Pro in the single ramet under water stress much higher and faster than those of the connected ramets. The result showed that the resistance to oxidative stress caused by heterogeneous water stress in the pairs of ramets is also significantly elevated base on physiological integration among connected ramets of buffalograss.(7) A total of 44 different proteins changed significantly were indentified after the inter-ramets cultured in heterogeneous water stress for 48 h comparison to the control ramet. These identified proteins are involved in photosynthesis (9%), lipid metabolism (4%), carbonhydrate metabolism (4%) energy metabolism (9%), protein processing (7%) , transcription (9%), stress response (7%), signal transduction (9%) and others according to their physiological function in the growth and development of plant. The proteins different expressed in the leave of connected ramet intact were identified comparison to the control. These proteins can also be divided into several classes, such as Ribulose-1, 5-bisphosphate carboxylase/oxygenase large subunit involvement in photosynthesis, Putative cinnamoyl CoA and Sucrose synthase type 2 involved in metabolism of lipid and carbohydrate and Heat shock protein 70 involvement in stress response. The proteins expressed significant changed in the leaves of connected ramet under water stress with 20% PEG-6000 were involved to several categories, such as Ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (photosynthesis), Phytochrome A (signal transduction), ATP synthase subunit alpha, chloroplastic and Atpase alpha subunit, 3'-partial (energy metabolism), Putative cinnamoyl CoA (lipid metabolism), ACC Oxidase (stress response), and Dynamin-related protein 12A (cell growth and division).In conclusion, heterogeneous water stress can be percept by connected clonal ramet of buffalograss. Endogeneous hormones, antioxidant enzymes and functional proteins different expressed play critical important roles in regulation of physiological integration of water and photosynthates among inter-ramet resulting in the modification of clonal growth pattern for adaptability of heterogeneous envirnments.