Photosynthate integration and regulation within clones of buffalograss under heterogeneous water supply

Physiological integration(translocation of resources) in clonal plants can improve their ability to cope with heterogeneous environments.Photosynthate integration may increases when one part of a clonal fragment(clone) is subjected to environmental stress such as drought and shading.However,few studies have examined mechanisms underlying physiological integration in clonal plants.The objective of this study was to examine the effects of water stress on the allocation patterns of endogenous hormones(ABA and IAA) and photosynthates within clones of the stoloniferous grass Buchloe dactyloides(buffalograss).We measured abundance of 14C-lableled photosynthates and concentrations of ABA and IAA in clonal fragments of buffalograss under homogeneous and heterogeneous water supply.Each clonal fragment consisted of three ramets,i.e.a relatively old,young and intermediate aged ramet.In the homogeneous treatments all three ramets of the fragments were grown without water stress and one ramet was labeled with 14C.In the heterogeneous treatments one ramet of the clonal fragments was subjected to water stress by 30% PEG-6000 and the other two were not,and one ramet was also labeled with 14 C.14 C-photosynthate translocations were predominantly acropetal,i.e.from the older to the younger ramets.Import of 14 C-photosynthates to the neighbor ramet was larger when the neighbor ramet was suffering from water stress(heterogeneous treatments) than when it was not(homogeneous treatments).On the other hand,export of 14C-photosynthates from the ramet subjected to water stress(heterogeneous treatments) decreased significantly as compared with the ramet not subjected to water stress(homogeneous treatments).As compared with the homogeneous treatments,IAA contents in all the three ramets of the clonal fragments decreased under heterogeneous water treatments,whereas ABA contents and ABA/IAA increased.The results suggest that heterogeneous water supply can affect the carbohydrate integration among connected ramets of buffalograss,and that the stressed ramet can benefit greatly from its connected unstressed ramet.Because plant hormones play important roles in regulating developmental processes,signaling networks involved in plant responses to a wide range of biotic and abiotic stresses and balance of sink-source relationship,the changes in ABA and IAA in response to heterogeneous water supply suggest that endogenous hormones such as ABA and IAA may play an important role in controlling physiological integration of carbohydrates within connected ramets.