Two substances with extended two-dimensional networks through hydrogen-bond cross linkages, namely, [Co(4,4′-bpy)(H2O4] (ClO4)2.(4,4′-bpy)2.2H2O and [Zn(4,4′-bpy)(H2O)3(ClO4)] (ClO4).(4,4′- bpy)1·5.H2O, were synthesized, in EtOH/H2O solution. The cobalt complex crystallizes in the triclinic space group P-1 with a 9·113(2), b 11· 093(2), c 11·394(2) Å, α 64·04(3), β 70·18(3), γ 66·91(3)°, V 932·9(3) Å3. The crystal structure contains 4,4′-bpy-bridged linear polymeric [Co(4,4′-bpy)(H2O)4]n chains, where the cobalt(II) is coordinated in a slightly distorted octahedral environment by four water molecules (Co-O 2·088(2)-2·101(2) Å) at the equatorial positions and two nitrogen atoms of the bridging 4,4′-bpy ligands (Co–N 2·149(2) Å) at the axial positions. The chains are interconnected into a two-dimensional rhombic network by double hydrogen-bond bridges of the type Co–H2O · · · bpy · · · H2O–Co. The zinc complex also crystallizes in the triclinic space group P-1 with a 9·0230(11), b 11·299(2), c 16·397(2) Å, α 74·429(11), β 83·132(9), γ 70·654(12)°, V 1518·5(3) Å3. The crystal structure contains 4,4′-bpy-bridged linear polymeric [Zn(4,4′-bpy)(H2O)3(ClO4)]n chains, where the zinc atom is coordinated in a distorted octahedral environment by two nitrogen atoms of the bridging 4,4′-bpy ligands (Z–N 2·104(2)–2·117(2) Å), three water molecules (Zn–O 2·068(2)–2·091(2) Å) and one monodentate ClO4- anion (Zn–O 2·320(2) Å). The chains are interconnected into a rhombic network alternately by single or double hydrogen-bond bridges of the type Zn–H2O · · · 4,4′-bpy · · · H2O–Zn.

For galling aphids and their hosts, tannins are crucial for plant-insect interactions and for protecting the host plant from herbivory. Due to their peculiar chemical characteristics, tannins from plant galls have been used for medical and chemical purposes for more than 2000 years. In this study, hydrolyzable tannin concentrations in galls increased from gall initiation (38.34% on June 21) to maturation (74.79% on August 8), then decreased gradually thereafter (58.83% on October 12). We identified a total of 81 genes (named as GTS1-81) with putative roles in gallotannin biosynthesis and 22 genes (TS1-22) in condensed tannin biosynthesis. We determined the expression profiles of these genes by real-time PCR over the course of gall development. Multiple genes encoding 1-beta-D-glucosyl transferases were identified, which may play a vital role in gallotannin accumulation in plant galls. This study is the first attempt to examine the molecular basis for the regulation of tannin accumulation in insect gallnuts. The differentially expressed genes we identified may play important roles in both tannin biosynthesis and plant-insect interactions.

It has been a long-standing question as to whether the interaction between gall-forming insects and their host plants is merely parasitic or whether it may also benefit the host. On its host Rhus chinensis, the aphid Schlechtendalia chinensis induces the formation of closed galls, referred to as horned galls. Typically, mature aphid populations comprise thousands of individuals, which is sufficient to cause the accumulation of high CO₂ levels in galls (on average 8-fold higher and up to 16 times than atmospheric levels). Large aphid populations also excrete significant amounts of honeydew, a waste product high in sugars. Based on ¹³C isotope tracing and genomic analyses, we showed that aphid-derived carbon found in CO₂ and honeydew was recycled in gall tissues via photosynthesis and glycometabolism. These results indicated that the aphid-gall system evolved in a manner that allowed nutrient recycling, where the gall provides nutrients to the growing aphid population, and in turn, aphid-derived carbon metabolites provide a resource for the growth of the gall. The metabolic efficiency of this self-circulating system indicates that the input needed from the host plant to maintain aphid population growth less than previously thought and possibly minimal. Aside from the recycling of nutrients, we also found that gall metabolites were transported to other parts of the host plant and is particularly beneficial for leaves growing adjacent to the gall. Taken together, galls in the S. chinensis–Rhus chinensis system are highly specialized structures that serve as a metabolic and nutrient exchange hub that benefits both the aphid and its host plant. As such, host plants provide both shelter and nutrients to protect and sustain aphid populations, and in return, aphid-derived metabolites are channeled back to the host plant and thus provide a certain degree of “metabolic compensation” for their caloric and structural needs.