A dominating set in a graph $G$ is a connected dominating set of $G$ if it induces a connected subgraph of $G$. The minimum number of vertices in a connected dominating set of $G$ is called the connected domination number of $G$, and is denoted by $\gamma _{c}(G)$. Let $G$ be a spanning subgraph of $K_{s,s}$ and let $H$ be the complement of $G$ relative to $K_{s,s}$; that is, $K_{s,s}=G\oplus H$ is a factorization of $K_{s,s}$. The graph $G$ is $k$-$\gamma _{c}$-critical relative to $K_{s,s}$ if $\gamma _{c}(G)=k$ and $\gamma _{c}(G+e)<k$ for each edge $e\in E(H)$. First, we discuss some classes of graphs whether they are $\gamma _{c}$-critical relative to $K_{s,s}$. Then we study $k$-$\gamma _{c}$-critical graphs relative to $K_{s,s}$ for small values of $k$. In particular, we characterize the $3$-$\gamma _{c}$-critical and $4$-$\gamma _{c}$-critical graphs.
Photosynthetic responses of potato (Solanum tuberosum L. cv. Chunzao) were examined during potato virus Y (PVYNTN) infection. PVYNTN infection significantly reduced net photosynthetic rate and stomatal conductance, but had little influence on intercellular CO2 concentration. As the disease developed, the maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the maximum electron transport rate contributing to ribulose-1,5-bisphosphate regeneration gradually decreased, followed by substantial reductions in the relative quantum efficiency of photosystem 2 (PS2) electron transport, the efficiency of excitation energy capture by open PS2 reaction centres, and photochemical quenching, but not in sustained photoinhibition. Thus PVYNTN depressed photosynthesis mainly by interfering with the enzymatic processes in the Calvin cycle which resulted in a down-regulation of electron transport. and Y. H. Zhou ... [et al.].