This study compared physiological and growth responses to water stress of two legume species during the seedling stage. Potted alfalfa (Medicago sativa L. cv. Algonquin) and milkvetch (Astragalus adsurgens Pall. cv. Pengyang earlymaturing vetch) seedlings were grown under well-watered [soil water content (SWC) maintained at 14.92% daily] or water-stressed conditions (drying) for 15 days. Net photosynthetic rate (PN), transpiration rate (E) and stomatal conductance (gs) of both species decreased parabolically. When SWC decreased to 7.2% and 10.3%, gs values for alfalfa and milkvetch were significantly different from those of the respective well-watered plants (p<0.05). When SWC decreased to 6.6% for alfalfa and 6.8% for milkvetch, leaf water potentials (ψL) were significantly different from those of the well-watered plants (p<0.05). Thus the difference between the SWC thresholds for a nonhydraulic root signal (nHRS) and a hydraulic root signal (HRS) were 0.6% and 3.5% for alfalfa and milkvetch, respectively. Milkvetch had a lower gs than alfalfa for a given SWC (p<0.05). Although alfalfa seedlings had a higher dry mass (DM) and root:shoot ratio (R/S) than milkvetch in both treatments (p<0.05), we concluded that milkvetch seedlings had greater drought tolerance than alfalfa. and B.-C. Xu ... [et al.].
Let $r\ge 3$, $n\ge r$ and $\pi =(d_1,d_2,\ldots ,d_n)$ be a non-increasing sequence of nonnegative integers. If $\pi $ has a realization $G$ with vertex set $V(G)=\{v_1,v_2,\ldots ,v_n\}$ such that $d_G(v_i)=d_i$ for $i=1,2,\ldots , n$ and $v_1v_2\cdots v_rv_1$ is a cycle of length $r$ in $G$, then $\pi $ is said to be potentially $C_r''$-graphic. In this paper, we give a characterization for $\pi $ to be potentially $C_r''$-graphic.
The review deals with the comprehensive analysis of ultraviolet-B (UV-B) induced alterations in photosynthetic processes of higher plants and possible protection mechanisms. Between two photosystems, photosystem 2 (PS2) is main target for UV- B radiation stress. Depending on the mode of treatment, the oxidising side of PS2 and reaction centres are mainly affected by UV-B treatment. As response to UV-B stress plants develop some inherent adaptive mechanisms which decide the extent of the overall damage.