No abstract

Glycinebetaine (GB) and humic acid (HA) are 2 commercial growth regulators that are being used worldwide to enhance the tolerance of most crops, including fruit trees, to various stresses, including drought stress (DS). Malus robusta Rehder is considered as one of the most important rootstocks for apple in China, but its growth and productivity is believed to be adversely affected by DS. The effects of different concentrations and combinations of GB (0, 100, and 200 mg L -1 ) and HA (0, 500, 1000, and 1500 mg L -1 ) on M. robusta seedling growth, photosynthesis characteristics, osmolyte accumulation, and antioxidant responses were evaluated under DS and non-DS conditions. GB and HA applied exogenously to drought-stressed M. robusta seedlings increased total dry matter, net photosynthetic rate, free proline content, endogenous glycinebetaine content, soluble sugar content, and potassium content as well as the activities of superoxide dismutase, peroxidase, and catalase. However, GB and HA decreased stomatal conductance and malondialdehyde content. The above-mentioned responses were greater for combined application of GB and HA as compared to application of only GB or HA. The best responses for most of the above parameters were with the application of 100 mg L -1 GB and 1500 mg L -1 HA. These results suggest that application of GB and HA could mitigate the deleterious effects of DS on Malus seedlings and offer an efficient, economical, and simple means to enhance DS tolerance of the apple rootstock.

We present a directed essential dynamics (DED) method for peptide and protein folding. DED is a molecular dynamics method based on the essential dynamics sampling and the principal component analysis. The main idea of DED is to use principal component analysis to determine the direction of the most active collective motion of peptides at short intervals of time (20 fs) during the folding process and then add an additional force along it to adjust the folding direction. This method can make the peptides avoid being trapped in the local minima for a long time and enhance the sampling efficiency in conformational space during the simulation. An S-peptide with 15 amino acids is used to demonstrate the DED method. The results show that DED can lead the S-peptide to fold quickly into the native state, whereas traditional molecular dynamics needs more time to do this.

Drought is a major environmental stress that limits the growth and productivity of fruit trees in semiarid and arid regions. We evaluated the potential of exogenous nitric oxide (NO) to improve the drought tolerance of apple rootstocks (Malus spp.). Leaves of 2-year-old seedlings of drought-sensitive Malus hupehensis (Pamp.) Rehd. and drought-tolerant Malus sieversii (Ledeb.) M.Roem. rootstocks were sprayed with NO donor sodium nitroprusside (SNP) at 0-400 µmol L-1 , and then the plants were subjected to drought stress. Among all SNP treatments, the 300 µmol L-1 SNP treatment mostly alleviated drought-induced ion leakage and the accumulation of malondialdehyde and soluble proteins in M. sieversii and M. hupehensis leaves. These changes helped to maintain leaf water potential and relative water content of the apple rootstocks under drought stress. The activities of several antioxidant enzymes in leaves increased under drought stress, whereas photochemical efficiency decreased. The adverse effects of drought were exacerbated by treatment with the NO scavenger cPTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt; 400 µmol L-1); however, this effect was offset by NO application. These results suggested that the NO donor SNP effectively protected Malus seedlings from droughtinduced oxidative damage by enhancing antioxidant enzyme activities and photosynthetic performance.