Effects of Different Exogenous Substances on Seed Germination of Isatis indigotica Under Drought Stress and Chemical Composition of Isatis indigotica leaves

This study was to investigate the effects of three exogenous substances on chemical constituents of Isatis indigotica leavesand their efficacy in alleviating drought stress, and explore the methods of applying exogenous substances to efficient cultivationof Isatis indigotica. Polyethylene glycol (PEG) was used to simulate drought stress to deal with seeds of Isatis indigotica at thegermination stage (concentration: 0, 10%, 15%, and 20%). Simultaneous operation of exogenous growth regulators [microbialinoculum (MI), γ-aminobutyric acid (GABA) and salicylic acid (SA)] and PEG were implemented in seeds of Isatis indigotica.The effects of drought stress and the mitigation of exogenous substances were observed by statistics of seed germination potential,germination rate, hypocotyl length, and radicle length of each treatment. The effects of exogenous substances on the content ofalkaloids, crude protein and free amino acids in the leaves of Isatis indigotica grown in a greenhouse were determined after sprayingexogenous substances on the plants. The differences of germination potential, germination rate, hypocotyl length, and radicle lengthamong 15% PEG stress treatment, 10% PEG stress treatment and the control were significant (P<0.05). According to the predesignedgermination standard, the seeds did not germinate under 20% PEG stress treatment. When the PEG concentration was 15%, the resultsof seed germination potential and germination rate after adding MI were significantly different from those under stress alone (P<0.05).When exposed to 10% PEG stress, the supplementation of GABA led to a notable increase in radicle length of Isatis indigotica seeds,showing significant differences compared to other three treatments. The application of MI and GABA under 15% PEG stress resultedin a significant increase in the radicle and hypocotyl length of Isatis indigotica seeds compared to other two treatments. The contentof the total alkaloids in leaves of Isatis indigotica was significantly increased after spraying GABA. Meanwhile, the contents of crudeprotein and the total free amino acids were kept constant after spraying exogenous substances. Application of MI and GABA couldalleviate drought stress of Isatis indigotica. The content of the total alkaloids in leaves of Isatis indigotica could significantly increaseafter spraying GABA.

Molecular mechanism of mureidomycin biosynthesis activated by introduction of an exogenous regulatory gene ssa A into Streptomyces roseosporus

Mureidomycins(MRDs), a group of unique uridyl-peptide antibiotics, exhibit antibacterial activity against the highly refractory pathogen Pseudomonas aeruginosa. Our previous study showed that the cryptic MRD biosynthetic gene cluster(BGC) mrd in Streptomyces roseosporus NRRL 15998 could not be activated by its endogenous regulator 02995 but activated by an exogenous activator Ssa A from sansanmycin’s BGC ssa of Streptomyces sp. strain SS. Here we report the molecular mechanism for this inexplicable regulation. EMSAs and footprinting experiments revealed that Ssa A could directly bind to a 14-nt palindrome sequence of 5′-CTGRCNNNNGTCAG-3′ within six promoter regions of mrd. Disruption of three representative target genes(SSGG-02981, SSGG-02987 and SSGG-02994) showed that the target genes directly controlled by Ssa Awere essential for MRD production. The regulatory function was further investigated by replacing six regions of SSGG-02995 with those of ssa A.Surprisingly, only the replacement of 343–450 nt fragment encoding the 115–150 amino acids(AA) of Ssa A could activate MRD biosynthesis. Further bioinformatics analysis showed that the 115–150 AA situated between two conserved domains of Ssa A.Our findings significantly demonstrate that constitutive expression of a homologous exogenous regulatory gene is an effective strategy to awaken cryptic biosynthetic pathways in Streptomyces.

Review on Effects of Application of Exogenous Growth Regulating Substance on Fruits Weight of Peach

The effects of exogenous growth regulating substance on the fruit weight of peach were reviewed. Paclobutrazol could increase the single fruit weight in dif- ferent degree, and cytokinins could also increase the single fruit weight. GA3 and B9 had no effect on fruit size or on reducing single fruit weight. Chlorflurenol-methy, ABT and salicylic acid had no effect on fruit size. Suggestions on the future re- search were put forward.

Effects of Different Treatments on Seed Germination of Bupleurum chinensis

In order to solve the problem of low emergence rate of Bupleurum chinense seeds, and screen out the best germination conditions, the seeds of Bupleurum chinense L. were treated with different soaking time, germination temperature and exogenous regulating substances to improve the germination rate. The results showed that the germination rate of fresh water at 12 h was significantly higher than that at 8 h and 36 h; The germination rate of seeds treated with constant temperature 15℃ and variable temperature 25 ℃/15 ℃ （day/night） was significantly higher than that of other temperature treatments. Seed soaking time and culture temperature also influenced seed germination start day and peak day. Different concentrations of regulatory substances could promote seeds germination. The germination rate of seeds induced by 0.50 mg/L 6-BA was the highest, the start day and peak day were 4 days and 5 days earlier than control check （CK） respectively.

Improving crop drought resistance with plant growth regulators and rhizobacteria: Mechanisms, applications, and perspectives

Drought is one of the main abiotic stresses that cause crop yield loss.Improving crop yield under drought stress is a major goal of crop breeding,as it is critical to food security.The mechanism of plant drought resistance has been well studied,and diverse drought resistance genes have been identified in recent years,but transferring this knowledge from the laboratory to field production remains a significant challenge.Recently,some new strategies have become research frontiers owing to their advantages of low cost,convenience,strong field operability,and/or environmental friendliness.Exogenous plant growth regulator(PGR)treatment and microbe-based plant biotechnology have been used to effectively improve crop drought tolerance and preserve yield under drought stress.However,our understanding of the mechanisms by which PGRs regulate plant drought resistance and of plant-microbiome interactions under drought is still incomplete.In this review,we summarize these two strategies reported in recent studies,focusing on the mechanisms by which these exogenous treatments regulate crop drought resistance.Finally,future challenges and directions in crop drought resistance breeding are discussed.