Zephyranthes tubispatha is an ornamental species distributed along several countries of South America. Although it can be multiplied through bulbs or scales, seed germination is a simpler and more cost-effective process. Temperature plays a major role in the control of germination; however, its effect has been scarcely investigated in this species. In the present work, we characterized the germination responses of Z. tubispatha seeds to different temperatures and analyzed the role of key components of the antioxidant metabolism and phytohormones in their control. Seeds showed an optimal temperature range for germination between 14 and 20°C, with higher temperatures (HTs) being progressively inhibitory. While germination was almost nil above 28°C, it could be recovered after transferring the seeds to 20°C, suggesting that thermoinhibition was the underlying phenomenon. The duration of the HT incubation period affected both the time to germination onset and the germination rate at 20°C. Similarly, the activity of antioxidant enzymes, the production of reactive oxygen species in the embryo and the sensitivity to some germination promoters varied depending on the duration of the HT treatment. The addition of 20 μM fluridone was sufficient to recover germination dynamics as in the control treatment when given after a long-term incubation period (25 d) at HT. Ethephon supply was more effective than gibberellins to suppress thermoinhibition, suggesting that changes in the balance and/or sensitivity to ethylene and abscisic acid over time play an important role in the regulation of germination responses to thermal cues in this species.

Seed germination, the first and critical step of the plant's life cycle, is affected by salt stress. However, the underlying mechanism of salt tolerance during early seed germination remains elusive. Here, a comparative RNA-seq analysis was performed using early germinating seeds either under normal conditions or in 100 and 150 mM sodium chloride. A total of 575 genes were up-regulated and 913 genes were down-regulated in the presence of 100 mM NaCl. Under the 150 mM NaCl treatment 1921 genes were up-regulated and 3501 genes were down-regulated. A total of 379 or 863 genes were up-regulated or down-regulated in both 100 and 150mM NaCl. These co-regulated genes were further analysed by GO enrichment. Genes in the categories abscisic acid signaling and synthesis and nutrient reservoir activity were significantly enriched in the up-regulated genes. Transcription factors responsive to gibberellin and auxin were significantly down-regulated by salinity stress. Genes related to anti-oxidant activity were significantly enriched in the down-regulated gene clusters by NaCl treatment. Our results suggest that salt stress inhibits seed germination by activating ABA synthesis and signalling, and depressing GA and auxin signalling, while preserving nutrition and down-regulated anti-oxidant activity. Our study provides more insight into the molecular mechanism of salt tolerance during early seed germination.

Japanese knotweed is an aggressive alien species in Europe, North America, and Australia, causing a range of environmental problems. Eradication of Japanese knotweed is proving to be a difficult task, because the plant is able to propagate generatively by intra- and interspecific hybridization, and vegetatively from shoot and tiny rhizome pieces. Despite the economic consequences of Japanese knotweed on natural and built environments, its physiology is not yet fully understood; especially important are sink-source relations between old and young parts of the rhizome and growth of lateral and latent rhizome buds. Current methods of chemical control include three types of phloem-mobile herbicides, such as glyphosate, imazapyr, and synthetic auxins. These herbicides have limitations on their use, and all fail to eradicate the plant completely, for the reasons discussed in this review. Our aim is to suggest prospective approaches to enable chemical eradication: use of signals to induce controlled growth and development of quiescent rhizome buds; use of phytohormones, sugars, and light to increase allocation of phloem-mobile herbicides to the rhizome; use of xylem-mobile herbicides to exterminate the old rhizome parts; and use of different phloem-mobile herbicides at different growth stages.

Recommended rates of glyphosate for noncultivated areas destroy theaboveground shoots of the perennial plant leafy spurge. However, suchapplications cause little or no damage to underground adventitious buds(UABs), and thus the plant readily regenerates vegetatively. Highconcentrations of glyphosate, applied under controlled environmentalconditions, have been shown to cause sublethal effects in UABs of leafyspurge that produce stunted and bushy phenotypes in subsequent generationsof shoots. We treated leafy spurge plants in the field with glyphosate (0,1.1, 3.4, or 6.7 kg ai ha−1) to determine its effects onvegetative growth from UABs and on molecular processes. The number of shootsderived from UABs of glyphosate-treated plants was significantly increasedcompared to controls in subsequent years after application, and new shootsdisplayed various phenotypical changes, such as stunted and bushyphenotypes. Quantifying the abundance of a selected set of transcripts inUABs of nontreated vs. treated plants (0 vs. 6.7 kg ha−1)indicated that glyphosate impacted molecular processes involved inbiosynthesis or signaling of tryptophan or auxin (ARF4, CYP79B2, PIN3, TAA1, TRP6, YUC4), gibberellic acid (GA1/CPS1, GA2/KS), ethylene (ACO1, ACS10), cytokinins (AHP1, AK2, CKX1), andthe cell cycle (CDC2A, CDC2B, CYCD3;1). Glyphosate-induced effects on vegetativegrowth and transcript abundance were persistent for at least 2 yr aftertreatment. Determining the molecular mechanisms associated with vegetativereproduction in leafy spurge following foliar glyphosate-treatment couldidentify limiting factors or new targets for manipulation of plant growthand development in perennial weeds.

The most critical phase in plant life is seed germination, which is influenced by environmental factors. Drought and salinity are key environmental factors that affect seed germination. Reduction or alterations of germination when seeds are exposed to these factors have been shown to be due to either the adverse effects of water limitation and/or specific ion toxicity on metabolism. Phytohormones are chemical messengers produced within the plant that control its growth and development in response to environmental cues; small fluctuations of phytohormone levels alter the cellular dynamics and, hence, play a central role in regulating plant growth responses to these environmental factors. To integrate current knowledge, the present review focuses on the involvement of endogenous phytohormones in plant adaptative responses to drought and salinity at one of the plant's developmental phases.

It has been demonstrated that the surface lipophilicity of the plant-parasitic nematode Globodera rostochiensis decreases when infective larvae are exposed to the phytohormones indole-3-acetic acid (auxin) or kinetin (cytokinin). In the present study, it was shown that inhibition of phospholipase C (PLC) or phosphatidylinositol 3 kinase (PI3-kinase) reversed the effect of phytohormones on surface lipophilicity. The signalling pathway(s) involved in surface modification were investigated using ‘caged’ signalling molecules and stimulators or inhibitors of different signalling enzymes. Photolysis of the ‘caged’ signalling molecules, NPE-caged Ins 1,4,5-P3, NITR-5/AM or caged-cAMP to liberate IP3, Ca2+ or cAMP respectively, decreased the surface lipophilicity. Activation of adenylate cyclase also decreased the surface lipophilicity. In contrast, inhibition of PI3-kinase using Wortmannin, LY-294002 or Quercetin, and inhibition of PLC using U-73122 all increased the surface lipophilicity. Two possible signalling pathways involved in phytohormone-induced surface modification are proposed.

Roots of Lablab purpureus (L.) Sweet were treated with tri-iodobenzoic acid (TIBA), kinetin or with nodulation factors (Nod factors) purified from Rhizobium sp. NGR234 and grown in the presence of a mycorrhizal inoculum (Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe. Colonization by the mycorrhizal fungus was increased from <30% to c. 65% of root length when roots were treated with these growth regulators. Moreover, treatment of mycorrhizal L. purpureus roots with Nod factors or TIBA strongly induced sporocarp formation of Glomus mosseae. In parallel, the pool size of the fungal disaccharide trehalose was significantly affected in roots treated with TIBA and Nod factors alone, and with TIBA combined with all effectors, and increased from 0·06 mg g−1 d. wt in control roots to up to 1·7 mg g−1 d. wt (TIBA+kinetin). Conversely, the sucrose pool decreased from 5% d. wt to less than a half in roots treated with Nod factors. Activities of trehalase were significantly enhanced in mycorrhizal roots by the treatment with Nod factors or TIBA. When Nod factors and TIBA were added in combination, these activities were strongly enhanced suggesting synergism between these growth regulators.