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ABSTRACT Depending on geographical location, plants are exposed to variable amounts of UVB radiation and herbivore attack. Because the role(s) of UVB in the priming and/or accumulation of plant defence metabolites against herbivores are not well understood, we used field-grown Nicotiana attenuata plants to explore the effects of UVB on herbivore performance. Consistent with previous reports, UVB-exposed plants accumulated higher levels of ultraviolet (UV)-absorbing compounds (rutin, chlorogenic acid, crypto-chlorogenic acid and dicaffeoylspermidine). Furthermore, UVB increased the accumulation of jasmonic acid, jasmonoyl-L-isoleucine and abscisic acid, all phytohormones which regulate plant defence against biotic and abiotic stress. In herbivore bioassays, N. attenuata plants experimentally protected from UVB were more infested by mirids in three consecutive field seasons. Among defence metabolites measured, 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) showed strongly altered accumulation patterns. While constitutive HGL-DTGs levels were higher under UVB, N. attenuata plants exposed to mirid bugs ( Tupiocoris notatus) had still more HGL-DTGs under UVB, and mirids preferred to feed on HGL-DTGs-silenced plants when other UVB protecting factors were eliminated by UVB filters. We conclude that UVB exposure not only stimulates UV protective screens but also affects plant defence mechanisms, such as HGL-DTGs accumulation, and modulates ecological interactions of N. attenuata with its herbivores in nature. [ABSTRACT FROM AUTHOR]

The JASMONATE ZIM DOMAIN (JAZ) proteins function as negative regulators of jasmonic acid signaling in plants. We cloned 12 JAZ genes from native tobacco (Nicotiana attenuata), including nine novel JAZs in tobacco, and examined their expression in plants that had leaves elicited by wounding or simulated herbivory. Most JAZ genes showed strong expression in the elicited leaves, but NaJAZg was mainly expressed in roots. Another novel herbivory-elicited gene, NaJAZh, was analyzed in detail. RNA interference suppression of this gene in inverted-repeat (ir)JAZh plants deregulated a specific branch of jasmonic acid-dependent direct and indirect defenses: irJAZh plants showed greater trypsin protease inhibitor activity, 17-hydroxygeranyllinalool diterpene glycosides accumulation, and emission of volatile organic compounds from leaves. Silencing of NaJAZh also revealed a novel cross talk in JAZ-regulated secondary metabolism, as irJAZh plants had significantly reduced nicotine levels. In addition, irJAZh spontaneously developed leaf necrosis during the transition to flowering. Because the lesions closely correlated with the elevated expression of programmed cell death genes and the accumulations of salicylic acid and hydrogen peroxide in the leaves, we propose a novel role of the NaJAZh protein as a repressor of necrosis and/or programmed cell death during plant development. [ABSTRACT FROM AUTHOR]

Two models of potato ( Solanum tuberosum L.) tuberization in vitro (intact plants and single nodes) were used to study the role of cytokinins in this process. We applied hormone in two different ways. The exogenous addition of 10 mg · L N -benzyladenine (BA) into the tuberization medium resulted in advanced tuber formation in intact plants, and microtubers appeared 10-20 days earlier than in the experiments in which no cytokinin was supplied. Transformation with the Agrobacterium tumefaciens ipt gene provided potato clones with endogenously elevated cytokinin levels (3-20 times higher zeatin riboside content in different clones). The onset of tuberization in intact ipt-transformed plants with low transgene expression was advanced in comparison with control material, and exogenously applied BA further promoted the tuberization process. On the contrary, tuberization was strongly inhibited in ipt-transformed nodes, and an external increase of the cytokinin level caused complete inhibition of expiant growth. In untransformed (control) nodes cytokinin application resulted in primary and secondary tuber formation, which depended on the BA concentration in cultivation media. [ABSTRACT FROM AUTHOR]

Depending on geographical location, plants are exposed to variable amounts of UVB radiation and herbivore attack. Because the role(s) of UVB in the priming and/or accumulation of plant defence metabolites against herbivores are not well understood, we used field-grown Nicotiana attenuata plants to explore the effects of UVB on herbivore performance. Consistent with previous reports, UVB-exposed plants accumulated higher levels of ultraviolet (UV)-absorbing compounds (rutin, chlorogenic acid, crypto-chlorogenic acid and dicaffeoylspermidine). Furthermore, UVB increased the accumulation of jasmonic acid, jasmonoyl-L-isoleucine and abscisic acid, all phytohormones which regulate plant defence against biotic and abiotic stress. In herbivore bioassays, N. attenuata plants experimentally protected from UVB were more infested by mirids in three consecutive field seasons. Among defence metabolites measured, 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) showed strongly altered accumulation patterns. While constitutive HGL-DTGs levels were higher under UVB, N. attenuata plants exposed to mirid bugs (Tupiocoris notatus) had still more HGL-DTGs under UVB, and mirids preferred to feed on HGL-DTGs-silenced plants when other UVB protecting factors were eliminated by UVB filters. We conclude that UVB exposure not only stimulates UV protective screens but also affects plant defence mechanisms, such as HGL-DTGs accumulation, and modulates ecological interactions of N. attenuata with its herbivores in nature., (© 2012 Blackwell Publishing Ltd.)

Tobacco BY-2 class IV chitinases (TBC-1, TBC-3) were rapidly and transiently induced by the beta-1,3-, 1,6-glucan elicitor from Alternaria alternata 102 (AaGlucan). The full-length cDNA and 5'-flanking region of a gene encoding class IV chitinases were isolated on the basis of the amino acid sequence of TBC-1. Sequence analysis indicated that NtChitIV encoded TBC-1, TBC-3, or both. Since purified TBC-1 and TBC-3 from BY-2 cells lack a chitin binding domain in the N-terminal region, these enzymes suggested to be derived from NtChitIV by post-translational proteolytic processing. The transcripts of NtChitIV accumulated rapidly within 1h after treatment with AaGlucan. Accumulation was maximal 3h after treatment. Reporter gene assays were used to analyze the promoter regions involved in the transcriptional control of NtChitIV, and these assays revealed that the 1.89-kb NtChitIV promoter was activated by AaGlucan but not by salicylic acid (SA) or methyl jasmonate (MeJA). The AaGlucan-induced transcriptional activation via 1.89-kb NtChitIV promoter was attenuated by pretreatment with SA or MeJA. These results suggest that NtChitIV expression is particularly induced by AaGlucan and that the AaGlucan-dependent signaling pathway is different from the SA- and MeJA-dependent signaling pathways.