Abstract
The first topic area of this thesis involved studies on the accumulation and translocation of glucosinolates (GSs), bioactive secondary plant compounds, in broccoli plants. Changes in GS accumulation and gene expression levels in response to exogeneous methyl jasmonate (MeJA) treatment were analyzed in different tissue types at different developmental stages of broccoli. Greater accumulation of GSs with MeJA treatment was observed in apical leaves of broccoli seedlings and florets of plants at harvest maturity. Increases in indolyl GS in apical leaves of seedlings and florets were coupled with the up-regulation of indolyl GS biosynthesis genes. The accumulation of indolyl GSs appears to be modulated by MeJA treatment in an organ-specific manner for optimal distribution of defense substances in the plant. Metabolic profiling of hydrophilic metabolites using GC-MS demonstrated increased accumulation of various phenolics, ascorbates and amino acids in broccoli tissues after MeJA treatment. Distinct changes in carbohydrate levels observed between different tissues (vegetative leaves and floret tissues) of broccoli plants after treatment suggest that carbon metabolism is differentially modulated by MeJA treatment in different tissue types depending on sink-source relationships. Reduced levels of hexose sugars and tricarboxylic acid intermediates after MeJA treatment may reflect the increased requirement for carbon and energy needed to drive secondary product biosynthesis to accumulate metabolites for defense against insects and other herbivores. Substantial increases of indolyl and aromatic GSs after exogenous treatment with MeJA in stem and petioles of seedlings and the existence of intact indolyl-GS forms in phloem exudates suggest enhanced de novo synthesis in combination with active transport. Indoly GSs share structural similarities with the auxin, IAA, and may interact with components of the auxin transport system for intra- and extra-cellular transport or translocation. Application of the auxin efflux inhibitor, 1-naphthylphthalamic acid (NPA) reduced MeJA-mediated accumulation of indolyl GSs in broccoli florets and seedling tissues. NPA did not inhibit expression of indolyl GS biosynthesis genes shown to be upregulated by MeJA treatment or the accumulation of tryptophan, the amino acid precursor of indolyl GSs. Exogenous application of benzyl GS to Arabidopsis roots induced ectopic expression of the PIN1 protein associated with the auxin transport system similar to treatment with NPA, again suggesting GS interaction with the auxin efflux carrier system. The inhibitory effect of NPA on MeJA-mediated accumulation of GS may be due to competitive binding of NPA to auxin efflux carrier components and that GS transport is mediated by the auxin transport system. The inhibitory effect of NPA on indolyl and aromatic GS accumulation and the bioactivity of exogenous treatment of these GS compounds in PIN1 localization, Arabidopsis root growth, and gravitrophic response suggest that indolyl and aromatic GSs may be antagonistic to IAA transport and biosynthesis. Indolyl and aromatic GSs can also be potentially converted into IAA by hydrolysis. This intrinsic feature of GSs may be the part of a sophisticated regulatory process where the metabolic pathways in the plant shift from active growth to a reversible defense posture in response to biotic or abiotic stress. It seems likely that indolyl and aromatic GSs are important compounds that provide connections between jasmonate and auxin signaling. Further studies are required to reveal the regulatory mechanism for crosstalk between the two hormones. The third part of this research was to investigate effect of selenium fertilization and MeJA treatment on accumulation of GSs in broccoli florets. Increasing dietary intake of the element selenium (Se) has been shown to reduce the risk of cancer. Simultaneous enhancement of both Se and GS concentrations in broccoli floret tissue were conducted through the combined treatment of MeJA with Se fertilization. A low level of Se fertilization (concentration) with MeJA treatment displayed no significant changes in total aliphatic GS concentrations with 90% and 50% increases in indolyl and total GSs concentrations, respectively. This result suggests that Se- and GS-enriched broccoli with improved health-promoting properties can be generated by this combined treatment. The second topic of this thesis was conducted to provide basic information required to improve biomass quality and productivity and develop tools for gene transformation in Miscanthus x giganteus. The perennial rhizomatous grass, Miscanthus x giganteus is an ideal biomass crop due to its rapid vegetative growth and high biomass yield potential. As a naturally occurring sterile hybrid, M. x giganteus must be propagated vegetatively by mechanicalling divided rhizomes or from micropropagated plantlets. The effect of callus type, age and culture methods on regeneration competence was studied to improve regeneration efficiency and shorten the period of tissue culture in M. x giganteus propagation. Seven lignin biosynthesis genes and one putative flowering gene were isolated from M. x giganteus by PCR reactions using maize othologous sequences. Southern hybridization and nuclear DNA content analysis indicated that the genes isolated from M. x giganteus exist in the genome of other Miscanthus species as multiple copies. Analysis of lignin content and histological staining of lignin deposition indicated that higher lignin content is found in mature stem node tissues compared to young leaves and apical stem nodal tissues. Cell wall lignification is associated with increasing tissue maturity in Miscanthus species. RNAi and antisense constructs harboring sequences of these genes were developed to generate Miscanthus transgenic plants with suppressed of lignin biosynthesis and delayed flowering.
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Claims 12
Claim · model-written summary
MeJA treatment increased glucosinolate accumulation in apical leaves of broccoli seedlings.
- Taxon
- broccoli
Brassica oleracea var. italicae0 - Organ / stage
- apical leavese0
- Treatment
- MeJA treatmente0
- Outcome
- accumulation of GSse0
- Direction
- Greatere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Greater accumulation of GSs with MeJA treatment was observed in apical leaves of broccoli seedlings and florets of plants at harvest maturity”
Claim · model-written summary
Indolyl glucosinolate increases in broccoli apical leaves and florets are associated with up-regulation of indolyl GS biosynthesis genes.
- Taxon
- broccoliBrassica oleracea var. italicae1
- Gene
- indolyl GS biosynthesis genese0
- Outcome
- indolyl GSe0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Increases in indolyl GS in apical leaves of seedlings and florets were coupled with the up-regulation of indolyl GS biosynthesis genes”
e1“Changes in GS accumulation and gene expression levels in response to exogeneous methyl jasmonate (MeJA) treatment were analyzed in different tissue types at different developmental stages of broccoli”
Claim · model-written summary
MeJA treatment increased phenolics, ascorbates and amino acids in broccoli tissues.
- Taxon
- broccoliBrassica oleracea var. italicae0
- Treatment
- MeJA treatmente0
- Outcome
- phenolics, ascorbates and amino acidse0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Metabolic profiling of hydrophilic metabolites using GC-MS demonstrated increased accumulation of various phenolics, ascorbates and amino acids in broccoli tissues after MeJA treatment”
Claim · model-written summary
MeJA treatment reduced hexose sugars and tricarboxylic acid intermediates in broccoli.
- Taxon
- broccoliBrassica oleracea var. italicae1
- Treatment
- MeJA treatmente0
- Outcome
- hexose sugars and tricarboxylic acid intermediatese0
- Direction
- Reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Reduced levels of hexose sugars and tricarboxylic acid intermediates after MeJA treatment”
e1“Changes in GS accumulation and gene expression levels in response to exogeneous methyl jasmonate (MeJA) treatment were analyzed in different tissue types at different developmental stages of broccoli”
Claim · model-written summary
The auxin efflux inhibitor NPA reduced MeJA-mediated accumulation of indolyl GSs in broccoli florets and seedling tissues.
- Taxon
- broccoliBrassica oleracea var. italicae0
- Treatment
- 1-naphthylphthalamic acid (NPA)e0
- Outcome
- accumulation of indolyl GSse0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Application of the auxin efflux inhibitor, 1-naphthylphthalamic acid (NPA) reduced MeJA-mediated accumulation of indolyl GSs in broccoli florets and seedling tissues”
Claim · model-written summary
Seven lignin biosynthesis genes and one putative flowering gene were isolated from Miscanthus x giganteus.
- Taxon
- Miscanthus x giganteus
Miscanthus ×giganteust0 - Gene
- lignin biosynthesis genese0
- Outcome
- isolatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“lignin biosynthesis genes and putative flowering gene in Miscanthus x giganteus”
e0“Seven lignin biosynthesis genes and one putative flowering gene were isolated from M. x giganteus by PCR reactions”
Claim · model-written summary
Lignin content is higher in mature stem node tissues than in young leaves of Miscanthus x giganteus.
- Taxon
- Miscanthus x giganteusMiscanthus ×giganteust0
- Organ / stage
- mature stem node tissuese0
- Outcome
- lignin contente0
- Direction
- highere0
- Comparator
- young leavese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“lignin biosynthesis genes and putative flowering gene in Miscanthus x giganteus”
e0“higher lignin content is found in mature stem node tissues compared to young leaves and apical stem nodal tissues”
Claim · model-written summary
Low-level selenium fertilization with MeJA caused no significant change in total aliphatic glucosinolate concentrations in broccoli.
- Taxon
- broccoliBrassica oleracea var. italicae1
- Treatment
- low level of Se fertilization (concentration) with MeJA treatmente0
- Outcome
- total aliphatic GS concentrationse0
- Direction
- no significant changese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A low level of Se fertilization (concentration) with MeJA treatment displayed no significant changes in total aliphatic GS concentrations with 90% and 50% increases in indolyl and total GSs concentrations, respectively”
e1“Simultaneous enhancement of both Se and GS concentrations in broccoli floret tissue were conducted through the combined treatment of MeJA with Se fertilization”
Claim · model-written summary
Low-level selenium fertilization with MeJA increased indolyl glucosinolate concentration by 90% in broccoli.
- Taxon
- broccoliBrassica oleracea var. italicae1
- Treatment
- low level of Se fertilization (concentration) with MeJA treatmente0
- Outcome
- indolyl and total GSs concentrationse0
- Direction
- increasese0
- Value
- 90%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A low level of Se fertilization (concentration) with MeJA treatment displayed no significant changes in total aliphatic GS concentrations with 90% and 50% increases in indolyl and total GSs concentrations, respectively”
e1“Simultaneous enhancement of both Se and GS concentrations in broccoli floret tissue were conducted through the combined treatment of MeJA with Se fertilization”
Claim · model-written summary
Low-level selenium fertilization with MeJA increased total glucosinolate concentration by 50% in broccoli.
- Taxon
- broccoliBrassica oleracea var. italicae1
- Treatment
- low level of Se fertilization (concentration) with MeJA treatmente0
- Outcome
- total GSs concentrationse0
- Direction
- increasese0
- Value
- 50%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A low level of Se fertilization (concentration) with MeJA treatment displayed no significant changes in total aliphatic GS concentrations with 90% and 50% increases in indolyl and total GSs concentrations, respectively”
e1“Simultaneous enhancement of both Se and GS concentrations in broccoli floret tissue were conducted through the combined treatment of MeJA with Se fertilization”
Claim · model-written summary
The combined selenium and MeJA treatment can generate Se- and GS-enriched broccoli with improved health-promoting properties.
- Taxon
- broccoliBrassica oleracea var. italicae0
- Treatment
- combined treatmente0
- Outcome
- Se- and GS-enriched broccolie0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This result suggests that Se- and GS-enriched broccoli with improved health-promoting properties can be generated by this combined treatment”
Claim · model-written summary
Exogenous benzyl GS induced ectopic expression of the PIN1 protein in Arabidopsis roots, similar to NPA treatment.
- Taxon
- Arabidopsis
Arabidopsise0 - Treatment
- benzyl GSe0
- Outcome
- expression of the PIN1 proteine0
- Direction
- inducede0
- Comparator
- treatment with NPAe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Exogenous application of benzyl GS to Arabidopsis roots induced ectopic expression of the PIN1 protein associated with the auxin transport system similar to treatment with NPA”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.