Abstract
Poor filling of grains in the basal spikelets of large size panicles bearing numerous spikelets has been a major limitation in attempts to increase the rice production to feed the world’s increasing population. Considering that biotechnological intervention could play important role in overcoming this limitation, the role of cytokinin in grain filling was investigated based on the information on cell proliferating potential of the hormone and reports of its high accumulation in immature seeds. A comparative study considering two rice varieties differing in panicle compactness, lax-panicle Upahar and compact-panicle OR-1918, revealed significant difference in grain filling, cytokinin oxidase (CKX) activity and expression, and expression of cell cycle regulators and cytokinin signaling components between the basal and apical spikelets of OR-1918, but not of Upahar. Exogenous application of cytokinin (6-Benzylaminopurine, BAP) to OR-1918 improved grain filling significantly, and this was accompanied by a significant decrease in expression and activity of CKX , particularly in the basal spikelets where the activity of CKX was significantly higher than that in the apical spikelets. Cytokinin application also resulted in significant increase in expression of cell cycle regulators like cyclin dependent kinases and cyclins in the basal spikelets that might be facilitating cell division in the endosperm cells by promoting G1/S phase and G2/M phase transition leading to improvement in grain filling. Expression studies of type-A response regulator ( RR ) component of cytokinin signaling indicated possible role of OsRR3 , OsRR4 and OsRR6 as repressors of CKX expression, much needed for an increased accumulation of CK in cells. Furthermore, the observed effect of BAP might not be solely because of it, but also because of induced synthesis of trans-zeatin (tZ) and N 6 -(Δ 2 -isopentenyl)adenine (iP), as reflected from accumulation of tZR (tZ riboside) and iPR (iP riboside), and significantly enhanced expression of an isopentenyl transferase ( IPT ) isoform. The results suggested that seed-specific overexpression of OsRR4 and OsRR6 , and more importantly of IPT9 could be an effective biotechnological intervention towards improving the CK level of the developing caryopses leading to enhanced grain filling in rice cultivars bearing large panicles with numerous spikelets, and thereby increasing their yield potential.
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Claims 10
Claim · model-written summary
Basal and apical spikelets of OR-1918 differed significantly in grain filling, CKX activity and expression, and cell cycle and cytokinin signaling expression.
- Taxon
- rice
Oryza sativae1 - Material
- OR-1918e0
- Organ / stage
- basal and apical spikeletse0
- Outcome
- grain filling, cytokinin oxidase (CKX) activity and expression, and expression of cell cycle regulators and cytokinin signaling componentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significant difference in grain filling, cytokinin oxidase (CKX) activity and expression, and expression of cell cycle regulators and cytokinin signaling components between the basal and apical spikelets of OR-1918”
e1“two rice varieties differing in panicle compactness, lax-panicle Upahar and compact-panicle OR-1918”
Claim · model-written summary
Upahar showed no corresponding basal versus apical spikelet difference.
- Taxon
- riceOryza sativae1
- Material
- Upahare0
- Organ / stage
- basal and apical spikeletse0
- Outcome
- grain fillinge2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“between the basal and apical spikelets of OR-1918, but not of Upahar”
e1“two rice varieties differing in panicle compactness, lax-panicle Upahar and compact-panicle OR-1918”
e2“significant difference in grain filling, cytokinin oxidase (CKX) activity and expression, and expression of cell cycle regulators and cytokinin signaling components between the basal and apical spikelets of OR-1918”
Claim · model-written summary
BAP significantly improved grain filling in OR-1918.
- Taxon
- riceOryza sativae1
- Material
- OR-1918e0
- Treatment
- Exogenous application of cytokinin (6-Benzylaminopurine, BAP)e0
- Outcome
- grain fillinge0
- Direction
- improvede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Exogenous application of cytokinin (6-Benzylaminopurine, BAP) to OR-1918 improved grain filling significantly”
e1“two rice varieties differing in panicle compactness”
Claim · model-written summary
BAP significantly decreased CKX expression and activity, especially in basal spikelets.
- Taxon
- riceOryza sativae2
- Organ / stage
- basal spikeletse0
- Treatment
- Exogenous application of cytokinin (6-Benzylaminopurine, BAP)e1
- Gene
- CKXe0
- Outcome
- expression and activity of CKXe0
- Direction
- decreasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significant decrease in expression and activity of CKX , particularly in the basal spikelets”
e1“Exogenous application of cytokinin (6-Benzylaminopurine, BAP) to OR-1918”
e2“two rice varieties differing in panicle compactness”
Claim · model-written summary
CKX activity was significantly higher in basal than apical spikelets.
- Taxon
- riceOryza sativae2
- Organ / stage
- basal spikeletse1
- Gene
- CKXe0
- Outcome
- activity of CKXe0
- Direction
- highere0
- Comparator
- apical spikeletse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“activity of CKX was significantly higher than that in the apical spikelets”
e1“particularly in the basal spikelets”
e2“two rice varieties differing in panicle compactness”
Claim · model-written summary
Cytokinin significantly increased expression of cell cycle regulators in basal spikelets.
- Taxon
- riceOryza sativae1
- Organ / stage
- basal spikeletse0
- Treatment
- Cytokinin applicatione0
- Outcome
- expression of cell cycle regulators like cyclin dependent kinases and cyclinse0
- Direction
- increasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Cytokinin application also resulted in significant increase in expression of cell cycle regulators like cyclin dependent kinases and cyclins in the basal spikelets”
e1“two rice varieties differing in panicle compactness”
Claim · model-written summary
OsRR3, OsRR4 and OsRR6 may repress CKX expression.
- Taxon
- riceOryza sativae1
- Gene
- OsRR3 , OsRR4 and OsRR6e0
- Outcome
- CKX expressione0
- Qualifier
- possible rolee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“possible role of OsRR3 , OsRR4 and OsRR6 as repressors of CKX expression”
e1“grain filling in rice cultivars”
Claim · model-written summary
BAP treatment was associated with accumulation of tZR and iPR.
- Taxon
- riceOryza sativae1
- Treatment
- BAPe0
- Outcome
- accumulation of tZR (tZ riboside) and iPR (iP riboside)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“observed effect of BAP might not be solely because of it, but also because of induced synthesis of trans-zeatin (tZ) and N 6 -(Δ 2 -isopentenyl)adenine (iP), as reflected from accumulation of tZR (tZ riboside) and iPR (iP riboside)”
e1“grain filling in rice cultivars”
Claim · model-written summary
BAP treatment significantly enhanced expression of an IPT isoform.
- Taxon
- riceOryza sativae2
- Treatment
- BAPe1
- Gene
- isopentenyl transferase ( IPT )e0
- Outcome
- expression of an isopentenyl transferase ( IPT ) isoforme0
- Direction
- enhancede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significantly enhanced expression of an isopentenyl transferase ( IPT ) isoform”
e1“observed effect of BAP”
e2“grain filling in rice cultivars”
Claim · model-written summary
The authors suggest seed-specific overexpression of OsRR4, OsRR6 and especially IPT9 to improve grain filling and yield potential.
- Taxon
- riceOryza sativae0
- Gene
- OsRR4 and OsRR6e0
- Outcome
- enhanced grain fillinge0
- Qualifier
- rice cultivars bearing large panicles with numerous spikeletse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“seed-specific overexpression of OsRR4 and OsRR6 , and more importantly of IPT9 could be an effective biotechnological intervention towards improving the CK level of the developing caryopses leading to enhanced grain filling in rice cultivars bearing large panicles with numerous spikelets, and thereby increasing their yield potential”
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