Abstract
The physiological processes associated with genetic differences in shoot elongation rate (SER) and leaf area expansion rate (LAER) of alfalfa ( Medicago sativa L.) are poorly understood. Our objective was to examine the relationships among SER, LAER, and the concentration and utilization of nonstructural carbohydrates in roots and meristematic shoot tissues of alfalfa. Two genotypes selected for contrasting SER were sampled after 7 d of herbage regrowth in 15‐h photoperiods. Remaining plants were placed in continuous darkness and sampled periodically during the next 144 h (Exp. 1) or 33 h (Exp. 2) of regrowth. In Exp. 1, LAER, concentrations total nonstructural carbohydrate (TNC), and dark respiration rates (R D ) of expanding leaves decreased during the first 48 h of regrowth in continuous darkness. In Exp. 2, LAER declined to 40% of mid‐photoperiod values after 17 h of continuous darkness, while R D of expanding leaves declined to 75% of mid‐photoperiod rates. Concentrations of TNC in expanding leaves declined by Hour 17 of darkness to 19% of mid‐photoperiod concentrations, reflecting trends in R D and especially LAER. In expanding leaves, TNC concentrations greater than 28 g kg −1 dry wt. were necessary for maximum LAER and R D to occur. Averaged over experiments, root TNC concentrations were 185 g kg −1 dry wt. during the initial 17 h of continuous darkness and did not decline significantly. Although roots contained high concentrations of TNC, LAER decreased rapidly within 17 h of continuous darkness. This indicates that expanding leaves may rely upon sources of carbohydrate other than that in roots for growth under C‐limited conditions.
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Claims 8
Claim · model-written summary
In alfalfa expanding leaves, leaf area expansion rate, TNC concentration and dark respiration decreased in continuous darkness during the first 48 h of regrowth.
- Taxon
- alfalfa
Medicago sativae1 - Organ / stage
- expanding leavese2
- Treatment
- continuous darknesse2
- Outcome
- LAER, concentrations total nonstructural carbohydrate (TNC), and dark respiration ratese2
- Direction
- decreasede2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e2“In Exp. 1, LAER, concentrations total nonstructural carbohydrate (TNC), and dark respiration rates (R D ) of expanding leaves decreased during the first 48 h of regrowth in continuous darkness”
Claim · model-written summary
Leaf area expansion rate of alfalfa fell to 40% of mid-photoperiod values after 17 h of continuous darkness.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- continuous darknesse3
- Outcome
- LAERe3
- Direction
- declinede3
- Value
- 40%e3
- Qualifier
- after 17 he3
- Comparator
- mid‑photoperiod valuese3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e3“In Exp. 2, LAER declined to 40% of mid‑photoperiod values after 17 h of continuous darkness”
Claim · model-written summary
Dark respiration of alfalfa expanding leaves fell to 75% of mid-photoperiod rates in continuous darkness.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- expanding leavese4
- Treatment
- continuous darknesse2
- Outcome
- R D of expanding leavese4
- Direction
- declinede4
- Value
- 75%e4
- Comparator
- mid‑photoperiod ratese4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e2“In Exp. 1, LAER, concentrations total nonstructural carbohydrate (TNC), and dark respiration rates (R D ) of expanding leaves decreased during the first 48 h of regrowth in continuous darkness”
e4“while R D of expanding leaves declined to 75% of mid‑photoperiod rates”
Claim · model-written summary
TNC concentration in alfalfa expanding leaves fell to 19% of mid-photoperiod concentrations by hour 17 of darkness.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- expanding leavese5
- Treatment
- darknesse5
- Outcome
- Concentrations of TNC in expanding leavese5
- Direction
- declinede5
- Value
- 19%e5
- Comparator
- mid‑photoperiod concentrationse5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e5“Concentrations of TNC in expanding leaves declined by Hour 17 of darkness to 19% of mid‑photoperiod concentrations”
Claim · model-written summary
TNC concentrations above 28 g kg-1 dry weight were necessary for maximum LAER and dark respiration in alfalfa expanding leaves.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- expanding leavese6
- Compound
- TNCe6
- Outcome
- maximum LAER and R De6
- Value
- 28 g kg −1 dry wt.e6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e6“In expanding leaves, TNC concentrations greater than 28 g kg −1 dry wt. were necessary for maximum LAER and R D to occur”
Claim · model-written summary
Root TNC concentration of alfalfa averaged 185 g kg-1 dry weight during the initial 17 h of continuous darkness.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- roote7
- Treatment
- continuous darknesse7
- Outcome
- root TNC concentrationse7
- Value
- 185 g kg −1 dry wt.e7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e7“Averaged over experiments, root TNC concentrations were 185 g kg −1 dry wt. during the initial 17 h of continuous darkness”
Claim · model-written summary
Root TNC concentration of alfalfa did not decline significantly during continuous darkness.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- continuous darknesse7
- Outcome
- root TNC concentrationse7
- Direction
- did not declinee3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e7“Averaged over experiments, root TNC concentrations were 185 g kg −1 dry wt. during the initial 17 h of continuous darkness”
e3“and did not decline significantly”
Claim · model-written summary
Expanding alfalfa leaves may rely on carbohydrate sources other than root reserves for growth under carbon-limited conditions.
- Taxon
- alfalfaMedicago sativae1
- Outcome
- growthe2
- Qualifier
- sources of carbohydrate other than that in rootse2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“of alfalfa ( Medicago sativa L.)”
e2“expanding leaves may rely upon sources of carbohydrate other than that in roots for growth”
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