Abstract
Abstract Background The kernel number of maize ( Zea mays L.) at maturity is mainly determined at the time around pollination. Kernel abortion frequently occurs during this period, leading to grain yield depressions. Plasma membrane (PM) H + ‐ATPase was identified as a key enzyme responsible for supply of assimilates to the developing maize kernels shortly after pollination. Aims This study aimed at stimulating PM H + ‐ATPase activity in the kernels by in vivo application of the auxin indole‐3‐acetic acid (IAA) to maize plants at flowering, leading to an improved hexose uptake and finally to a better kernel set. Methods Maize plants were cultivated under well‐watered conditions using the container technique. IAA was applied to unstressed maize plants twice, 2 days before controlled pollination and at pollination (application rate per plant: 1.9 mL of 1.5 mM IAA). The developing kernels were harvested 2 days after pollination, and PM vesicles were isolated and purified using two‐phase partitioning. Results The in vitro hydrolytic activity of the PM H + ‐ATPase was significantly stimulated by 22% due to in vivo IAA application (control: 0.99 ± 0.05, IAA treatment: 1.21 ± 0.03* μmol inorganic phosphate mg –1 protein min –1 ). V max was significantly increased by IAA treatment, whereas K m was reduced. The maximal pH gradient (Δ A 492 ) at the PM was increased by 10% (control: 0.071 ± 0.002, IAA treatment: 0.078 ± 0.002*). IAA caused a significant increase of PM H + ‐ATPase abundance in the vesicles. Concentrations of sucrose and hexoses as well as acid invertase activity in the kernels were unaffected by IAA treatment. However, at maturity kernel numbers per cob were significantly decreased causing grain yield reductions of 19%. Conclusions Increased PM H + ‐ATPase activity could not be translated into grain yield improvements. Probably the auxin application occurred too early during kernel development. As cytokinins play a key role during pollination, auxin application at this stage may have disturbed the phytohormone balance, causing disruption of cell division and a rather early onset of cell extension due to increased IAA concentrations. In further studies, it should be tested if applications of cytokinin at flowering or of IAA at a later growth stage have positive impacts on kernel set.
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Claims 8
Claim · model-written summary
In vivo IAA application stimulated the in vitro hydrolytic activity of PM H+-ATPase in maize kernels by 22%.
- Treatment
- in vivo IAA applicatione0
- Gene
- PM H + ‐ATPasee0
- Outcome
- in vitro hydrolytic activitye0
- Direction
- stimulatede0
- Value
- 22%e0
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e0“The in vitro hydrolytic activity of the PM H + ‐ATPase was significantly stimulated by 22% due to in vivo IAA application”
Claim · model-written summary
IAA treatment significantly increased Vmax of the plasma membrane H+-ATPase in maize.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e1“V max was significantly increased by IAA treatment, whereas K m was reduced”
Claim · model-written summary
IAA treatment reduced Km of the plasma membrane H+-ATPase in maize.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e1“V max was significantly increased by IAA treatment, whereas K m was reduced”
Claim · model-written summary
IAA application increased the maximal pH gradient at the plasma membrane by 10%.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e0“The in vitro hydrolytic activity of the PM H + ‐ATPase was significantly stimulated by 22% due to in vivo IAA application”
e2“The maximal pH gradient (Δ A 492 ) at the PM was increased by 10%”
Claim · model-written summary
IAA caused a significant increase in PM H+-ATPase abundance in the vesicles of maize.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e3“IAA caused a significant increase of PM H + ‐ATPase abundance in the vesicles”
Claim · model-written summary
IAA treatment left sucrose and hexose concentrations and acid invertase activity in kernels unaffected.
- Organ / stage
- kernelse4
- Treatment
- IAA treatmente4
- Outcome
- Concentrations of sucrose and hexoses as well as acid invertase activitye4
- Direction
- unaffectede4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e4“Concentrations of sucrose and hexoses as well as acid invertase activity in the kernels were unaffected by IAA treatment”
Claim · model-written summary
Kernel numbers per cob were significantly decreased at maturity after in vivo IAA application.
- Organ / stage
- cobe5
- Treatment
- in vivo IAA applicatione0
- Outcome
- kernel numbers per cobe5
- Direction
- decreasede5
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e0“The in vitro hydrolytic activity of the PM H + ‐ATPase was significantly stimulated by 22% due to in vivo IAA application”
e5“However, at maturity kernel numbers per cob were significantly decreased causing grain yield reductions of 19%”
Claim · model-written summary
IAA application caused grain yield reductions of 19% in maize.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize plants”
e0“The in vitro hydrolytic activity of the PM H + ‐ATPase was significantly stimulated by 22% due to in vivo IAA application”
e5“However, at maturity kernel numbers per cob were significantly decreased causing grain yield reductions of 19%”
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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.