Abstract
The objective of this study was to determine the effect of short‐term (4 days) and long‐term (8 days) heat stress (35°C) on sink activity of maize ( Zea mays L.) kernels. Beginning at 3 days after pollination (DAP) kernels were grown in vitro at 25°C and 24 h later were transferred to 35°C for either 4 or 8 days. Each treatment had a control that was maintained continously at 25°C. Two experiments were designed to examine the uptake and distribution of 14 C among hexoses, sucrose and starch in the pedicel placento‐chalazal (pedicel/p‐c). endosperm, and pericarp tissues of kernels exposed to heat stress for 4 or 8 days. Kernels cultured in vitro were placed in 14 C‐sucrose medium either during the period of heat stress (experiment 1; 5 to 13 DAP) or immediately following heat‐stress treatments (experiment 2; 10 to 22 DAP). In both experiments no significant effect of heat stress was observed on the total radioactivity accumulated in the kernels until about 17 DAP, after which heat‐stressed kernels accumulated less 14 C than the control. During the linear fill period, the endosperm of kernels exposed to heat stress accumulated more radioactivity associated with hexoses and sucrose and less radioactivity incorporated into starch, as compared to the control. Kernels heat stressed for 4 days showed a partial recovery in starch synthesis by 21 DAP, but to levels of only 65% of that of the control. Kernels heat stressed for 8 days did not recover. When 14 C‐sucrose was supplied during the heat stress period (5–13 DAP). kernels from all treatments accumulated more hexoses that sucrose in the pedicel/p‐c. However, during the period following heat stress (10–22 DAP), pedicel/p‐c accumulated sucrose, but only in kernels exposed to long‐term heat stress. Soluble invertase activity was inhibited by both short‐term and long‐term heat stress, whereas the activity of insoluble invertase was affected only by long‐term heat stress. These results support the hypothesis that the disruption of kernel growth and more particularly endosperm starch biosynthesis, in response to heat stress, is mainly associated with changes in carbon utilization and partitioning between the different nonstructural carbohydrates within the endosperm rather than with a limitation in carbon supply to the kernel. Therefore, the effect on sink activity does not seem to be attributable to a thermal disruption of kernel uptake of sugars, but rather it is a consequence of heat perturbation of other physiological processes such as endosperm sugar metabolism and starch biosynthesis.
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Claims 11
Claim · model-written summary
Heat did not significantly change total kernel radioactivity until about 17 DAP.
- Treatment
- heat stresse0
- Outcome
- total radioactivity accumulated in the kernelse0
- Qualifier
- until about 17 DAPe0
Zea maysNot reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“no significant effect of heat stress was observed on the total radioactivity accumulated in the kernels until about 17 DAP”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
After 17 DAP heat-stressed kernels accumulated less 14 C than controls.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“after which heat‐stressed kernels accumulated less 14 C than the control”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Heat raised endosperm radioactivity associated with hexoses and sucrose.
- Treatment
- heat stresse0
- Outcome
- radioactivity associated with hexoses and sucrosee0
- Direction
- moree0
- Comparator
- the controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“endosperm of kernels exposed to heat stress accumulated more radioactivity associated with hexoses and sucrose and less radioactivity incorporated into starch, as compared to the control”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Heat reduced endosperm radioactivity incorporated into starch.
- Treatment
- heat stresse0
- Outcome
- radioactivity incorporated into starche0
- Direction
- lesse0
- Comparator
- the controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“endosperm of kernels exposed to heat stress accumulated more radioactivity associated with hexoses and sucrose and less radioactivity incorporated into starch, as compared to the control”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Four-day heat allowed partial starch synthesis recovery to 65% of control by 21 DAP.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Kernels heat stressed for 4 days showed a partial recovery in starch synthesis by 21 DAP, but to levels of only 65% of that of the control”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Eight-day heat did not permit starch synthesis recovery.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Kernels heat stressed for 8 days did not recover”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
During heat, all pedicel treatments accumulated more hexoses than sucrose.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“kernels from all treatments accumulated more hexoses that sucrose in the pedicel/p‐c”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Following heat, pedicel sucrose accumulated only after long-term heat.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“pedicel/p‐c accumulated sucrose, but only in kernels exposed to long‐term heat stress”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Both heat durations inhibited soluble invertase.
- Treatment
- short‐term and long‐term heat stresse0
- Gene
- Soluble invertasee0
- Outcome
- Soluble invertase activitye0
- Direction
- inhibitede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soluble invertase activity was inhibited by both short‐term and long‐term heat stress”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Only long-term heat affected insoluble invertase activity.
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the activity of insoluble invertase was affected only by long‐term heat stress”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
Claim · model-written summary
Authors attribute heat-disrupted starch synthesis mainly to altered endosperm carbon partitioning.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“disruption of kernel growth and more particularly endosperm starch biosynthesis, in response to heat stress, is mainly associated with changes in carbon utilization and partitioning between the different nonstructural carbohydrates within the endosperm”
t0“Heat stress effects on sink activity of developing maize kernels grown in vitro”
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