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The effect of source or sink temperature on photosynthesis and 14 C‐partitioning in and export from a source leaf of Alstroemeria
Author(s) -
Leonardos Evangelos D.,
Tsujita M. James,
Grodzinski Bernard
Publication year - 1996
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1996.tb00517.x
Subject(s) - starch , photosynthesis , chemistry , sugar , sucrose , horticulture , botany , food science , biology , biochemistry
The influence of source and sink temperature on leaf net C exchange rate (NCER), export, and partitioning in the C 3 monocotyledon Alstroemeria sp. cv. Jacqueline were examined. Leaf (i.e. source) temperature was varied between 12 and 35°C while source leaves were exposed to photorespiratory and nonphotorespiratory conditions during a 2‐h steady‐state 14 CO 2 labelling period. Between 12 and 20°C, at ambient CO 2 and O 2 , leaf NCER and export were similar with maximum rates of 9.71 ± 0.51 and 3.06 ± 0.36 μmol C m ‐2 s ‐1 , respectively. Both NCER and export decreased above 20°C. At 35°C NCER was 30% of the rate at 20°C, but export was totally inhibited. Between 12 and 35°C, at the end of the 2‐h feeding period, 14 C was partitioned in the leaf as ethanol insolubles (3–10%), H 2 O solubles (88–92%), and chloroform solubles (2–8%). However, above 25°C, less 14 C was recovered in the starch fraction and more in the sugar fractions. At all temperatures, 86 to 94% of the labelled sugars was 14 C‐sucrose. In nonphotorespiratory conditions (i.e. 1 800 μI I ‐1 CO 2 and 2% O 2 ). NCER and export were higher than the rates obtained at ambient CO 2 and O 2 at each temperature. Carbon dioxide enrichment sustained high NCER and export rates even at 35°C, Although CO 2 enrichment increased partitioning of 14 C into starch, starch synthesis at 35°C was markedly reduced. Cooling the root‐zone mass (i.e. a dominant sink) to 10°C, which simulated the commercial practice used to induce flowering, had no significant effect on source leaf NCER and export rates either during a 2‐h steady‐state labelling period or subsequently during a 21‐h light‐dark chase period. Furthermore, partitioning of 14 C among leaf products at the end of the feed‐chase period was not affected. Additional pulse and chase experiments using 11 CO 2 fed to source leaves of control and root‐cooled plants showed that there was no difference in the direction of movement of 11 C‐assimilates towards the flower or the root zone as a consequence of root cooling. Together, the data indicate that changing source strength, by manipulating photosynthesis and photorespiration, by varying the leaf temperature had a more profound effect on leaf export than manipulating sink activity.