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. 2021 Jun;230(5):1911-1924.
doi: 10.1111/nph.17302. Epub 2021 Apr 26.

The mechanism of sugar export from long conifer needles

Johannes Liesche  1   2 , Christopher Vincent  3 , Xiaoyu Han  1 , Maciej Zwieniecki  4 , Alexander Schulz  5 , Chen Gao  5 , Rodrigue Bravard  6 , Sean Marker  6 , Tomas Bohr  6
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Free article

The mechanism of sugar export from long conifer needles

Johannes Liesche et al. New Phytol. 2021 Jun.
Free article

Abstract

The green leaves of plants are optimised for carbon fixation and the production of sugars, which are used as central units of carbon and energy throughout the plant. However, there are physical limits to this optimisation that remain insufficiently understood. Here, quantitative anatomical analysis combined with mathematical modelling and sugar transport rate measurements were used to determine how effectively sugars are exported from the needle-shaped leaves of conifers in relation to leaf length. Mathematical modelling indicated that phloem anatomy constrains sugar export in long needles. However, we identified two mechanisms by which this constraint is overcome, even in needles longer than 20 cm: (1) the grouping of transport conduits, and (2) a shift in the diurnal rhythm of sugar metabolism and export in needle tips. The efficiency of sugar transport in the phloem can have a significant influence on leaf function. The constraints on sugar export described here for conifer needles are likely to also be relevant in other groups of plants, such as grasses and angiosperm trees.

Keywords: carbohydrate allocation; conifers; gymnosperms; leaf anatomy; phloem loading; sugar transport.

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