The maximal capacity of a leaf to carry out photosynthesis is closely coordinated with the capacity of the foliar vasculature for sugar and water transport, and these features co-vary in response to the growth environment as has been documented in several genotypes of the winter annual Arabidopsis thaliana ( Cohu et al., 2013a, b Adams et al., 2016 Stewart et al., 2016, 2017a, b, 2018). Establishment of the Ei-5 accession, with a low vein density but an apparent overcapacity for water flux through the foliar xylem network, may have been facilitated by a higher level of precipitation in its habitat of origin compared to that of the Col-0 accession. The Ei-5 accession thus further underscores the plasticity of the foliar vasculature by illustrating an example where a higher ratio of tracheary to sieve elements is associated with a lower vein density.
In contrast, previous studies in other systems had reported higher ratios of tracheary to sieve elements and higher transpiration rate to be associated with higher – rather than lower – vein densities. In contrast, the product of vein density × xylem cell number per minor vein was significantly greater in Ei-5 compared to Col-0, and was associated not only with a higher ratio of water-transporting tracheary elements versus sugar-transporting sieve elements but also significantly higher foliar transpiration rates per leaf area in Ei-5. This compensation for low vein density resulted in similar values for the product of vein density × phloem cell number per minor vein in Ei-5 and Col-0, which suggests a similar capacity for foliar sugar export to support similar photosynthetic capacities per unit leaf area. The individual foliar minor veins were larger in Ei-5, with a greater number of vascular cells per vein, compared to Col-0. In addition to having to a lower vein density, Ei-5 grew more slowly, with significantly lower rates of rosette expansion, but had similar capacities for photosynthetic oxygen evolution on a leaf area basis compared to Col-0. Department of Ecology and Evolutionary Biology, University of Colorado Boulder, Boulder, CO, United StatesĪn Arabidopsis thaliana accession with naturally low vein density, Eifel-5 (Ei-5), was compared to Columbia-0 (Col-0) with respect to rosette growth, foliar vein architecture, photosynthesis, and transpiration.Polutchko, Barbara Demmig-Adams and William W.
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