Suboptimal temperature favors reserve formation in biennial carrot (Daucus carota) plants

Abstract

In response to suboptimal temperatures, temperate annual plants often increase root:shoot ratios, build-up carbohydrates and display typical morphological and anatomical changes. We know less about the responses of biennials such as carrot. As a model plant, carrot has the additional feature of two functionally and morphologically distinct root parts: the taproot, which stores carbohydrate and other compounds, and the fibrous root system involved in acquisition of water and nutrients. Here, we analyze the effects of temperature (12 vs 25°C) on growth, carbohydrate accumulation and whole-plant morphology in two carrot cultivars. Our working hypothesis is that suboptimal temperature favors active formation of reserve structures, rather than passive accumulation of storage carbohydrates. In comparison with plants grown at 25°C, plants grown at 12°C had: (1) higher fibrous root:shoot ratio (13%) , (2) thicker (10-15%) and smaller (up to two- to three-fold) leaves, (3) lower leaf cuticular permeance (two- to four-fold), (4) higher taproot:shoot ratio (two-fold), (5) higher phloem:xylem ratios in taproot (two- to six-fold), (6) unchanged percentage dry matter content (%DMC) in leaves, petioles or fibrous roots and (7) higher %DMC in taproot (20%). However, %DMC of individual taproot tissues (phloem and xylem) was unaffected by temperatures and was consistently higher in the phloem (up to 30%). Therefore, the higher %DMC of whole taproots at 12°C was attributed solely to the increased development of phloem tissue. Carrot, therefore, shares many of the most conspicuous elements of temperate plant responses to low temperatures. Consistently with our hypothesis, however, carrots grown at suboptimal temperature promoted reserve structures, rather than the increase in carbohydrate concentration typical of most temperate annual species and woody perennials.

Light, temperature and tocopherol status influence foliar vascular anatomy and leaf function in Arabidopsis thaliana

“…Stewart et al (2016) showed that higher photosynthetic capacities in cool-grown vs hot-grown A. thaliana ecotypes from Sweden and Italy were associated with greater numbers of phloem cells in foliar veins, and that the lower transpiration rates in these cool-grown plants were associated with fewer xylem cells in foliar veins when compared with hot-grown plants (see also Adams et al 2016). These observations are consistent with reports of greater phloem-to-xylem ratios in cold-grown leaves of spring and winter wheat (Equiza and Tognetti 2002) and in the vasculature of carrot root (González et al 2009). Another previous study ) characterized plants grown under a range of conditions, but did not address phloem-to-xylem ratios.…”

“…The comprehensive dataset presented here revealed significant linear positive correlations between all features of xylem anatomy and transpiration rate and between all features of phloem anatomy and photosynthetic capacity across all growth environments despite contrasting acclimation trends to growth light intensity vs growth temperature. Our findings that foliar xylem and phloem features can be adjusted to specific environmental conditions both differentially (increased minor-vein xylem-to-phloem ratio in response to high vs low growth temperature) and in parallel (concomitant increase in minor-vein xylem and phloem in response to high vs low growth light intensity) in a winter annual are consistent with shifts to a greater phloem-to-xylem ratio in response to low growth temperature in spring and winter wheat leaves (Equiza and Tognetti 2002) and in carrot root (González et al 2009) as well as with greater numbers of both phloem and xylem cells in response to high light intensities in kiwifruit (Biasi and Altamura 1996). The absence of correlations between photosynthesis and foliar xylem features in A. thaliana across the entirety of growth conditions used here was driven by the upregulation of photosynthetic capacity in this winter annual under a cool growth regime that did not lead to concomitant increases in xylem features.…”

Sucrose signaling in plants: A world yet to be explored

“…The involvement of Suc in phloem differentiation in in vitro grown plants was showed many decades ago 81 and accordingly, it has been found that conditions that favor Suc accumulation also induce the development of phloem parenchyma (which is the most important sink for assimilates) in carrot roots. 82 In agreement with the role of promoting reserve structures formation, Suc has been found to induce the development of storage organs in different species. The most well-known case is that of potato tuber induction.…”

Ridge‐Furrow Planting System and Wheat Straw Mulching Effects on Dryland Sunflower Yield, Soil Temperature, and Moisture

“…Soil temperature plays a significant role in plant growth and development; nonetheless, the effect of temperature is often implicitly presumed to be correlated with air, but not soil temperature. Recently, it has been reported that soil temperature more closely associates with crop development than air temperature (Sabri et al, 2018; González et al, 2009), so that plant growth is visibly affected by changes in soil temperature (Gan et al, 2013; Pramanik et al, 2015). From the results, we found that the effect of wheat straw mulch on soil temperature was more pronounced during the early stages of growth (V4 and R2 growth stages), because of the sparse crop cover compared to later growth stages (Fig.…”