Root cooling strongly affects diel leaf growth dynamics, water and carbohydrate relations inRicinus communis

Abstract

In laboratory and greenhouse experiments with potted plants, shoots and roots are exposed to temperature regimes throughout a 24 h (diel) cycle that can differ strongly from the regime under which these plants have evolved. In the field, roots are often exposed to lower temperatures than shoots. When the root-zone temperature in Ricinus communis was decreased below a threshold value, leaf growth occurred preferentially at night and was strongly inhibited during the day. Overall, leaf expansion, shoot biomass growth, root elongation and ramification decreased rapidly, carbon fluxes from shoot to root were diminished and carbohydrate contents of both root and shoot increased. Further, transpiration rate was not affected, yet hydrostatic tensions in shoot xylem increased. When root temperature was increased again, xylem tension reduced, leaf growth recovered rapidly, carbon fluxes from shoot to root increased, and carbohydrate pools were depleted. We hypothesize that the decreased uptake of water in cool roots diminishes the growth potential of the entire plant -especially diurnally, when the growing leaf loses water via transpiration. As a consequence, leaf growth and metabolite concentrations can vary enormously, depending on root-zone temperature and its heterogeneity inside pots.

Control of Leaf Expansion: A Developmental Switch from Metabolics to Hydraulics

“…Water supply to the growing tissues, therefore, appears as a key point to balance the increasing competition for water between growth and transpiration as the leaf expands. The impact on growth of this competition has been well documented in monocots but also in dicots such as sunflower (Boyer, 1968), castor bean (Ricinus communis; Poiré et al, 2010a), and several halophytic species (Rozema et al, 1987). However, to our knowledge, our study is the first one reporting a progressive establishment of hydraulic constraint on leaf growth during its ontogeny.…”

Can we improve heterosis for root growth of maize by selecting parental inbred lines with different temperature behaviour?

“…Under such conditions, temperature variations throughout 24 h can be considerable; especially when plants are grown under relatively high light intensities. Then, topsoil pot temperatures can exceed air temperature by 108C owing to the radiative heat input and the negligible thermal buffering capacity of small pots [11], adding up to the numerous perils of pot experiments [40]. Minuscule root systems of plants such as Arabidopsis thaliana would, under such circumstances, have an enormous advantage if their growth temperature optimum was wider than usual.…”

“…Shoot growth and yield strongly depend on the performance of the root system [7]. In maize, it is well known that root zone temperature strongly affects leaf growth and shoot biomass [8,9], mediated by pronounced alterations in shoot metabolism [10] and shortterm growth dynamics [11]. Low root zone temperatures induce decreased root growth and this in turn hampers shoot development by altered water relations [12,13] and carbohydrate metabolism [11].…”

“…In maize, it is well known that root zone temperature strongly affects leaf growth and shoot biomass [8,9], mediated by pronounced alterations in shoot metabolism [10] and shortterm growth dynamics [11]. Low root zone temperatures induce decreased root growth and this in turn hampers shoot development by altered water relations [12,13] and carbohydrate metabolism [11]. Because root zone temperatures are modulated not only throughout the season, but also throughout day-night cycles in topsoil regions, the question as to how intensely root growth is hampered by sub-or supra-optimal temperatures is highly relevant also in the context of the overall development of the shoot, which is a main trait of plant breeding.…”

Temporal Changes in Allocation and Partitioning of New Carbon as 11C Elicited by Simulated Herbivory Suggest that Roots Shape Aboveground Responses in Arabidopsis

“…To determine whether roots effectively compete with defense-induced primary and secondary metabolites for carbon resources, root chilling treatments were used to disrupt carbon flow between above-and belowground tissues. The inhibition of phloem transport by chilling roots has been particularly well investigated (Geiger, 1969;Minchin et al, , 1994Poiré et al, 2010;Thorpe et al, 2010) and can be accomplished with minor drops in temperature . In our experiments, individual plants were seated inside an epoxy-sealed pot affixed in an ice water bath (0°C; Supplemental Fig.…”