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Plants’ internal clocks remember water stress!

Plants optimize their growth by “remembering” water stress and adjusting root water uptake accordingly. These are the groundbreaking findings of researchers at INRA and the Catholic University of Louvain, thanks to a system of precise measurements of growth in a large number of plants in natural conditions. Published in the November 5, 2014 issue of Nature Communications, their research is the first physiological explanation of a mechanism linked to circadian rhythms that contributes to a plant’s evolutionary advantage.

Updated on 07/04/2017
Published on 11/05/2014
Keywords:

Plants respond to natural climatic fluctuations. Their water status ranges from favorable at night to unfavorable in the afternoon, and the drier the ground and air, the more this is the case. That is why plants seem to do well in the morning, tend to wilt in the afternoon, and perk up at night, even when the ground is only partially dry. Organ growth follows the same rhythm: maximum growth occurs at night, minimal growth during the day. Moreover, when plants are observed under continuous light, scientists have noticed that almost all their physiological functions are governed by circadian rhythms, much like in animals (in 24-hour periods). The opening of molecular switches, or aquaporins - and in turn the permeability of roots - reaches a maximum at dawn and a minimum at sunset. These aquaporins therefore foster water transport in the plant in the morning hours when its water needs are at a peak. This provokes daily oscillations in leaf growth under continuous light.

Research carried out at INRA and the Catholic University of Louvain has revealed a new phenomenon: the full range of daily oscillations of leaf growth depends on the water stress the plant experienced in the past. This finding was made possible by a system of precise measurements of the rate of leaf expansion in a large number of plants at three-minute intervals in natural conditions.

The phenomenon may be explained as follows: if plants are exposed to water stress (eg sunny days and dry soil), the gene expression of aquaporins will vary wildly over the course of the day, but only slightly after cloudy days in moist soil. Water movement and leaf growth follow these same oscillations, which depend on the recent history of the plant. Thanks to the mathematical modeling of water transfer from ground to leaf via plant roots, scientists have demonstrated the benefits of such an ability to acclimatize. If plants experience drought, the daily transport of water to the roots is facilitated provided the roots lower their permeability in the afternoon and restore it the following morning via aquaporins. This prevents over-drying of the soil that surrounds the roots, which can become practically impenetrable when it dries out. Conversely, in favorable climatic conditions (moist soil and humid air), strong oscillations in root permeability are detrimental to plant growth. Performance gains or losses mount to 10-15% in either case. By registering water conditions experienced in previous days, plants can anticipate the degree of oscillations that will best foster growth. This study is the first physiological explanation of a mechanism linked to the evolutionary advantage associated with circadian rhythms.

. © INRA
© INRA

By registering water conditions experienced in previous days, plants can anticipate the degree of oscillations that will most effectively promote growth.

On the left side of the chart, plants are exposed to natural light conditions; the grey bars represent night. To the right, plants are exposed to continuous light; the grey bars correspond to “night” in the circadian cycle of plants. The top section records plant growth, while the chart below shows their water status. Red indicates that plants have experienced significant water stress, which leads to unfavorable water status and leaf growth in the afternoon, followed by significant oscillations in continuous light. Green indicates plants that have not experienced water stress and are exposed to favorable conditions, with steady exposure to light.
© INRA, F. Tardieu

Reference:

Caldeira C, Jeanguenin L Chaumont F, Tardieu F. Circadian rhythms of hydraulic conductance and growth are enhanced by drought and improve plant performance. Nature Communications. 5:5365 DOI: 10.1038/ncomms6365 (5 November 2014).

Contact(s)
Scientific contact(s):

  • François Tardieu (+33 (0)4 99 61 26 32) Joint Research Unit for Ecophysiology of Plants under Environmental Stress
Press Relations:
INRA News Office (+33 (0)1 42 75 91 86)
Associated Division(s):
Environment and Agronomy
Associated Centre(s):
Occitanie-Montpellier

François Tardieu, Winner of 2014 INRA Excellence Award

Press kit on François Tardieu

Press release on the 2014 Awards ceremony