Changes in water content and distribution in Quercus ilex leaves during progressive drought assessed by in vivo 1H magnetic resonance imaging.

Abstract

BackgroundDrought is a common stressor in many regions of the world and current climatic global circulation models predict further increases in warming and drought in the coming decades in several of these regions, such as the Mediterranean basin. The changes in leaf water content, distribution and dynamics in plant tissues under different soil water availabilities are not well known. In order to fill this gap, in the present report we describe our study withholding the irrigation of the seedlings of Quercus ilex, the dominant tree species in the evergreen forests of many areas of the Mediterranean Basin. We have monitored the gradual changes in water content in the different leaf areas, in vivo and non-invasively, by 1H magnetic resonance imaging (MRI) using proton density weighted (ρw) images and spin-spin relaxation time (T2) maps.Resultsρw images showed that the distal leaf area lost water faster than the basal area and that after four weeks of similar losses, the water reduction was greater in leaf veins than in leaf parenchyma areas and also in distal than in basal leaf area. There was a similar tendency in all different areas and tissues, of increasing T2 values during the drought period. This indicates an increase in the dynamics of free water, suggesting a decrease of cell membranes permeability.ConclusionsThe results indicate a non homogeneous leaf response to stress with a differentiated capacity to mobilize water between its different parts and tissues. This study shows that the MRI technique can be a useful tool to follow non-intrusively the in vivo water content changes in the different parts of the leaves during drought stress. It opens up new possibilities to better characterize the associated physiological changes and provides important information about the different responses of the different leaf areas what should be taken into account when conducting physiological and metabolic drought stress studies in different parts of the leaves during drought stress.

Evidence of current impact of climate change on life: a walk from genes to the biosphere

“…As reported in the previous section, a shift of protein content occurs under drought from proteins related to photosynthesis and carboxylation to proteins linked to antistress systems (Table ). Fine‐scale studies using 1 H nuclear magnetic resonance (NMR) imaging have observed that leaves of the Mediterranean tree Quercus ilex under prolonged drought are able to maintain water in parenchymal tissues for a longer time than in vascular tissues, which allows the most active parts of the leaves to be more hydrated for a longer time (Sardans et al ., ). These conservative mechanisms are frequently able to minimize the negative effects of drought on plant growth (Molina‐Montenegro et al ., ; Peñuelas et al ., ,b).…”

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“…Whereas many alternatives exist to quantify water flow in vivo, ranging from the use of heat as a tracer [31] to magnetic resonance imaging [32][33][34] and neutron imaging [35], the options are much more limited for in vivo, non-invasive carbon quantification. This is where the isotope 11 C Glossary Apoplast: continuum of extracellular spaces and cell walls.…”

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“…, 2011). Quercus ilex leaves have been used to monitor what changes occur in vivo over the course of progressive drought (Sardans et al. , 2010).…”