The synergy between drought-responsive traits across different organs is crucial in the whole-plant mechanism influencing drought resilience. These organ interactions, however, are poorly... Show moreThe synergy between drought-responsive traits across different organs is crucial in the whole-plant mechanism influencing drought resilience. These organ interactions, however, are poorly understood, limiting our understanding of drought response strategies at the whole-plant level. Therefore, we need more integrative studies, especially on herbaceous species that represent many important food crops but remain underexplored in their drought response. We investigated inflorescence stems and rosette leaves of six Arabidopsis thaliana genotypes with contrasting drought tolerance, and combined anatomical observations with hydraulic measurements and gene expression studies to assess differences in drought response. The soc1ful double mutant was the most drought-tolerant genotype based on its synergistic combination of low stomatal conductance, largest stomatal safety margin, more stable leaf water potential during non-watering, reduced transcript levels of drought stress marker genes, and reduced loss of chlorophyll content in leaves, in combination with stems showing the highest embolism resistance, most pronounced lignification, and thickest intervessel pit membranes. In contrast, the most sensitive Cvi ecotype shows the opposite extreme of the same set of traits. The remaining four genotypes show variations in this drought syndrome. Our results reveal that anatomical, ecophysiological, and molecular adaptations across organs are intertwined, and multiple (differentially combined) strategies can be applied to acquire a certain level of drought tolerance. Show less
The evolution of xylem vessels from tracheids is put forward as a key innovation that boosted hydraulic conductivity and photosynthetic capacities in angiosperms. Yet, the role of xylem anatomy and... Show moreThe evolution of xylem vessels from tracheids is put forward as a key innovation that boosted hydraulic conductivity and photosynthetic capacities in angiosperms. Yet, the role of xylem anatomy and interconduit pits in hydraulic performance across vesselless and vessel-bearing angiosperms is incompletely known, and there is a lack of functional comparisons of ultrastructural pits between species with different conduit types. We assessed xylem hydraulic conductivity and vulnerability to drought-induced embolism in 12 rain forest species from New Caledonia, including five vesselless species, and seven vessel-bearing species with scalariform perforation plates. We measured xylem conduit traits, along with ultrastructural features of the interconduit pits, to assess the relationships between conduit traits and hydraulic efficiency and safety. In spite of major differences in conduit diameter, conduit density, and the presence/absence of perforation plates, the species studied showed similar hydraulic conductivity and vulnerability to drought-induced embolism, indicating functional similarity between both types of conduits. Interconduit pit membrane thickness (Tm) was the only measured anatomical feature that showed a relationship to significant vulnerability to embolism. Our results suggest that the incidence of drought in rain forest ecosystems can have similar effects on species bearing water-conducting cells with different morphologies. Show less
Dória, L.C.; Meijs, C.; Podadera, D.S.; Del Arco, M.; Smets, E.; Delzon, S.; Lens, F.P. 2019
• Background and Aims Plant survival under extreme drought events has been associated with xylem vulnerability to embolism (the disruption of water transport due to air bubbles in conduits).... Show more• Background and Aims Plant survival under extreme drought events has been associated with xylem vulnerability to embolism (the disruption of water transport due to air bubbles in conduits). Despite the ecological and economic importance of herbaceous species, studies focusing on hydraulic failure in herbs remain scarce. Here, we assess the vulnerability to embolism and anatomical adaptations in stems of seven herbaceous Brassicaceae species occurring in different vegetation zones of the island of Tenerife, Canary Islands, and merged them with a similar hydraulic–anatomical data set for herbaceous Asteraceae from Tenerife.• Methods Measurements of vulnerability to xylem embolism using the in situ flow centrifuge technique along with light and transmission electron microscope observations were performed in stems of the herbaceous species. We also assessed the link between embolism resistance vs. mean annual precipitation and anatomical stem characters.• Key Results The herbaceous species show a 2-fold variation in stem P50 from –2.1 MPa to –4.9 MPa. Within Hirschfeldia incana and Sisymbrium orientale, there is also a significant stem P50 difference between populations growing in contrasting environments. Variation in stem P50 is mainly explained by mean annual precipitation as well as by the variation in the degree of woodiness (calculated as the proportion of lignified area per total stem area) and to a lesser extent by the thickness of intervessel pit membranes. Moreover, mean annual precipitation explains the total variance in embolism resistance and stem anatomical traits.• Conclusions The degree of woodiness and thickness of intervessel pit membranes are good predictors of embolism resistance in the herbaceous Brassicaceae and Asteraceae species studied. Differences in mean annual precipitation across the sampling sites affect embolism resistance and stem anatomical characters, both being important characters determining survival and distribution of the herbaceous eudicots. Show less
Li, S.; Lens, F.P.; Espino, S.; Karimi, Z.; Klepsch, M.; Schenk, H.J.; ... ; Jansen, S. 2016
Pit membranes in bordered pits between neighbouring vessels play a major role inthe entry of air-water menisci from an embolised vessel into a water-filled vessel(i.e., air-seeding). Here, we... Show morePit membranes in bordered pits between neighbouring vessels play a major role inthe entry of air-water menisci from an embolised vessel into a water-filled vessel(i.e., air-seeding). Here, we investigate intervessel pit membrane thickness (TPM)and embolism resistance (P50, i.e., the water potential corresponding to 50% lossof hydraulic conductivity) across a broad range of woody angiosperm species.Data on TPM and double intervessel wall thickness (TVW) were compiled based onelectron and light microscopy. Fresh material that was directly fixated for transmission electron microscopy (TEM) was investigated for 71 species, while non-freshsamples were frozen, stored in alcohol, or air dried prior to TEM preparation for anadditional 60 species. TPM and P50 were based on novel observations and literature.A strong correlation between TPM and P50 was found for measurements based onfreshly fixated material (r = 0.78, P <0.01, n = 37), and between TPM and TVW(r = 0.79, P < 0.01, n = 59), while a slightly weaker relationship occurred betweenTVW and P50 (r = 0.40, P <0.01, n = 34). However, non-fresh samples showed nocorrelation between TPM and P50, and between TPM and TVW. Intervessel pit membranes in non-fresh samples were c.28% thinner and more electron dense thanfresh samples. Our findings demonstrate that TPM measured on freshly fixatedmaterial provides one of the strongest wood anatomical correlates of drought-induced embolism resistance in angiosperms. Assuming that cellulose micro fibrilsshow an equal spatial density, TPM is suggested to affect the length and the shapeof intervessel pit membrane pores, but not the actual pore size. Moreover, theshrinking effect observed for TPM after dehydration and frost is associated withan increase in micro bril density and porosity, which may provide a functionalexplanation for embolism fatigue. Show less
