First year cuttings of virus-free hop plants were obtained from Hop Research Institute in Žatec and
after 6 weeks of cultivation in 10L containers in the glasshouse were used in experiments. Three
cultivars were used in experiments – traditional Saaz hops (Osvald’s clone 31 - OC31), cultivar
Agnus and hybrid cultivar Vital.
Leaf water potential (WPL) was estimated by dew point psychrometry (Wescor HR33, Wescor Inc. USA)
on cut leaf discs.
Soil water content was monitored using ThetaProbe (Delta-T Devices Ltd., UK).
Transpiration rate of whole intact plants was estimated gravimetrically.
Measurement of cavitation and sensitivity to cavitation: Degree of cavitation was measured in stem
segments. The method was based on measurement of stem conductivity (see below) for KCl solution
before and after removal of embolism from xylem (using the perfusion under high pressure -140 kPa).
Percent loss of hydraulic conductivity (PLC) due to embolism was calculated as relative increase of
initial conductivity after embolism removal by the high pressure flush /4/.
Specific conductivity of stem xylem: The method was based on measurement of flow rate of filtred
(0.2 um) 10 mM KCl solution through the stem segments (longer than 1 m) under stable pressure
gradient /4/. The flow rate was determined by directing the solution flow to a precise analytical
balance and data collected with data acquisition software in connected computer. Measurement of
stem water potential (WPS) was based on equilibration of WPL and WPS in leaves sealed in plastic
bag overnight and subsequent measurement of WPL /5/. pH microelectrode was used for sap pH
measurements, UPLC-MS/MS for ABA analysis. Relationships between net photosynthesis, transpiration
rate and leaf water potential was measured by Cirras 2 (PP systems, UK) gas exchange system.
Reduction of the total precipitation has a negative impact on the yield of hop /1/. Introduction of
drought tolerant cultivars is one possible solution for this problem. However, a lack of
information about physiological traits related to drought tolerance of hops and their variability
among cultivars complicates breeding and selection attempts. This work presents first information
about response of basic physiological processes of hop plants under decreased water availability.
It also compares differences in response to drought among hop cultivars /6, 7/.
Describe, how leaves of hop plants respond to decrease of soil water availability.
Examine, how hydraulic conductance of stem can be affected by decrease of stem water potential and
consequent cavitation.
Investigate, how the long-distance chemical signals contribute to the limitation of transpiration
rate under drought.
The relationship of the net photosynthetic rate and water potential of leaves of OC31 cultivar. The
relationship indicates (with respect to diurnal WPL changes) that in dry soil may be net carbon
assimilation reduced to 30-40% of the rate of fully irrigated plants.
The mean diurnal changes of leaf water potential (WPL) in well watered and drying OC31 plants
measured on hot and sunny day. Pattern shows that hop belongs to anisohydric plants – its WPL
lowers during the day /2/. Dry soil resulted not only in reduced WPL but also in its greater
variation. Observed response in dry soil may be related to either smaller restrictions in stomatal
regulation under drought or to insufficient water transport to leaves from roots via xylem.
The response of transpiration rate of intact plats of hop cultivars Agnus and Vital to changes of
soil water content. Transpiration was progressively reduced in drying soil in both examined
cultivars. Slower decrease of transpiration was observed in cultivar Agnus in comparison with
Vital. Agnus also showed significantly smaller maximum transpiration rates. These traits may
indicate better drought tolerance of Agnus. Each point represents one measurement of single plant.
/1/ Hlavinka P, Trnka M, Semeradova D, Dubrovsky M, Zalud Z, Mozny M. 2009. Effect of drought on
yield variability of key crops in Czech Republic. Agricultural and Forest Meteorology 149 :
431-442.
/2/ Schultz HR. 2003. Differences in hydraulic architecture account for near-Isohydric and
anisohydric aehaviour of two field-grown Vitis vinifera L. cultivars during drought. Plant Cell and
Environment 26: 1393-1405.
/3/Tibbetts TJ, Ewers FW. 2000. Root pressure and specific conductivity in temperate lianas: exotic
Celastrus orbiculatus (Celastraceae) Vs. native Vitis riparia (Vitaceae). American Journal of
Botany 87: 1272-1278.
/4/ Sperry JS, Tyree MT. 1988. Mechanism of water stress-induced xylem embolism. Plant Physiology
88: 581-587.
/5/ Ewers FW, Fisher JB, Chiu ST. 1989. Water transport in the liana Bauhinia fassoglensis
(Fabaceae). Plant Physiology 91: 1625-1631.
/6/ Gloser V., Baláž M, Jupa R, Korovetska H, Svoboda P. 2013. The response of Humulus lupulus to
drought: contribution of structural and functional plant traits. Acta Horticulturae 1010: 149-154.

/7/ Korovetska H, Novák O, Jůza O, Gloser V. 2014. Signalling mechanisms involved in the response
of two varieties of Humulus lupulus L. to soil drying: I. Changes in xylem sap pH and the
concentrations of abscisic acid and anions. Plant and Soil 380: 375–387.
Introduction
Aims
Methods
Whole plant response
Conclusions
References
Acknowledgments
We thank Olda Jůza and Martin Rozmoš for their excellent technical assistance. This work was
supported by the the Czech Science Foundation project no. 206/09/1967. Presentation of this work
was supported by project by project PASSEB.
The relationship of the relative loss of hydraulic conductivity of stem xylem on stem water
potential of hop. This embolism vulnerability curve shows better resistance to embolism than woody
stems of lianas Vitis riparia and Celastrus orbiculatus (PLC50 = 0.2 - 0.5 MPa, /3/). It also shows
that native embolism in plants in both well watered and moderately drying soil is below 20 % (group
of points marked with a circle). This finding suggests that transport in the stem xylem is not
limiting for water delivery to leaves.
Leaf water potential fluctuates during day from -0.5 to 1.5 MPa with greater amplitude in
water-limited plants. Drought lowers net photosynthesis to 30 to 40% of well watered plants.
Embolism present in intact plants even in dry soil is below 20%. The conductivity of stem xylem is
probably not the most limiting step for water delivery to leaves.
Transpiration of hop plants responds sensitively to changes in soil water content and there are
differences among cultivars in this response.
Long distance chemical signals from root contribute to stomatal regulation in hop plants.
What Limits Growth of Vines
Under Drought ?
Vít Gloser1, Milan Baláž1, Halyna Korovetská1, Petr Svoboda2
1Masaryk University, Institute of Experimental Biology, Kotlářská 2,
611 37 Brno, Czech Republic, VitGloser@sci.muni.cz
2Hop Research Institute, Kadaňská 2525, 438 46 Žatec, Czech Republic
hops_leaf_v B-gt Fig 3b
Changes of transpiration rate along with leaf water potential. Steep decline in the first part of
approximate trend curve (on the right side) indicates that significant reduction of transpiration
occurs before any changes in WPL. Each point represents measurement on one plant.
Hydraulic limitation
Chemical signals
Хylem sap pH increased in both cultivars at the early stage of soil drying before any changes in
leaf water potential occurred. Elevated pH of leaf apoplast can affect redistribution of ABA in
leaf mesophyll, which results in greater availability ABA to receptors of stomatal cells.
Concentration of ABA in sap increased exponentially under declining SWC. This indicates that ABA
transport is important signal in the later stage of soil drying.
Measured transpiration rate of hop plants was similar to estimated evaporation rate on hot sunny
day. Practically measured TR was only up tp 30% of the potential TR calculated from stem hydraulic
conductance and difference in water potentials of leaf and soil.