Abstract
Water is considered perhaps the most limiting factor for plant growth and productivity (Boyer, 1982), and climate change predicts more frequent, more severe and longer drought periods for a significant portion of the world in coming years. Unfortunately, drought resistance is particularly difficult to measure due in part to the complexity of the underlying biology that contributes to a plant’s ability to cope with water limitations. For example, water deficit is frequently examined by detaching leaves or withholding water for a set period of time prior to tissue collection. Such approaches may elucidate the early stages of drought response but are generally not physiologically relevant for maintenance of drought resistance over a longer period. A more realistic approach is to impose a gradual water limitation with a sustained soil moisture level, particularly in the case of woody perennials. We describe here a protocol that imposes a long-term water deficit under controlled laboratory conditions that allow a molecular biology approach to understanding how woody plants survive severe water limitations. Representative data can be found in Artlip et al. (1997) and Bassett et al. (2014).
Keywords: Malus x domestica, Tissue culture, Water limitation, Climate change, Pressure bomb
Materials and Reagents
Equipment
Procedure
Representative data
Figure 1. Young apple trees of cultivar Royal Gala from drought experiment. T1C: control trees two weeks after the beginning of the experiment. These trees were watered to saturation (90-95% pot weight). Arrow shows new leaf unrolling at shoot apex. T1E: experimental trees two weeks after being held at 40% saturation. Filled arrow marks dying shoot apex; open arrow shows leaf curling which is a common indicator of dehydration. Photographs were taken from Bassett et al. (2011) with permission from the American Society for Horticultural Science. Figure 2. Typical water deficit experiment in the growth chambers Apple trees ~ 1 m tall were selected, tagged and placed in the Conviron growth chamber. The figure shows trees with and without foil placed on the pots. Red tags represent water deficit treatment; blue tags represent well-watered controls. A. Water deficit treatment and controls without foil; B. Water deficit treatment with foil covering pot surfact. Figure 3. Leaf number of ‘Royal Gala’ trees subjected to a severe drought. The number of leaves along three regions of the stem were counted as follows: young leaves (1-2 cm long) at the top of the plant, leaves (~4-6 cm long) along the middle of the plant, and leaves (~7-8 cm long) along the lower portion of the plant. Pots of water-restricted plants were maintained with (WUE + foil) or without (WUE - foil) foil covers for the duration of the experiment. Controls were well watered with no foil on the pots. The number of leaves was counted every other day for two weeks. The greatest difference in leaf loss due to water deficit is seen in the youngest leaves just beginning expansion, whereas oldest leaves having expanded before the water deficit was imposed show the least difference.
Notes
Recipes
Acknowledgments
This work was funded by USDA through the Agricultural Research Service as part of the in-house appropriated funding. We would like to acknowledge the contribution and excellent technical assistance of Sharon Jones.
References
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