Abstract
The effects of drought stress on phospholipase D (PLD) gene expression and enzymatic activity were investigated in ‘Pineapple’ sweet orange. PLDs are tissue-specific, with overlapping functions, and in response to stress they may interact with ABA signaling. Tissue specificity for expression of PLDs and their regulation are unknown in citrus. To assess PLD response to water stress and gene expression/regulation in citrus, we subjected potted seedlings to increasing levels of soil drought. Evapotranspirational demand (ET) was estimated by measuring weight loss in pots, and water stress was further assessed by measuring ABA content. Three treatments were performed over a 3-week period: (a) Control treatment without drought stress (100% of daily ET); (b) mild water stress (50% ET); and (c) severe water stress (0% ET). ABA content increased during drought stress in both roots and leaves, being higher in leaves than in roots by the end of the experiment for any stress condition assayed. PLD enzymatic activity was monitored and expression of five PLD genes was studied. PLD activity increased linearly over time in response to increased soil drought and was around three times higher in roots than in leaves. PLD activation occurred initially in roots and then in leaves. PLD gene expression in response to stress soil drought differed between roots and leaves. These results show the potential of PLD as a suitable indicator of stress severity in citrus.
Highlights
Physiological responses of trees to the environment rely on factors such as leaf morphology and anatomy, along with xylem vessel area, size, and density, as they play a role in stomatal conductance, and subsequent biochemical changes that contribute to differences in functional capacities [1,2]
We investigated the effect of increasing water stress on phospholipase D (PLD) activation in the whole citrus plant, with the objective of identifying drought conditions in the soil necessary for induction of this enzymatic activity in the tree that could serve as an indicator of deleterious water stress
PLD interplays with abscisic acid (ABA) in the response of plants to water stress [17,18,19,20], the aim of this study was to investigate how drought, ABA accumulation, and PLD activation operate in citrus trees
Summary
Physiological responses of trees to the environment rely on factors such as leaf morphology and anatomy, along with xylem vessel area, size, and density, as they play a role in stomatal conductance, and subsequent biochemical changes that contribute to differences in functional capacities [1,2]. Among abiotic stresses affecting plant productivity, water stress is the most important environmental agent causing losses in crop yield and quality [3,4,5,6]. Water stress is a main cause of yield losses due to physiological alterations such as preharvest fruit drop and leaf abscission [7,8]. The responses of plants to drought vary depending on the severity of the stress and the stage of drought progression. In this regard, it has been proposed that monitoring soil moisture status in combination with measuring molecular, biochemical, and physiological responses in the plant may allow quantification of plant responses to drought severity [10]. There are abundant evidences of Agronomy 2020, 10, 45; doi:10.3390/agronomy10010045 www.mdpi.com/journal/agronomy
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